Continued from No. 82.
The features that determine cost in a structure are: first, the cost of production, or first cost; second, the cost of maintenance, or care; third, the length of life.
D.—COMPARISON FOR FIRST COST.
The cost of production, or first cost, is made up of cost of material as supplied by the dealer or manufacturer, cost of labor expended in construction, deterioration of plant entailed, and interest on capital invested. The cost of labor is here taken to include draughting, superintendence, supply of power, etc.
1. Cost of Material.
a. Rolled Material.—The cost of ordinary mild steel used in hull construction may be taken at 2 cents per pound for both plates and shapes.
The cost of aluminum has not reached a steady level, continuing naturally to fall with the increase and improvement in methods of production. Roughly speaking, this increase in production has doubled each year for several years past, and though, for other causes, the fall in price has not been so rapid, it has been pronounced and must be expected to continue for some time to come.
It is difficult, therefore, to assign to aluminum a definite value, and any value assigned must be considered as only momentary. For the purpose of comparison, however, the cost of rolled aluminum at the present time may be taken at 40 cents per pound for plates and 6o cents per pound for shapes, giving, compared with steel, the ratios per unit weight of 20 and 30 respectively.
(1) Plates.—As seen above, the ratio of weights for steel and aluminum in tension is .5 for equal ultimate strength, and .35 for equal elastic strengths. For plates, therefore, the ratios of cost in the two cases are 10 and 7 respectively.
The ratio of weights of plates for equal bending moments is .44 when working to the ultimate limit and .36 when working to the elastic limit. The ratios of costs, therefore, are 8.8 and 7.2 respectively.
The ratio of weight for equal stiffness is .648; the ratio of costs, therefore, is 9.6.
(2) Shapes of proportional dimensions.
The ratio of weights for equal bending moments when working to the ultimate limit is .55 for I beams and .58 for angles. The ratios of costs, therefore, are 16 and 17 respectively.
The similar ratios when working to the elastic limit are for weight .37 for I beams and .4 for angles, and for cost ii for I beams and 12 for angles.
The ratio of weights for equal stiffness is .4 for I beams and .62 for angles. The ratios of costs therefore are 12 and 18 respectively.
b. Cast Material.—It will appear below, if not already evident, that aluminum is unfitted for heavy ship castings, such as stems, sternposts, shaft struts, etc., by nature of its small resistance to unusual violent shocks. The comparison, therefore, need extend only to small castings for fittings.
The cost of cast steel for hull fittings may be taken generally at 10 cents per pound. The cost of cast aluminum for the same fittings may be taken at 6o cents per pound. The ratio of costs, therefore, per unit weight is 6.
In the range of cast hull fittings, the castings and parts of castings serve the function of covering like plates, of stiffness like shapes, and attachments like simple bars. Some castings and some parts of castings are designed with special regard to ultimate resistance, and others are designed with special regard to elastic resistance. The resistance in some cases is simple, in others compound. Taking a general mean for equality of resistance, the ratio of weight is .48. The ratio of costs therefore is 2.9.
Many cast hull fittings are made sometimes of cast steel, sometimes of cast brass; many are made exclusively of cast brass. It is therefore interesting to note that the comparison of aluminum with brass in these cases would give a ratio of weight of about .3 and of cost about .9. Recalling, too, that the two metals are more or less alike in relative softness and ease of working, it may be said roughly that the aluminum fittings giving the same strength as brass fittings have the same cost, with only one-third the weight.
It should be borne in mind, however, that this comparison, as also the comparisons with steel, assumes a degree of perfection in casting aluminum scarcely warranted at the present moment. It is given, however, in view of the rapid progress being constantly made in the new art of casting aluminum.
2. Cost of Labor.
a. For Rolled Material. (I) Hull work proper.—For steel the cost of labor in large hull work, plates and shapes may be taken at 4 cents per pound. For aluminum, on account of its newness and limited application, definite figures or results and estimates of the cost of labor in construction are lacking, and, despite of efforts, have not been attainable. The comparisons, therefore, must be limited to a general appreciation only.
The term labor, in estimates of hull construction, includes all operations of transportation and handling in yard and in shops, all operations of preparation of the material, laying off, punching, shearing, planing, bending, flanging, trueing, all operations of adjusting and securing in place, bolting, drilling, riveting.
In operations of transportation, handling and adjusting, the great lightness of aluminum work, less than half the weight of corresponding steel work, permits of marked economy in the number of men and length of time required.
In operations of tool work, planing, shearing, chipping, drilling, etc., the greater softness of aluminum insures a similar marked economy. The same feature of softness gives a marked economy in riveting, all work being riveted cold, doing away with the portable forges and reducing the number of the riveting gangs.
On the other hand, the greater elastic elongation and the immensely smaller ultimate elongation of aluminum cause the operation of shaping, rolling, bending, flanging plates, bending and trueing shapes to be more difficult and more delicate, requiring longer time and greater skill. This drawback, evidently, is much more pronounced for shapes than for plates, the operation of trueing under the beam set involving, indeed, danger of destroying the integrity of the shapes.
The relative importance or amount of labor in these various operations depends evidently on the nature of the piece of work. Taking hull work throughout, and considering all the operations involved, the advantage sets emphatically to the side of aluminum in the case of plates, but is probably against aluminum in the case of shapes.
For the sake of continuing the numerical comparison, the advantage of aluminum over steel for plates is estimated at 25 per cent., while the advantage of steel over aluminum for shapes will be taken at the same figure. These figures, however, must be regarded as results of inductive judgment only.
Thus for aluminum the cost of labor in large hull work is taken for plates at three-fourths and for shapes at five-fourths the cost of steel for the same work.
Taking the weight ratios roughly at one-half, the cost of labor becomes for plate work 6 cents per pound and for shapes 10 cents per pound.
(2) Hull fittings.—For rolled steel the cost of labor in hull fittings may be taken broadly at 20 cents per pound.
The observations on the comparison for hull work hold in general for hull fittings. The operations of transportation and handling, however, become of less consequence, reducing the advantage of aluminum. On the other hand, the operations of shaping and trueing become likewise of less consequence, while the operations of small tool work, chipping, drilling, etc., become more pronounced in favor of aluminum. For the present purpose, therefore, the price ratio may be taken at three-quarters for shapes as well as plates; with the same weight ratio, the cost of labor for aluminum hull fittings becomes 30 cents per pound.
b. For Cast Material.—Confining the comparison, for the same reason as given above, to small castings for hull fittings, the cost of labor for steel castings may be taken broadly at 12 cents per pound. The cost of labor for aluminum castings for the same fittings may be taken at 16 cents per pound, giving a cost ratio of about two-thirds, using the same weight ratio of one-half.
3. Other Costs.
All other costs, including deterioration of plant, interest on capital invested, shop expense, supply of power, draughting, superintendence, etc., may be grouped together. For steel work the cost of the whole group may be taken at 25 per cent. of the cost of labor, in which the allowance for deterioration of plant is taken at about 10 per cent, per year and the interest on capital invested at about 10 per cent, per year.
For aluminum, it is evident that the lightness and softness will materially reduce the cost of deterioration of plant and shop expense, requiring less power, with less strain on machines, and less usure and dressing of tools. The group cost may be taken at four-fifths the cost for steel work.
These rates give the following results:
For Rolled Material.
Cost of Labor. Group Cost.
For steel hull work, plates and shapes 4c. per lb. 1c. per lb.
For aluminum hull work, plates 6c. " " 1.6c. " "
For aluminum hull work, shapes 10c. " " 2c. " "
For steel hull fittings, plates and shapes 20C. " " 5c. " "
For aluminum hull fittings, plates and shapes 30c. " " 8c. " "
For Cast Material.
For steel hull fittings 12c. per lb. 3c. per lb.
For aluminum hull fittings 16c. per lb. 4.8c. per lb.
4. Summation for First Cost.
The results thus found for the elements making up first cost are assembled in a table.
The striking feature of this table is the reduced ratio of total costs, due to the fact that cost of material in which steel has so heavy an advantage is but one item, while cost of labor and other costs are items of much greater consequence, in which the advantage is slightly on the side of aluminum.
These results are specially pointed out in connection with the applications below, but attention may be called at once to the uniformly small weight ratio, a saving of over one-half in weight, and the comparatively small cost ratio for hull fittings and small castings, and to the marked difference of cost ratio between plates and shapes for hull work, the comparison for first cost thus pointing to the adaptability of aluminum in the following relative order: first, to plate work in hull fittings, with increase over cost of steel work of only 24 per cent.; next, to small castings in hull fittings, with increase of 48 per cent.; next, to shapes in hull fittings, with increase of 74 per cent.; next, to plates in hull work, with 2.8 times the cost of steel; next, to shapes in hull work with 5 times the cost of steel.
E.—COMPARISON FOR COST OF MAINTENANCE AND CARE AND LENGTH OF LIFE.
Obstructions have stood in the way of every advance in human industry. Scarcely an advantage has been won without antagonism and offsetting disadvantage. When, therefore, not many years since, the industrial world, wrestling with steel and iron, saw aluminum appear above the horizon as a commercial article, Promising the great desideratum of strength without the penalty of weight and excessive hardness, it felt a thrill, and the more impetuous, foreseeing correctly the inevitable reduction of cost, thought that man had come into a new province without the strife of conquest, proclaiming in effect an abdication by terrestrial nature of her inexorable law of struggle.
The marine engineer and architect felt the elation above all others, for weight in construction material is the Goliath of their enemies. Only prudence and conservatism interposed to prevent precipitate application of the new metal. The conservative asked if aluminum was in truth a fully constituted David. The first reconnaissance showed an obstacle in the road, of huge proportions, not to be removed by the hand of a boy or the aim of a sling. Salt water and salt air were found to attack and disintegrate the metal.
Three notable cases of aluminum construction followed each other in rapid succession, the Vendenesse, built in France in 1892 and 1893, the Foudre, built in England in 1893 and 1894, and the Defender, built in the United States in 1894 and 1895. All three of these craft more than realized the expectations of performance, but all of them have demonstrated the weak point of aluminum. All have been exposed in varying conditions to the corroding action of salt air and salt water, and have contributed to the knowledge of this unfortunate phenomenon.
The Vendenesse, sloop-rigged sailing yacht, built at St. Denis, has her shell plating, decks and bulkheads of aluminum, 6 per cent, copper alloy, while her frames, keel and stringers are of steel, the weight of hull by this disposition being but 18 per cent, of the displacement.
Shortly after launching in December, 1893, she was dropped down to Havre, and lay in the salt water basin for about four months without attention. Her water line showing signs of corrosion, she was docked and her bottom was found bare with the paint off about 2oo square metres of surface, part of the Paint at least having been scraped off by obstacles while coming down the Seine. Examination showed corrosion wherever the metal was exposed, pitting being particularly pronounced around the edges of bare spots.
An investigation as to the causes of such pronounced results in so short a time showed, however, that part of the corrosion was undoubtedly due to galvanic action that set in from the proximity of a schooner with copper bottom, and, moreover, the basin received sewer discharges and had imperfect renewal of water.
The subsequent history of the yacht showed conclusively, however, that the metal would be attacked whenever exposed. It showed also practically continuous slow galvanic action, even between plates, both of which were of aluminum. The joints swelled and strained the rivets. One plate only would be corroded, showing lack of homogeneity and the existence of a voltaic circuit.
The deck plating was irregularly attacked; plates here and there had to be removed. The linoleum covering gave partial protection, but not immunity.
The excellent nautical qualities and the mechanical behavior of the metal made the yacht a decided success, but it was found that a specially prepared paint had to be used and that special care and almost constant attention were still necessary for even imperfect preservation.
The Foudre, second-class torpedo-boat, 6o feet long, 9 feet 3 inches beam, 4 foot draft, built by Yarrow for the French Government, and intended for the torpedo cruiser Foudre, is built practically throughout hull and hull fittings of aluminum, worked cold, realizing a saving of about 25/2 tons, equal to about half the weight of hull, and about 25 per cent. the weight of total boat.
The stem and sternpost are of galvanized steel; the rivets, where exposed to bilge water, were of iron, elsewhere they were of aluminum; the inner tube of smoke stack and deck plating around smoke stack exposed to heat and a small part of the deck where special strength are required, are of steel. The propeller is of aluminum bronze.
The bottom and inside throughout were painted with red lead and the deck was covered with rubber canvas glued on. After successful trials in the fall of 1895, on which the speed realized was 1 ¾ knots in excess of contract speed, the boat was taken to Cherbourg and left at moorings all winter, apparently without being visited.
When examined the following spring, corrosion was found to be practically general. The outside of hull was pitted 'wherever exposed, and the inside was corroded practically throughout. Conning tower and hull fittings, exposed only to the salt air, were likewise uniformly corroded wherever uncovered, though the rubber canvas was effective in preserving the deck.
The result showed that red lead favored and produced corrosion. Moreover, when once begun, corrosion continues unless the metal is thoroughly scraped and cleaned before painting again. To clean the parts thoroughly would have required taking the boat to pieces, so general was the corrosion. The interesting little craft, so unfortunately treated, was practically given over to inevitable disintegration. The five sister boats, first ordered of aluminum, were changed to steel, and the torpedo cruiser was converted to an ordinary first-class cruiser, though it does not necessarily follow that this conversion was due alone to the failure of the aluminum boat.
Referring to the method of construction of Defender, given above, it will be recalled that the top side plating, deck beams, deck strapping, and upper fittings are of aluminum, 4 per cent. nickel alloy, the bottom plating is of bronze, and the stem, frames, floor plates and stiffening angles, bilge stringers, inverted angle bulbs under deck beams, the two deck beams enclosing mast, tie plates around mast, stepping socket, bed plate fittings and supports and chain plates are of steel, while the rivets are of bronze, making thus an intimate association of the three metals.
After completion afloat at Bristol in July, 1895, Defender was taken to New Rochelle. Examined there, the aluminum topsides were found to be in bad condition, with paint off in patches, particularly along water line, showing signs of corrosion along the seam of juncture of bronze and aluminum.
She was docked, washed, sand-papered and painted, and was similarly treated three times more before leaving for the races in September, on each of which occasions there were evidences of corrosion wherever the aluminum and bronze were in contact, and, to a less degree, wherever aluminum was water-washed.
Returning to New Rochelle after the races she was next examined in January, 1896, and was found to be corroded practically all over, corrosion being found underneath the paint, even where it appeared solid. The inside, too, was slightly corroded all over, with severe corrosion in closets.
She was scraped throughout, washed with benzine and given four coats of paint on the outside and two coats on the inside. It may be recalled, in referring to painting, that the bronze surface of bottom is left bare.
The next examination, five months later, in June, showed corrosion at the water line, along the seam of juncture of aluminum and bronze and around rivet heads, a few rivet heads having fallen off, also corrosion around the chain plates, apparently due to leakage from deck. Corroded parts were scraped and touched up and deck leaks stopped.
The above examinations were made by the care-taker of the yacht, from whose log record the information is taken.
Two months later, in August, as previously referred to, an inspection was made by the writer, and the results, as above given, were fully confirmed.
It was found, in addition, that the cast fittings on deck, such as deck light frames, exposed on the whole to spray and salt air only, were in the last stages of consumption, and in many cases the spongy, honeycombed metal could be broken and crumbled with the hand. On the outside along the seam of juncture of aluminum and bronze, a close inspection showed a series of small mounds for practically the whole length. Upon puncture these mounds were found to be raised by the gray powder of corroded aluminum. On the inside this gray powder of corrosion covered the ledge formed by the top of the inside plating, the system being, as seen above, the raised and sunken system, and by jarring the sides more powder would sift down, showing a general process of corrosion.
Additional rivet heads were found fallen off and an examination of the fracture showed the force of rupture to be mechanical, there being nothing more than usual verdigris on the surface. The only way to account for this breaking off of rivet heads is the supposition of strains set up by the swelling due to the corrosion of the plates connected, combined with the slight elongation capable of being sustained by bronze. This swelling, as seen above, was found on the Vendenesse, and, moreover, appears inevitable when it is recalled that the process of corrosion forms a less compact substance, more bulky, than the metal.
Down from around a number of rivet heads and from the edges of the chain plates extended the yellow-brown streaks of iron corrosion. The steel frames and other steel work are being corroded by the bronze rivets and plates. The vessel presents undoubtedly a series, a network, of voltaic circuits, and it would be interesting to have a galvanometric survey.
Thus in Defender, too, we see a full realization of all the mechanical advantages sought in aluminum, and full satisfaction of behavior under stress of service; but we see too upon her the loom of a short life. In her system are working the fatal germs of the phthisis of corrosion.
Besides the three notable cases of the Vendenesse, Foudre and Defender, there have been others in which aluminum has been used to a greater or less extent, furnishing additional experience on preservation and length of life.
The Forban, first-class torpedo-boat, built for the French Government in 1893 and 1894, by Normand, at Havre, had her low pressure pistons and piston valves and her conning tower, galley, framing for turntables, torpedo tubes and other fittings of aluminum, realizing a saving in weight of about a ton. The results were unsatisfactory for all of these parts and fittings; the Piston and valves did not meet the requirements for strength, though it should be recalled, as stated above, that even a comparatively low temperature must be expected to effect the strength of aluminum; the parts and fittings on deck within 12 months gave bad results of corrosion, flaking off in parts, notwithstanding care in painting. The result was that Normand abandoned the use of the metal.
On the torpedo-boats built at the New York Navy Yard and intended for the Maine, a number of cast fittings, principally on deck, such as stanchions, sockets, deck light frames, etc., were first made of aluminum. The metal exhibited brittleness and showed signs of corrosion, and in consequence was abandoned, though it should be stated that measures to prevent corrosion were not attempted.
Some of these fittings left exposed longer to sea air were entirely disintegrated, becoming spongy and flaky, and crumbling to gray powder as found in deck fittings of Defender described above.
Other craft have been built wholly or in part of aluminum, but have not furnished data, yet attainable, on the corrosive behavior of the metal.
A twenty-three foot electric launch, of 8-knot speed, of about three thousand one hundred pounds displacement, built at Toulon for the service of the Navy Yard, is practically aluminum throughout—plating, stem and sternpost, frames, rivets, etc., realizing the remarkably small hull weight of 346 pounds, or one-ninth of the displacement, the plates being but .078" thick. The aluminum is 6 per cent, copper alloy. This little craft has been in use some time, and has probably evinced interesting features as to corrosion, complicated in all probability by the presence of the storage battery and motor for propelling, but information is not to hand as to results.
Another interesting craft, which in due time will probably give valuable information on the subject of the preservation of aluminum, has recently been built at Nyack on Hudson, a fortyfoot launch, designed to develop 200 horse-power and exhibit a very high speed; designer, Chas. D. Mosher; owner, P. Magown, Esq.
This launch has her frames, bilge stringers, keelson, and deck beams of aluminum, the planking being mahogany and keel oak. Adequate measures have been taken in advance with a view to prevent or reduce corrosion. The aluminum is not in contact with copper or other corroding metals; it is nickel alloy, which alloy, as will be seen below, offers better resistance to corrosion than copper alloy, and is coated with 4 coats of special enamel.
The results of behavior under conditions of service will doubtless be valuable.
It may be mentioned here that a number of other craft have been built of aluminum for service in Africa and Madagascar, about twenty-five in all, many of which are built in sections for transportation on the backs of pack animals and couriers. Some of these craft have been in service for a number of years, the Etienne and Davoust being among the pioneers.
No returns have come as to behavior. They doubtless serve their purpose with efficiency, but, navigating fresh water, cannot furnish information of value on the question of corrosion, for, as seen below, aluminum has been found to resist effectually the action of fresh water. It is only salt water and salt air that assail it so disastrously.
The weight of experience, as thus seen above, sets against aluminum. While the object sought in saving of weight was fully realized in each instance, and the mechanical behavior has been satisfactory in every respect, the metal has proved a uniform failure on account of galloping corrosion. When examined more closely, however, the results appear far from conclusive. In the case of the Vendenesse and Foudre the material was a copper alloy. Copper is far removed from aluminum in the electro-chemical scale, and should be expected to make an alloy specially liable to galvanic action; indeed the combination in the alloy itself practically contains the elements of a battery. As a matter of fact, the copper alloy, which offers but very slight, if any, advantage for resistance over other alloys, such as nickel, is the most corrosive of all, the zinc alloy perhaps excepted. Moreover, the paint put on the Foudre to protect it was itself an active agent of corrosion, and both vessels were exposed to conditions that would be severe for a steel hull. It is reported that the special paint used on the Vendenesse in three coats, the first coat having special properties against corrosion, the second against permeability of water, the third against fouling, has given results more or less satisfactory.
In the case of the Defender, while the nickel alloy is used solely perhaps for its physical properties, it is in direct and most intimate contact with bronze, no effort at insulation of any kind Whatsoever being made, not even simple precautions that would have been insisted on in an ordinary case of steel and bronze construction. The yacht was built for one sole purpose—to win one series of races—and features not bearing upon that purpose were altogether ignored.
It is evident thus, that the case against aluminum is not complete, and the abandonment by the different governments of its further use in marine construction as a result of the excessive corrosion in the cases tried—this action, while conservative, and perhaps for the moment simply cautious—is by no means final.
The case is one that eminently calls for thorough scientific investigation and experiment, covering the range of alloys and the range of paints or preparations, those now existing and new ones that suggest themselves.
Partial and isolated experiments have already been made.
In connection with the decision to use aluminum for certain fittings for the torpedo-boats intended for the Maine, referred to above, and in connection with a proposition to introduce the general use of aluminum for hull fittings in naval vessels, tests were made by the Naval Constructor at the Norfolk Navy Yard to determine the resistance to corrosion and fouling.
Two plates, 12" X 18" X 1/16", furnished by the Pittsburgh Reduction Co., one of pure aluminum, the other of nickel alloy, were immersed with metal bare for three months in tideway water. When taken out in October, 1894, the nickel alloy plate was reported to be thickly covered with small barnacles and very considerably wasted away and corroded, and the pure aluminum plate was reported as "more thickly covered with larger barnacles and slightly pitted throughout its surface."
In January following another test was made.
Two plates were used, 14" x 16" x 1/8", furnished by the Pittsburgh Reduction Co., one of pure aluminum, the other of 6 per cent. copper alloy. Both plates were immersed with metal bare for 136 days, being taken out for examination after 40 days, and remaining out for 8 days, being cleaned before reimmersion. When finally taken out the pure aluminum plate was reported as showing no signs of corrosion beyond a few small pits, and was only "very slightly fouled" with a "few small barnacles." The copper alloy plate, on the contrary, was reported as "covered with a quantity of small barnacles," " badly fouled and pitted over its entire surface."
These tests, in their limited extent, would indicate that the bare metal of both the copper and nickel alloy is subject to corrosion and fouling in sea water, and that the pure aluminum, commercially pure, was subject but very slightly to corrosion. On the fouling of pure aluminum the results are more or less contradictory, and would indicate a difference of material in the two cases, though indicating that the commercially pure metal is subject to fouling. The exact degree or rapidity of corrosion was not determined, and it would be difficult to compare same with the results for ,steel under similar conditions.
The above limited experiments confined to bare metal are, it appears, the only ones that have been made in this country under Government directions.
Private tests have been made, however, extending to the behavior of the metal when coated with preventatives of corrosion.
The most extensive of these tests were undertaken by Edward Smith & Co., of New York City, and conducted under the direction of Professor A. H. Sabin, the aluminum plates being furnished by the Pittsburgh Reduction Co.
The scope of the tests covered five different kinds or series of Plates and six different coatings for each kind, making thirty Plates in all.
The plates, carried horizontally, supported by the four corners in a rack, with about 2" between plates, were immersed in the waters of the New York Navy Yard for six months.
The tests were described in a paper read by Professor Sabin before the American Society of Civil Engineers, contained in the Proceedings of the So6iety, vol. xxii, No. 7, September, 1896.
The composition of the plates, the nature of the coatings, and the results were as follows, as given in the paper above referred to.
COMPOSITION OF PLATES.
"Series I.—Ninety-nine and one-half per cent. pure aluminum.
Series II.—Ninety-eight per cent, aluminum and 2 per cent. copper.
Series III.—Ninety-eight per cent. aluminum (the quality known as commercially pure aluminum).
Series IV.—Ninety-three per cent. aluminum and 7 per cent. Copper.
Series V.—Seventy-five per cent. aluminum, 20 per cent. zinc, 3 per cent, copper, 1 per cent. iron.
The varnish in which the ultramariffe blue, flamingo red, white zinc and chromium oxide were ground was composed of 100 pounds Kauri resin to 20 gallons linseed oil, thinned with turpentine. The chromium oxide was the anhydrous oxide made by the ignition method, and was of commercial quality, not chemically pure. The baked coatings were baked about four hours at 2150 to 2400 F., except that the 'Sabin Process' pipe coating enamel was baked two hours at 4000 F."
The condition of each plate after being taken out is given by Mr. Sabin as follows:
SERIES I.
101.—Perfect.
102.—Baked side, perfect. Unbaked side, three blisters 14 inch diameter. No general corrosion or roughening. The surface of the paint had lost its gloss. The coating was good on the edges of the plates.
103.—Ultramarine blue. Showed roughening of coating, numerous pin-head blisters, no corrosion to speak of. Flamingo red. General condition good, except near edges of plate, which showed blisters over a surface about half an inch wide and one-fifth the marginal distance; very little corrosion.
104.—Baked side. About 2 square inches in one place half covered with small blisters. No corrosion. Unbaked side. First rate condition.
105.—Baked side, one blister x 1/2 inch; otherwise first rate.
No corrosion. Unbaked side all right.
106.—Both sides perfect.
SERIES II.
107.—Perfect.
108.—Baked side, one blister inch diameter. Unbaked side perfect.
109—Blue and red about the same as 103, except that about twice as much surface was blistered. General condition good.
110.—Baked side badly blistered in spots along the edges, amounting to about 6 per cent. of the total surface of the plate. Some corrosion under these. Unbaked side all right, except that about 1 per cent. of the surface showed pin-head blisters along a strip about 1/2 inch wide on one edge of the plate.
111.—Baked side showed four central 3/4-inch blisters, numerous marginal ones about i72 per cent. of plate. Very little corrosion. Unbaked side in first rate condition.
112.—Baked side, two central blisters 2 square inches, and nearly all the margin 72 inch wide. Considerable corrosion. Otherwise perfect protection and higher lustre. Unbaked side, two central blisters 72 square inch and 1 square inch. Slight marginal corrosion. Coating evidently thin on edges.
SERIES III.
113.—At one corner evidently a break in the coating let in water and caused a blister of about 2 square inches. Coating rather overbaked and brittle; elsewhere perfect.
114.—Baked side perfect. Unbaked side tough and adherent, except one small spot near the middle of the plate, which looked as if coating had been broken, and where corrosion had begun.
115.—Blue and red about alike. No decided blisters, but coating itself showed some signs of decomposition, especially the blue, which had a rough surface.
116—Both sides in good condition, but showed some signs of Incipient blistering about the edges.
117.—All right on both sides.
118.—Both sides quite perfect.
SERIES IV.
119.—At several places about the corners of the plate single blisters, some of which were as large as 3 square inches, had formed. These appeared to be due to the fact that the coating was overbaked and had been cracked at the corners by the sup- Porting framework, and galvanic action had ensued on the penetration of the sea water. This was facilitated by the 7 per cent. of Copper in the alloy. The remainder of the plate was perfect.
120.—Baked side showed three blisters of about i square inch each and some corrosion under these; otherwise all right. Unbaked side perfect.
121.--Blue and red about alike; about 30 per cent, blistered and corroded.
122.—Pin-head blisters along the edges; general condition all right.
123.—Baked side all right. Unbaked side, seven or eight small blisters, but no corrosion. General condition good.
124.—Both sides badly blistered and corroded along the edge, about To per cent. of the surface. Where not blistered, all right.
SERIES V.
125.—Coating brittle and certainly overbaked. Badly blistered along the edges. In all cases of blisters under pipe coating enamel the blisters were continuous and started from the edge. The middle of the plate was all right.
126.—Baked side badly blistered along the edge-6 per cent. or 8 per cent. affected. Unbaked side slightly blistered, chiefly along one edge; condition otherwise good. No corrosion.
127.—Blue. Considerably blistered along the edges, in pinhead blisters mainly. Little corrosion.
Red. About the same, but some large marginal blisters. The red had a smooth surface, but the blue was rough.
128.—Baked side, nine or ten blisters of some size (1 1/2 inches diameter), and considerable corrosion. Remainder of surface good. Unbaked side, about i per cent, of the surface, near the edges, with small blisters showing some corrosion. The rest of the surface all right.
129.—Baked side. A large number of groups (about 1 inch diameter) of small blisters. No corrosion. Unbaked side, about the same, but not so bad.
130.—About like 124.
The pigment mentioned as flamingo red is supposed to be a mixture containing some coloring matter derived from coal tar, and is reasonably permanent in the air. In these tests it became dark and mottled.
The baked surface of those plates which had one side baked were in all cases harder and more glossy than the other sides after the test was made. It should be observed, however, that while these coatings are all at present hard and firm, when they were first taken from the water they were much softer and could be more easily scratched or scraped off, with the exception of the pipe-coating enamel, which was exactly as it was when it was put into the water. Even the lustre was not affected, and the smooth plates coated with it are like a mirror.
On all the plates, except those coated with pipe-coating enamel which was applied by dipping, the coating is much thinner for about an inch along the edges of the plates than it is on the central portions. This fact has been called to the attention of the workmen who painted the plates, and is said to result from the method employed in applying the paint with a brush. In future experiments care will be taken to avoid this. Probably four-fifths of the corrosion occurred along this marginal strip."
The features of these tests, to be noted for the present purpose, are contained in the writer's remarks in the discussion of Professor Sabin's paper, part of which may be given as they were made, as follows:
"Alloys.—The prominent result of the experiments is that which shows that the corrosion increases as the amount of alloy increases, and that copper, as the alloy, particularly accentuates the corrosion. This result is striking in the comparison of the excellent results of Series III, where the alloy was simply 2 per cent, of the commercial impurities, with the unfavorable results of Series II, where the same amount of alloy, 2 per cent., was Copper. The interest in this feature is special, for it requires an alloy to develop the best conditions for strength, while among the alloys suited to this purpose, copper, though prominent, is by no means exclusive."
"Coatings.—The experiments, it is noticed, are restricted to varnish and enamel preparations. The favorable results indicate a field for these preparations for the preservation of fittings, if not for hulls.
Interest would attach to comparative tests of these preparations and those used on ships' bottoms, also with special preparations thus far made, and that may be prepared especially for aluminum. A feature that suggests itself from these experiments is that the insulating qualities, as well as the porosity or Permeability, may enter to affect results, and there would be interest in determining them in experiments to be made for comparative results. The generally unfavorable results with the baking process would indicate that the process increases the Permeability, while the increase of adhesion counts for but little when galvanic action starts beneath. Interest also would attach to determining whether the paints themselves, or any of their components, enter into the phenomena."
"Conditions.—The close proximity of plates of different alloys which varied widely in their galvanic action, affected, in all probability, the results in the individual cases. As far as practicable, while still insuring the same conditions, plates of different alloys should be separated far enough not to affect each other. Even those of the same alloy, having the different coatings, should be arranged so as to affect each other as little as possible.
An analysis should be made as near as can be of the mean sample water of immersion, to determine the special agents, if any, that are present.
If practicable, sets of similar plates and coatings should be tested in different waters and analyses of the water made in each case.
Both coated and uncoated plates of the same and different alloys should be immersed in vessels with sea water of sample kinds, and analyses, qualitative and quantitative, made as follows:
Of the materials of the plates before and after immersion; of the water before and after immersion; of the protecting coatings before and after immersion. These tests should be made progressively, analyses being made at regular intervals.
In addition, the tests should extend to determining the insulating properties of the coatings, and their permeability or porosity, in different thicknesses.
The object of the experiments outlined is apparent. They contemplate, while determining comparative qualities of different alloys and different preparations, to determine the phenomena that take place, and to find each element that enters and the role and relative degree of importance of each."
It is to be regretted that these valuable tests, already extended so largely, covering so large a range of alloys and range of varnishes and enamels, were not still further extended to cover the compositions now used on ships' bottoms, Rahtjen's, McInnis, red lead, etc., for it seems that adequate tests for these compositions have not yet been made.
The care-taker of Defender, Mr. T. S. Mitchell, painter, of New Rochelle, made experiments, as he described orally, in search of a preparation, and found the usual paints all gave bad results. He finally determined on a special paint of his own preparation, which was used exclusively. This is a white paint, apparently a white zinc paint, that tarnishes and streaks badly under weather, even under the drippings of condensation. Remark may be made of an experiment of Mr. Mitchell's which apparently reproduced the conditions found where the aluminum of Defender laps the bronze. A copper plate was placed on the back of an aluminum plate and put overboard. The result, of course, was a precipitate and destructive attack of the aluminum.
References may be made to a prior experiment with pure aluminum made in this country on the bottom of a wooden sailing vessel plying to the West Indies, where the test was comparative with copper.
The aluminum plate gave .005 in. corrosion where the copper Plate gave .007 in. On the other hand the aluminum plate was foul with marine growth, while the copper plate was clean.
Abroad a number of experiments have been made.
In connection with the building of the torpedo-boat Foudre, Mr. A. F. Yarrow carried on a series of experiments, the results of which he describes as follows: "With reference to corrosion from sea water, we have tried a series of experiments, extending over twelve months, and we find, provided there is no galvanic action due to other metals being in contact with aluminum, the corrosion may be taken at under 4 per cent, for aluminum for Plates about one-eighth inch thick, the surface being unpainted."[*]
This rate is not unfavorable in comparison with the usual rate for steel.
As a result of investigations of corrosion incident to the subsequent condition of the Foudre, M. Le Chatelier, Naval Constructor, French Navy, pronounced that aluminum is oxidizable in Proportion to its impurities; that salt water affects the aluminum of commerce, but not pure aluminum; that pure aluminum resists oxidation as well as gold and platinum, and is not attacked by nitric and sulphuric acids, though dissolving in alkalies and hydrochloric acid.
M. Besson, Naval Constructor, French Navy, arrived at similar conclusions after investigations in connection with the building of the Davoust for African service, stating that corrodibility diminished as the quantity of copper impurities diminished, pure aluminum being practically incorrodible, the impurities most instrumental in causing the corrosion being aluminum oxide, iron, carbon and silicon.
M. Guilloux, Naval Constructor, French Navy, designer and superintending constructor for the Vendenesse, who also inspected the Foudre after her corrosion, and who investigated the subject in conjunction with M. Minet, of the Ecole des Arts et Metiers of Paris, found that the usual assemblages of aluminum, taken at random, are liable to create batteries within themselves, and found that the more aluminum is electro-positive the better it resists salt water, and enjoined the following rules in the use of aluminum: 1. Choose aluminum as pure as possible. 2. Have the ingots mixed by fractional fusion to insure homogeneity. 3. Subject the material to galvanometric test and require it to be electro-positive to a piece already tried and found to give satisfactory resistance to corrosion. Take careful precautions during construction. Paint all surfaces and avoid absolutely all contact with copper.
In the paper in which these investigations were described, read before the Association Technique Maritime, which had been preceded by a paper on investigations in connection with the Vendenesse, M. Guilloux stated in conclusion that he regarded the metal as well adapted to marine construction, though delicate and as yet of irregular composition in production, while but slightly understood and insufficiently tried.
Experiments conducted at Neuhausen, Switzerland, in 1895, showed that pure aluminum was not attacked, while they showed that the copper alloys were badly attacked.
In connection with the application of aluminum to uses in the arts and industries ashore, various experiments have been made in the United States and abroad on its resistance to the usual agents that attack metals, noted among which experiments are those conducted by Professor Richards of Lehigh University. The uniform result has been the establishment of the fact that aluminum offers particularly great resistance, except in the case of alkalies and the chlorine group.
The experience in actual service and the experiments made, as outlined above, are inadequate to a definite and final conclusion as to the corrosion of aluminum in salt air and salt water.
The consensus, however, would lead to the following general conclusions:
1. When isolated, pure aluminum is not attacked.
2. When isolated, the usual alloys of aluminum and commercial aluminum are attacked in a measure more or less proportional to the amount or percent of the alloy or impurities. Among the alloys, copper and zinc seem the most corrodible.
3. When in contact or in communication with other metals below it in electro-chemical scale, galvanic action sets in and aluminum and its alloys are rapidly corroded. The action takes place when the contact is between different alloys of aluminum and even between different pieces of the same alloy, when not homogeneous; and there is indication that the corrosion of isolated alloys is probably due, in large measure, to the galvanic action between the particles of the two metals in the body of the alloy. Copper is again the metal whose contact causes most accentuated action, and the copper alloy is the alloy in which galvanic action is most marked.
4. The conditions of corrosion can be ameliorated by the application of coatings and coverings. The usual coatings for iron and steel, however, are not adapted to aluminum, particularly red lead. In case of special coatings, as yet prepared, special care and frequency of application are required. It would seem that the special characteristic to be sought is impermeability.
While drawing the above conclusions on corrosion, the imperfect behavior of steel and iron should be borne in mind. With full appreciation of this imperfection, however, the comparison of the two metals gives the following general results:
1. At the present stage, structural aluminum is materially more subject to corrosion than steel. The marked corrosion, however, must be attributed to galvanic action due to the high electro-positive character of aluminum, the pure metal itself, Practically incorrodible, being far ahead of steel, and to this galvanic action must be attributed the corrosion of alloys and the usual commercial aluminum where even there is no external contact with other metals, the action taking place in the body of the metal from the intimate contact of the molecules of aluminum With the molecules of the alloying metals or impurities.
2: This feature of inferiority must therefore be regarded as subject to future amelioration from increase of knowledge and selection in the preparation of the alloys and from improvement in conditions of insulation and protection. Substantial amelioration has already been found in the use of nickel for the alloy, without entailing loss of strength, while further amelioration seems promised in the use of tungsten for the alloy.
Special measures toward insulation seem not to have been taken or tested in any case.
3. The coatings used for painting steel are not effective in protecting aluminum, and the special coatings as yet prepared are but partially effective, and then only on condition of special care and frequent renewal.
4. This feature of inferiority must likewise be regarded as subject to future amelioration with further experiment and increase of knowledge. It could scarcely be expected to find a suitable coating without research, particularly when the usual coatings for steel are composed so largely of oxides of metals whose contact with aluminum sets up galvanic action.
5. The degree of importance of the inferiority of aluminum to steel in the question of corrosion varies with the conditions of exposure and is disqualifying when the exposure to salt water and spray is constant and where frequent visitation is difficult or impracticable.
The cost of maintenance and care and the length of life identify themselves, as seen above, with the question of corrosion. Without being able, evidently, to assign definite values, the cost of maintenance and care at the present moment must be taken as appreciably greater for aluminum than for steel. The cost of additional care is not of great consequence for parts easily accessible, provided the exposure is not great and the coatings applied or the other process of care are at all effective. For parts constantly exposed multiply the frequency of visitation, the additional cost is considerable, particularly where the parts are difficult of access. In such cases of exposure and difficulty of visitation, the inferior conditions of preservation reduce the length of life, which, under good conditions even, must be considered as shorter than the life of steel. This factor of cost takes on large proportions and, at the present moment, must be considered prohibitory for water-washed surfaces and parts in contact with bilge water, while still of large consequence for all outside parts, topsides, upper works, and upper deck fittings.
F.—APPLICATIONS.
With the conclusions thus arrived at for cost of maintenance and length of life and the results of calculations for strength, weight and first cost, assembled in the table adjoined, a basis exists for judging between the two metals for adaptability to the various purposes of marine construction. For the present purpose and in keeping with the necessitated method of broad treatment, examination will be limited to salient features only.
1. Adaptability for shell plating.
(a). For plating below water.
(1). Bottom plating requires, besides elastic strength for structural stresses, special ultimate resistance to dynamic strains incident to grounding or even docking or moving alongside of wharves.
While adequate to the first requirement, aluminum, as seen, is altogether lacking in the second; an aluminum bottom would be Penetrated and torn open where a steel bottom would only be deformed without perhaps springing a leak.
A torpedo explosion on the bilge or flank would shatter aluminum plating over a large area, bilging in all probabilities a larger number of compartments.
From considerations of strength, aluminum is thus unadapted for bottom plating of large vessels, unless reinforced by sheathing.
(2). Bottom plating is necessarily in constant exposure to salt water and beyond the reach of visiting except at long intervals when in dry dock. Considerations of corrosion, of care and shortness of life also unfit aluminum for bottom plating of vessels keeping the sea, unless they are sheathed.
Notwithstanding its advantages of lightness, aluminum is therefore doubly barred from use for bottom plating of unsheathed vessels keeping the sea.
(3). The application of sheathing to prevent fouling gives to steel bottoms an excess of resistance to penetration; its application to an aluminum bottom would supply the deficiency of resistance, and at the same time give protection from the contact of sea water.
Having a weight ratio of but .43, the aluminum bottom would realize a large saving, amounting in a 9000-ton vessel to about 200 tons, a large fraction of the increase of weight due to sheathing.
The cost ratio being 2.83, the increase of cost in the case considered would be about $9o,000, or about 3 per cent. of the total cost of vessel.
A 3 per cent, increase of cost is a small price to pay for a 2 per cent. saving of weight.
The bottom would still be liable to corrosion from the inside, and until experiments have been made with cement and other bilge coverings, it would not be prudent to use aluminum even for sheathed bottoms in the parts where bilge water is liable to collect.
(4). For torpedo-boats and small boats considerations of stiffness determine the scantlings for shell plating. The fiber stress of girder calculation in such cases is less than half the stress admissible. To give the same stiffness, aluminum plates would be 1.34 as thick as steel, making a weight ratio of .48, but the same weight of aluminum plating would realize 9 times the stiffness. For stiffness, therefore, aluminum offers pronounced advantages. In cases of grounding, however, to which such boats are more or less liable in their operations in shoal water, the inferiority of aluminum in dynamic resistance would be in evidence as for the case of large vessels, debarring its use for keel plates and garboards.
When navigating in fresh water and when hauled up, such craft are removed from the corroding effects of salt water and sojourn in these conditions is more or less extended. The conditions of corrosion are therefore materially ameliorated, but would still require a suitable coating or paint of good resisting qualities.
The increase in cost would be similar to the increase in the case of large vessels, not at all prohibitory.
There are therefore material advantages to be gained in the use of aluminum for the bottoms of torpedo-boats and small boats generally, where saving of weight is precious and only the absence of a suitable paint stands in the way of adaptability.
(b). For plating above water.
(1). In conditions of usual service, plating above water does not require unusual dynamical resistance found necessary for the safety of bottom plating, and the pronounced greater elastic dynamical resistance of aluminum places it perhaps ahead of steel, notwithstanding the great inferiority in ultimate dynamical resistance. In battle, however, the inferiority of aluminum would again appear in an emphasized form, in the increased wreckage and debris and multiplicity of splinters. The use of aluminum is therefore questionable in wake of gun protection and in the region of unprotected spaces occupied in battle. This is an important factor for unarmored war vessels and is serious for armored vessels, where, notwithstanding isolation of gun positions and the high degree of armor protection, the secondary battery is largely exposed, and fragments and splinters are still a menace.
The conditions of corrosion are severe just above the water line and would exclude aluminum from two or three strakes at least. For the topside above, subjected to intermittent spray and sea, the conditions of corrosion, though much less, are still serious and would require an efficient protecting coating.
The increase in cost is similar to the increase for plating below water and is not commensurate with the similar large gain or saving in weight.
(2). Fragments and splinters in battle do not enter the consideration for torpedo-boats and small boats and for mercantile vessels.
(3). There is therefore an important field for aluminum in plating above water, restricted only by the lack of a suitable coating.
2. Adaptability for framing.
Requirements of dynamic resistance exclude aluminum from use in framing behind armor and in general from all association with armor except the support of weight. They affect its use in gun positions and in other spaces occupied in battle where fragments and splinters are to be feared.
For framing elsewhere, however, the nature of its resistance would not incur disadvantage for aluminum, except to a certain extent for outer angles of frames and longitudinals.
Considerations of corrosion are against its use as outer or frame angles in the parts liable to collect bilge water, also as outer angles on longitudinals in the same regions. The conditions for the other parts are also more or less severe.
For the purpose of comparison, assuming the use for all longitudinals and transverse framing below protective deck and for half the transverse framing above the protective deck, the saving in weight in a 9000-ton vessel of ample freeboard would be about as follows, with weight ratio .48 for shapes and .43 for plates.
Total saving about 116 tons. With cost ratio of 2.9 for plates and 5 for shapes, the additional cost would be about $98,000, $69,000 additional for shapes and $29,000 additional for plates.
It is to be noted that the shapes realize only 56 tons of the 116 tons saved, while they entail $69,000 out of $98,000 increase of cost, illustrating the general fact of the smaller advantage to be gained in the use of aluminum for shapes than is to be gained in the use for plates.
In the present case, as pointed out, the outer angles are additionally subjected to severe conditions of corrosion. If therefore these remain of steel, the saving in weight would be about 16 tons less and the increase of cost would be reduced by about $20,000.
Considering the smaller advantage of weight, the larger increase of cost, the severer conditions for corrosion, and the lesser adaptability of resistance, it would appear advantageous to have the outer angles of steel even in the case of the adoption of aluminum for the plates and inner angles.
For these latter plates and angles decided advantage is to be gained in the use of aluminum when a suitable coating is found. Until this time, however, such use would not be prudent in view of the conditions of the double bottom and difficulty of access.
For framing below the protective deck forward and abaft the double bottom, and for framing above the protective deck, where not associated with armor, and where there is no special menace in battle from fragments and splinters, aluminum can be used With advantage in the present stage of progress, provided, as is assumed throughout, that use is made of an alloy other than copper, and that due attention is paid to preservation.
For torpedo-boats and for small boats generally the conditions of corrosion of frames are not severe, and the frames are more or less accessible, excepting the lower parts of frames of torpedo-boats. The nature of its resistance being suitable, aluminum is therefore adaptable. General adoption for this purpose, however, should also be preceded by experiments to determine the coating best suited for preservation, while it should be borne in mind that the gain in weight of about one-half entails an increase of five times in cost.
3. Adaptability for inner bottom.
The nature of aluminum's resistance is suitable for inner bottom plating where the conditions of corrosion are not severe, due regard being taken to the conditions of the underside and the difficulty of access. With a coating of fair efficiency and with due attention, aluminum offers decided advantages for general adoption for inner bottoms. Taking the case of a 90o0-ton vessel, the gain in weight with plates of equal stiffness would be about 30 tons, and the increase in cost would be about $16,000.
4. Adaptability for bulkheads.
The integrity of bulkheads is undermined as a rule by distortion destroying water-tightness, while rarely, if ever, is the metal called upon to exert its ultimate strength of resistance. The superior stiffness and greater elastic resistance of aluminum mark it therefore for special adaptability for bulkhead purposes, for both plating and stiffeners.
Standing vertically as it does, with ease of access and without exposure of any kind, the conditions for preventing corrosion are peculiarly favorable.
Aluminum therefore is eminently suitable for bulkhead purposes for all classes of vessels.
5. Adaptability for decks.
For reasons pointed out above, aluminum is debarred from association with the protective deck. The nature of its resistance, however, is suitable for other decks, both for beams and Plating, exception being made for stringers and tie plates, reservation being made also for considerations of fragments and 'splinters in battle as pointed out above.
For beams, however, with the present conditions of manufacture, the sizes required for large vessels, for which there has yet been no demand, could probably be produced only with increased difficulty, though for the present purpose it will be assumed that they could be produced at the price quoted above for shapes.
Conditions of corrosion would exclude the use for the upper deck unless the plating were covered by wood flat. As a matter of fact such a wood flat is found, as a rule, on the upper deck of war vessels where the deck is of steel. All other decks would require efficient linoleum or other covering on top and an efficient coating on underside. For structural purposes the deck stringers would remain of steel.
6. Adaptability for other hull work.
(1). For casings and trunks the same advantageous conditions are offered for aluminum as pointed out in the case of bulkheads. For a 9000-ton vessel the saving in weight would be about 45 tons, about 51 per cent. of the weight in steel, with an increase of cost of about $30,000, about 254 times the cost in steel.
(2). For small trunks and ducts, coaling trunks, ventilator trunks, forced draft ducts, ammunition hoist trunks, chain lockers, blower casings, the same conditions hold; the saving in weight would be about 32 tons, and the increase in cost about $21,000, bearing about the same ratios to total weight and cost in steel as found for casings and trunks.
(3). Similarly for hammock berthing where the saving in weight would be about 14 tons, and the increase in cost about $9000, bearing about the same ratios to total weight and cost in steel.
(4). For metal ceilings inside the same conditions hold, giving a saving of about 6 tons with an increase of cost of about $4000, bearing about the same ratios to total weight and cost in steel.
It should be remarked that the greater conductivity of aluminum would increase the condensation, requiring special provision against same in living spaces.
7. Adaptability for hull fittings.
(1). For the ventilating system, the conditions for corrosion are not severe and there are no special requirements for resistance. Aluminum is therefore suited to the air ducts and fittings, and the pipes and cowls, into which forms it can be readily made and is easily worked. On the vessel taken for the comparison the saving in weight would be about 20 tons, with an increase of cost of only about $8000, the cost ratio being taken at 1.24. About 3 1/2 tons are saved in the copper and brass cowls, rims and hoods, without increase of cost.
For the cowls, too, the lighter weight affords greater ease of manipulation for trimming to wind.
(2). For metal doors, water-tight and non-water-tight, the advantages of aluminum are in special evidence. For watertight doors, the stresses are similar to those of bulkheads, the main consideration being stiffness and resistance to deformation. The distinctive superiority, however, lies in the greater ease of Opening and closing afforded by the lighter weight. On the vessel in question the saving in weight would be about 18 tons and the increase of cost but about $6000. There would be advantage for the substitutions for some wooden doors, as to staterooms, where lightness is also specially desired.
(3). For hatches (other than armored), man-hole covers and frames, the same considerations hold. The saving in weight would be about 11 tons, with an increase in cost of about $4000.
(4). For torpedo ports and coaling ports, the special advantage of ease of handling is again in evidence, though the conditions of corrosion would require an effective coating on the outside. The saving in weight would be about 5 tons and the increase of cost about $2000.
(5). For dead light, air port, and deck light frames and casings, east aluminum would be well suited provided due attention is given to consideration of corrosion, proper care in selection of material of castings, and application of effective coating. The saving of weight over the brass castings would be about 15 tons Without any considerable increase of cost.
(6). For metal ladders and gratings, ease of handling due to lightness gives a distinct advantage, and conditions of corrosion are not severe. The saving of weight would be about 3 tons and increase of cost about $1000. There would also be advantage in many cases in the substitution of aluminum for wood gratings.
(7). For masts and spars the advantage of lightness is in special evidence as reducing high weights, and the conditions of corrosion are not severe. Aluminum is therefore well adapted for usual service where sails are not carried and unusual forces are not to be resisted. It is to be noted, however, that in battle an aluminum lower mast would be more likely to be shattered and boat drop its charge of military tops, etc. For the lower booms, or booms, lightness offers additional advantage for rigging in and out.
The substitution in the case of a vessel carrying two military masts of usual development would be about 14 tons, the increase of cost about $7000.
(8). Among additional miscellaneous fittings for the application of aluminum may be mentioned fresh water tanks, galley outfit, urniture, ammunition boxes, binnacles, lanterns, etc.
Reference has been previously made to the fact of aluminum's being largely debarred from boiler and engine application on account of the overthrow of its physical properties by heat, even at comparatively low temperature. It should be pointed out, on the other hand, that this obstacle is not incurred in a number of applications in the engine and fire rooms, such for instance as the parquets or floors, envelopes of boilers and condensers, condenser tubes, etc. In connection with the use for condenser tubes it would be necessary to avoid the use of alkalies like soda in cleaning. In the above and in many other applications the lightness of aluminum would be in large advantage, particularly for reciprocating parts. In other applications, to parts of machinery where unusual forces are not to be feared, where the oft repeated forces are well known, the high elastic dynamic resistance would in addition be of decided advantage. For the present purpose, however, this field of application is not investigated.
(9). The above applications, assembled, are as follows:
First, where, at the present stage and under the present condition of manufacture, aluminum could be used to advantage, provided a suitable alloy other than copper is used, and provided due care and attention are given to preservation.
Thus, at the present state of manufacture and with present means of preservation, there could be realized with safety on a vessel of 9o00 tons a saving of about 380 tons with an additional expenditure of about $250,000, or an economy of about 4 4 per cent, of the total weight of vessel with about 8 1/3 per cent. Entailed increase of cost. The relative advantage is most marked in the case of hull fittings, where the saving of weight is about 74 per cent, of total weight of hull fittings, and the entailed increase of cost is only about 8 1/2 per cent. of total cost of hull fittings.
Second, where aluminum can be used with advantage as soon as experiment finds an efficient coating against corrosion.
Thus, as soon as an efficient preservative coating is found, a further field will be opened up where with a 9000-ton vessel an additional saving of 380 tons could be realized by an increase of cost of about $57o,00o, or a saving of about 872 per cent. of total weight and an increase of about 8 ½ per cent. of total cost.
When thus occupying its whole legitimate field in hull construction, the use of aluminum would realize, in a 9000-ton vessel, a saving of weight of about 760 tons with an entailed increase of cost of about $51o,000, or a saving of about 8Y2 per cent, of total weight with an increase of about 17 per cent, of total cost.
It should be recalled that the above results apply to a vessel of war, and for the present purpose it will suffice to point out that for a merchant vessel, where conditions of battle are not taken account of, the application would be larger.
G.—SUMMATION--CONCLUSIONS.
The above comparisons lead to the following results:
Comparison for Strength and Weight.
1. In simple tension, aluminum, which is about 1/3 as heavy as steel, has about 2/3 of the ultimate and about it of the elastic resistance.
In simple compression and shearing the ratios are slightly smaller.
2. In bending, aluminum bars of square section having the same weight as steel give about 2.9 times the ultimate strength and about 4.5 times the elastic moment of resistance, and are about 3 times as stiff.
Aluminum plates of equal weight give about 5.1 times the ultimate and about 7.8 times the elastic moment of resistance, and are about 9 times as stiff.
Aluminum shapes of proportioned dimensions of equal weight give for I beams about 2.9 times the ultimate and about 4.5 times the elastic moment and about 3.1 times the stiffness, and for angles about 2.4 times the ultimate and about 3.6 times the elastic moment, and about 2.3 times the stiffness.
3. In elastic elongation, aluminum gives about 2.8 times the elongation of steel with a modulus of elasticity of about 53 of steel. For elongation beyond the elastic limit, aluminum is incomparably below steel, the ratio being smaller as the length increases.
The dynamic resistance of aluminum in tension within the elastic limit is, therefore, about 2.6 times the resistance of steel Per unit of cross section, and is about 7.8 times the resistance for equal weight.
Beyond the elastic limit the dynamic resistance of aluminum cannot be compared with the resistance of steel.
Comparison for Cost.
1. To realize the same resistance, plate work in aluminum costs, in general, about 2.8 times as much as steel in hull work and about 1.2 times as much in hull fittings; angle work and work in other shapes cost, in general, about 5 times as much in hull work and about 1.7 times as much in hull fittings.
Cast fittings in aluminum cost about 1.5 times as much as in steel and about the same as in brass.
In all of these cases the weight for aluminum construction is less than half the weight for steel and about y3 the weight for brass.
2. The cost of maintenance and care is at present substantially greater for aluminum construction than for steel construction, and increases in proportion to the exposure to corrosion, which becomes exaggerated where conditions favor galvanic action.
3. The length of life of aluminum construction under favorable conditions must be regarded at present as substantially shorter than the length of life of steel construction, on account of pronounced tendency to corrosion. This tendency has been found to be due in most part to galvanic action, largely caused by the alloy or impurities in the metal, an alloy being necessary to realize good results of strength. Of the alloys tried, the copper alloy has given the worst results for corrosion.
As yet a suitable protecting coating has not been found and the field is calling for further scientific experiment.
The cases of the employ of aluminum have been unfortunate in results of corrosion, but they have been incomplete and the conditions, upon examination, have been found to have been extremely severe.
With a properly chosen alloy, like the nickel alloy, and with proper care, aluminum can be safely used where there is not direct exposure to salt water and spray, and the further extent of the advantageous use to fields where the exposure is not specially severe is only held back by the lack of an efficient protective coating.
Applications.
The results of the comparisons for strength and weight and for cost lead to the conclusion that at present aluminum is adapted for use in hull work for bulkheads, casings and trunks, small trunks and ducts, hammock berthing and metal ceiling, and for use in hull fittings for parts of ventilation system, for metal doors, hatches, torpedo ports and coaling ports, metal ladders and gratings, masts and spars, this adoption in the case of a 9030- ton vessel realizing a saving in weight of about 380 tons at an increase of cost of about $25o,000.
The same results lead to the conclusion that as soon as an efficient coating is found aluminum will be further adapted for the bottom plating of sheathed vessels, for the bottom and topside plating of small vessels, part of the topside plating of large vessels, for bottom and topside framing of small vessels, for topside framing of large vessels, for the bottom framing of large vessels except outer angles in double bottom, for inner bottom plating, and deck plating, and for dead light, air port and deck light frames and casings, realizing by this adoption in a 9000-ton vessel a saving in weight of about 380 tons at an increase of cost of about $26o,000.
It is to be remarked that in the above applications it is assumed that galvanic action does not set in from the contact of aluminum and steel, an assumption apparently justified by experience thus far; but in course of time it is largely probable that appreciable action would set in, if some insulating provision were not made in the joints between the two metals. It is not believed, however, that such insulation provision would be impracticable.
It may be recalled also, as stated in the outset, that performances and homogeneity of aluminum as taken are somewhat ahead of the present stage of manufacture, and that the applications have been extended to dimensions and scantlings not yet commercially turned out.
Moreover, it should not be overlooked that the element of cost in the maintenance and care of aluminum construction and the length of life are not well determined and are difficult to evaluate on account of the limited experience.
The results arrived at are thus to be taken in connection with the limitations necessarily imposed by the fact of the field being essentially new.
In summation, and in conclusion, aluminum has incontestable virtues as a structural material. Its great elastic elongation and resistance within the elastic limit places it far ahead of steel for resisting usual, well determined and repeated dynamic forces, While its great comparative lightness marks it for marine construction. On the other hand it has serious defects. An excessively low elongation beyond the elastic limit unfits it entirely for use where liable to be subjected to violent and unknown dynamic forces; temperatures beyond atmospheric undermine its physical Properties; while, notwithstanding an innate superior resistance When pure to the attack of corroding agents, the high position on the electro-chemical scale causing excessive tendency to galvanic action, places a severe obstacle in the way of adoption where ex- Posed to salt water and spray, particularly in the case of alloys, in which form alone the metal exhibits its best physical properties. This last serious defect, however, must be considered as subject to constant amelioration with increase of knowledge and experiment in precautions and higher perfection in manufacture.
Thus, while this new metal has an important field in marine construction, an important field now ready for occupation, and additional fields awaiting only the improvement in conditions for resisting galvanic action, these fields are essentially limited, and the larger domains are shut out by impassable barriers.
The early optimist who inferred all virtues from a single virtue, and the later reactionist who pronounced general unfitness from a few partial trials, were both wide of the mark. The metal is not utopian, but it has nevertheless beyond question an important mission for the serious marine architect, who is only waiting further improvement in manufacture and reduction in cost and further amelioration in conditions of corrosion.
For the naval architect of our own country, for our country itself, the question has a special significance.
The maintenance of a strong commissioned naval force must be our country's policy for taking its destined part of international greatness in regulating the common affairs of the planet, but our Position and the spirit of the nation mark our naval policy specially for a great force kept economically in reserve, commissioned illy periodically for drill purposes.
In a state of reserve the conditions of corrosion are greatly ameliorated. The vessels seek and lie in fresh water; the torpedo boats and small boats, which do not seek fresh water, are hauled up under sheds. Under these conditions the great obstacle of corrosion is largely removed from aluminum's path. Indeed, aluminum appears to be superior to steel in the resistance to the corroding effects of atmospheric exposure and of fresh water.
The question becomes more significant where account is taken of the great natural facilities and possibilities of our coast line for fresh water basins of large expanse for taking vessels of all sizes. It takes on a still more significant aspect when it is recognized that nature in the inland routes along the coast has marked small craft as our great second line of defense, while, in the inland waters of great rivers and great lakes in communication with the sea, she has provided immeasurable possibilities for the construction and maintenance of these craft.
Torpedo-boats which are thus marked for a great natural economical branch of national defense form now the least developed arm of our navy.
There therefore lies ahead, inevitably, a vast programme of torpedo-boat construction, for which every advantage of materials of construction should be earnestly sought. Fortunately for the nation this branch of defense admits of rapid growth and may be expected to have large expansion in the near future. Indeed, the time is not very far distant when, with treaty restrictions abrogated, we shall see on the great lakes, vast flotillas of torpedo-boats, lying for most of the year in economical reserve free from corrosion. Periodically, they will be commissioned for drill purposes, and from time to time will sally forth to the seaboard for mobilization and exercise in the operations of coast defense.
We would realize thus, at a minimum cost and a minimum turning away of the nation's energies from the channels of production, a great power, tranquil in time of peace and good will, irresistible for defense in time of war.
(Discussions are requested, to be published in No. 84.)
[*] See paper by Mr. Yarrow in the Transactions of Naval Achitects, vol. xxxvi, 1895.