Considering the two main factors of resistance, namely, Skin Resistance and Wave Resistance, experience shows that for large vessels of very low speed the Skin Resistance may approach 90 per cent of the total. For ordinary vessels of moderate speed, it is usually between 70 and 80 per cent of the total.—D. W. Taylor.
Ship's bottom paint, and the prevention of fouling on the bottom of sea-going ships, are subjects of considerable importance to the navy, not only because of the large annual expense in painting the ships and the desirability of reducing such expense, but on account of battle efficiency, as affected by the condition of the ship's bottom. The recent interest in steaming repetition will direct attention to this matter, and while it may serve to increase the importance of the question, it will at least under it of more personal interest to officers. For the last reason justification of this present paper is sought, and it is offered with the idea of informing the service as to the general questions affecting ship's bottom paint, especially, the particular phases affecting its use on naval vessels, and the causes that led up to the manufacture of ship's bottom paints at navy yards, the methods followed in developing and testing formulae and the results obtained from the use of the government paint.
The effect of a foul bottom on the speed, maneuvering qualities and coal consumption of a ship is well known, nevertheless a ingle remarkable instance will be cited as an illustration of what may be expected to occur. Recently, an armored cruiser painted it previous docking with a standard commercial ship's bottom paint, was placed in dry dock on the west coast, after having been out of dock 16 months, and was found to be very foul. An estimate of the total weight of barnacles and other growths removed was given as 600 tons, and when undocked the vessel's draft was 4 ½ inches less than when docked, other conditions being the same. This was a cruising ship, the itinerary of which since prior docking, had included cruises to South American ports and the Samoan Islands. Other similar cases where the speed and coal consumption of vessels have been affected considerably by foul bottoms are of common occurrence, and are well known to officers generally.
The question of protecting the underwater bodies of sea-going ships has always been vital, and since the use of steel for hulls has become general, a suitable paint for this purpose has been in demand. Various manufacturers offer commercially, generally under proprietary names, so-called ship’s bottom paints and compositions, which are designed to effect the double purpose of protecting the bottom plating from the corrosive action of sea-water, and, also, of preventing the attaching of the various marine growths, such as grass, barnacles, hydroids, etc. The necessity for the periodic docking of ships, often at intervals of less than 6 months, bears witness to the fact that so far no satisfactory ship’s bottom paint has been produced: those in general use represent the best available, but all leave much to be desired.
The composition of the various commercial ship’s bottom paints, their ingredients, method of manufacture and action are screened by an affected mystery as “trade secrets,” by those interested in their sale—this fact more than any other probably accounts for the vagueness existing in the minds of many seafaring people on this important subject. The question, however, is one that appeals to the popular mind, especially to inventors, and patents are taken out, not only for paint compositions, but for various mechanical devices for removing or preventing fouling. Mechanical removal of barnacles without docking is, of course, at the best only a temporary expedient, as the metal thus left unprotected quickly fouls again, to say nothing of the corrosion that must be checked to prevent serious damage. The Navy Department is frequently constrained to make tests of ship’s bottom paints offered by persons who are convinced that they have at last solved the difficulties. Various forms of mechanical devices for preventing fouling have been tested also, but so far, as the continued use of paint shows, without success in improving the situation.
Work toward improving those ship’s bottom compositions that give the most satisfactory results is done, generally, by interested producers, who utilize the available results in the improvement of their own product, but suppress all data that might be of advantage to competitors. This may explain the fact that literature on the subject of ship's bottom paints is generally meager, largely theoretical and often misleading.
As a general rule, bottoms of ships are painted with two different kinds of bottom paint, the anticorrosive, applied usually in two coats next to the metal, and the antifouling, applied in one coat over the anticorrosive. The function of the anticorrosive is to protect the metal, not only from the corrosive effect, which is very great, of the sea-water, but from the corrosive action of the poison which is included in most of the antifouling paints to kill marine growths. Antifouling paints may be divided generally into two classes, the varnish or "poison paints," which comprise the great majority, and the grease or wax paints, which are of the consistency of soft soap and must be heated to permit of being applied.
The commercial paints consist generally of a varnish made up largely with ordinary resin, in a vehicle consisting of the higher distilling hydrocarbons, such as benzene or naphtha, and in small quantities of turpentine and linseed oil. The pigments used for the anticorrosive paint are iron oxide, talc, china clay and zinc oxide. The antifouling varnish paints are generally similar in composition to the anticorrosive, but have, in addition, certain poisonous ingredients, the most usual poisons being the red oxide of mercury, copper oxide, arsenic, calomel and corrosive sublimate.
The commoner antifouling grease paints consist simply of a copper soap and a small percentage of copper oxide. The anticorrosive paints used under the grease paints are the same generally as those used with the varnish paints.
In order that the similarity of the various better-known brands of ship's bottom paints may be judged, a brief statement is given of the characteristics of several of these, as determined by chemical analysis by a navy yard chemist:
Comparative Analyses of Various Ship’s Bottom Paints
"Paint A."
Anticorrosive: The pigment contains oxides of zinc and iron, with carbonate of lime in a vehicle containing benzene, resin, linseed oil and turpentine.
Antifouling: The pigment contains oxides of mercury, zinc, and iron with carbonate of lime and silica in a vehicle containing benzene, resin and linseed oil.
"Paint B."
Anticorrosive: The pigment contains oxides of zinc and iron, calcium carbonate, and silica in a vehicle containing benzene, resin and linseed oil.
Antifouling (a): The pigment contains oxides of mercury, zinc and iron with silica in a vehicle containing zinc soap, tar, resin, linseed oil and benzene. Antifouling (b): The pigment contains cuprous oxide, mercuric oxide and arsenic sulphide in a vehicle containing varnish resins, benzene and nitro-benzol.
"Paint C."
Anticorrosive: The pigment contains iron oxide, with a silicious earth similar to kaolin, and contains small quantities of aluminum, magnesium oxides, in a vehicle containing a mixture of benzol and coal tar naphtha with resin and zinc soap.
Antifouling: The pigment contains a mixture of silicious earth, similar to kaolin, with iron oxide and oxides of copper and mercury in a vehicle containing coal tar naphtha and benzol with resin, copper soap and zinc soap.
"Paint D."
Anticorrosive: The pigment contains an iron oxide earth and silicious matter similar to china clay, with a small percentage of zinc oxide, in a vehicle containing coal tar naphtha and light petroleum hydrocarbons with resin and small amounts of zinc soaps.
Antifouling: The pigment contains an iron oxide earth, silicious matter similar to china clay, cuprous oxide and zinc white, and is free from mercury, in a vehicle containing coal tar naphtha and light petroleum hydrocarbons with resin and small amounts of zinc soaps.
"Paint E."
Anticorrosive: The pigment contains an iron oxide earth, zinc white, silicious matter similar to china clay and cuprous oxide, in a vehicle of coal tar naphtha with resin and zinc linoleate.
Antifouling: The pigment contains iron oxide earth, zinc oxide, cuprous oxide, graphite and silicious matter similar to talc in a vehicle of coal tar naphtha, resin and a zinc soap.
"Paint F."
Anticorrosive: The pigment contains oxides of iron and zinc, silica, alumina and lime in a vehicle of linseed oil and a volatile hydrocarbonate.
Antifouling: The pigment contains iron, zinc and copper oxides, silica, alumina and lime in a vehicle containing tar oil, turpentine and wood spirit.
"Paint G."
Anticorrosive: The pigment contains metallic brown in a vehicle of linseed oil, wood tar, wood alcohol and resins.
Antifouling: The pigment contains oxides of copper, mercury and
iron, with calcium sulphate in a vehicle containing copper and
mercury soaps, linseed oil and benzene.
"Paint H."
Anticorrosive: The pigment contains oxides of iron and manganese
with lime in a vehicle containing linseed oil, hydrocarbons and
nitro-benzol.
Antifouling: A green copper soap containing about 9 per cent of
copper oxide.
"Paint I."
Anticorrosive: The pigment contains metallic brown (containing about 56 per cent of iron oxide) in a vehicle containing zinc soap, benzene, aniline oil, tar and resins.
Antifouling, green: The pigment contains about 90 per cent of Paris green (copper aceto-arsenic) and about 10 per cent of calomel in a vehicle of lead soap, aniline oil and a thick resin varnish.
It should be noted that "Paint H" and "Paint I" are of the type of so-called soap or grease paints and are applied hot.
Action of Ship’s Bottom Paints
There is a question as to the exact nature of the action of antifouling paints in preventing marine growths, the most probable explanation appears to be, that in the case of the poison Mints, the spores are killed by the soluble chlorides formed by At action of sea-water on the "poison" before they are able to attach themselves. Dead barnacles often are seen attached to the bottom of ships, and often there are evidences that others have dropped off. It does not appear likely, however, that this is due to the action of the paint, but to other causes, presumably the water in which the ships have been lying before being docked. In the case of the grease paints, the familiar exfoliation theory is generally advanced. That does not appear tenable, as the characteristics of the paint are not such as to support it, even if we do admit that it is correct in the case of copper sheathing. It seems likely that these paints, due to their softness and slippery surface, simply render the attachment of growths difficult. In any event, the popularity of this class of paints has decreased considerably, due in a measure probably to the high cost of applying them.
There is an undoubted variation in the efficiency of paints, depending on the waters, the season of the year, etc. A paint that may give excellent results at one time, may, in other waters or at other seasons in the same waters, fail entirely to protect from fouling. Furthermore, there is a difference in result, due to conditions not understood which make the barnacle crop vary from year to year. The apparent results are affected frequently by the vessel's stay at the dockyard prior to docking, as the water may be fresh, as at Philadelphia, or it may contain foreign substances, as at New York, in both of which cases the barnacles die and frequently fall off.
Since the 1900 edition, the Navy Regulations have required that, wherever practicable, paint of the same nature as that previously used shall be employed on the bottom of naval vessels. This requirement was based on the idea, which appears to be to some extent erroneous, that different kinds of paint of differing compositions affect each other deleteriously, and that the best results can be obtained only when different kinds are not used on the same bottom. This idea was so firmly fixed that this provision of the regulations was interpreted by one Secretary of the Navy to require that the same brand should be used wherever practicable, and instructions to this end were issued to the paint boards at all navy yards. This resulted in requiring the purchase, at manufacturers' own prices named without competition, of the necessary supplies of various brands of ship-bottom paints. It was left to the shipbuilder to apply any one of the approved brands of paint to the bottom of a vessel building under contract, and the subsequent use of whatever brand he chose became in this way imposed to some extent on the Navy Department. The conditions resulting from this practice became intolerable, as the prices paid for supplies of ship's bottom paint purchased without competition were excessive, and manufacturers of other ship's bottom paints than those commonly approved and used became insistent in their demands for recognition and to be given a chance to compete for the ship's bottom paint contracts.
Realization of the undesirable features of these conditions and the wish to remedy them, coupled with the information that patent rights on certain proprietary formulae for ship's bottom paints had expired and thus become public property, led the department to the decision in 1906, to experiment in the development and manufacture at a navy yard of a suitable ship's bottom paint for naval purposes. With this in view, experiments were undertaken simultaneously at the navy yards, Norfolk and New York: and a vast amount of work was done in experimentation on various compositions.
At Norfolk a number of formulae were developed, most of them involving the use of a varnish vehicle made with alcohol and shellac. These were tested out primarily by application to steel plates for submergence along the water front. Those which gave the best results in this test were tested further by being applied in patches to the bottom of several coal barges, along with one or more of the standard proprietary brands, to determine whether the results obtained from the paints under test were comparable with those that would be obtained from the paints previously used. In this manner, by a process of elimination, the formula for the most efficient ship's bottom paint was selected from the large number that were tried. The bottom of a collier was then painted with this paint and, the result obtained proving satisfactory, it was decided to apply paint of this composition to portions of the bottoms of two of the battleships that were then about to start on the cruise around the world with the fleet.
It is a general rule of the Navy Department in applying two kinds of ship's bottom paints to the bottom of a vessel for comparison, to divide the bottom into four quarters, each of the kinds of paint being applied to the forward quarter on one side and the after quarter on the other side. This is to ensure that both paints will be subjected to the same conditions, as frequently one side is more exposed to fouling or corrosion than the other.
The Norfolk paint was applied in this manner to one-half of each side of the U. S. S. Minnesota and the U. S. S. Kentucky, the other half of each being painted with the proprietary paint which had been applied previously to each vessel. In this way, a direct comparative test of the quality of the Norfolk paint was obtained with two approved brands of proprietary paint. At the docking of the vessels on the west coast, the condition of the portions coated with the Norfolk paint was found to be most satisfactory and compared favorably with the portions covered by the proprietary paints, as well as with the condition of the bottoms of other vessels of the fleet. The bottoms of the Minnesota and Kentucky were repainted as before to continue the experiment. Upon the return of the fleet to home waters, the Minnesota only was docked, the Kentucky being laid up in ordinary. The results in the case of the Minnesota, coupled with previous tests, were considered to be sufficiently conclusive to warrant an extension of the use of the Norfolk paint to the bottoms of other vessels, although the comparative tests between it and other proprietary paints were continued on a number of battleships in the manner referred to above.
The Norfolk paint, therefore, was applied at the spring docking in 1909, to the entire bottoms of the Minnesota and Louisiana, and to portions of the bottoms of the Connecticut, Nebraska, Georgia, Mississippi, Idaho, New Jersey, Missouri, Vermont, Virginia, North Carolina, Montana, Wisconsin and New Hampshire.
At the fall docking in 1909 of the battleship fleet, the Norfolk paint was found to have given results quite as good and in many cases better than the proprietary paints with which it was in comparison and, with this in view, the Department ordered the still further extension of the use of the government paint. The comparative tests were continued only on the New Hampshire, Wisconsin, New Jersey, Rhode Island, Connecticut, Nebraska and Mississippi, other vessels having the Norfolk paint applied to their entire bottoms. Continued good reports being received as to the results from the Norfolk paint, at the spring docking in 1910, the number of ships on which the proprietary paints were used was still further reduced, and at the fall docking in 1910, the Department directed the discontinuance of comparative tests of the character referred to, except in such special cases as might arise from time to time.
This action amounted in effect to the adoption for general use on naval vessels of the ship's bottom paint developed and largely manufactured at the Norfolk Navy Yard. At the present time, practically all naval vessels have their bottoms so painted, and this fact appears to justify a discussion of its composition, characteristics, methods of manufacture and application, cost of production and advantages derived from its use.
Composition and Characteristics
As has been noted, the paint consists of a varnish vehicle of shellac in alcohol, with the addition of small percentages of turpentine and pine-tar oil. The pigment for the anticorrosive consists of dry metallic zinc dust and dry white zinc oxide, the exact ingredients for making 10 gallons of the anticorrosive paint being as follows:
7 ¼ gallons grain alcohol.
7-9/10 pounds gum shellac.
3/5 gallon turpentine.
3/5 gallon pine-tar oil.
9 ½ pounds metallic zinc, dry.
28 ½ pounds white zinc oxide, dry.
The pigment for the antifouling consists of dry white zinc oxide, Indian red and red oxide of mercury, the exact ingredients for making 10 gallons of antifouling paint being as follows:
6 gallons grain alcohol.
13 ¾ pounds gum shellac
1 gallon pine-tar oil.
1 gallon turpentine.
13 ¾ pounds white zinc oxide, dry.
13 ¾ pounds Indian red.
4 ¾ pounds red oxide of mercury, dry.
In mixing the paint in quantities, the requisite amounts of alcohol and shellac are dumped into the shellac cutter and the carter turned for about four hours, and allowed to stand over night. The mixture is then drawn into large change tanks and the other liquids added. The dry ingredients are mixed separately and ground through the paint mills with a small quantity of the liquids and the mixture is added to the bulk of the liquid vehicle in the change tank and stirred to ensure thorough mixing. The paint is put into 10-gallon steel drums and each full drum is weighed to assure that the proper amount of paint is contained. The drums are sealed carefully to prevent loss by evaporation of the alcohol.
The anticorrosive paint resulting is of a light gray color, somewhat thin. The antifouling paint is thicker and of a dark red color. In both of these paints the pigment has a tendency to settle and for that reason care must be taken to ensure the thorough stirring of the paint before use. Due to the affinity of alcohol for water and to the fact that its addition to the paint causes the shellac to precipitate, great care must be exercised to prevent water from getting into the drums or paint buckets. If the bottom of the ship is very wet, it is necessary that free water he wiped off before applying the paint.
Before the paint is applied to the bottom of a vessel, all fouling matter and loose paint should be removed. Old paint that adheres need not be removed, except that if grease paints have been used all such paint must be removed, as the Norfolk paint will not adhere to it.
Cost of Production
The cost of production of the Norfolk paint is fixed by the cost of the raw ingredients, which is subject to some variation. For example, the shellac has varied from 14 cents per pound to 17 ¾ cents, the price on the last annual contract which covered 500,000 pounds. Similarly, the cost of the alcohol, which is obtained tax free, varies somewhat, the price averaging about 35 cents per gallon. The other ingredients vary in price but little. The 10-gallon drums cost about $1.50 each and can be manufactured at the Norfolk yard at considerably less cost than if purchased. They can be used repeatedly, so that their cost is distributed over a number of gallons of paint. The labor charges for the manufacture of the paint do not exceed 3 ½ cents per gallon.
Advantages Through the Use of Government Paint
The advantages derived by the navy through the use of ship's bottom paint of its own manufacture are very considerable, and. while the considerations which impelled the Navy Department were largely pecuniary, other advantages have developed. The pecuniary advantages may be stated briefly. Estimates made in 1910 of the cost of paint for the bottoms of all vessels on the navy list, using the kinds of proprietary brands of paint that were purchased usually prior to 1908 and distributed among the ships in the proportions of each brand then customary and at the prices then current, show that the cost of the paint for a single painting of the bottoms of all vessels of the navy, not including coal barges, etc., under the conditions noted, would have been somewhat more than $100,000. The cost of an equal amount of the Norfolk ship's bottom paint at the prevailing cost of manufacture would be less than $33,000. As a majority of the vessels of the navy are painted twice a year, it will be seen that the annual saving to the government by this means at the present time is probably not less than $100,000 annually. It should be noted, however, that largely as a result of the government entering the field with its own paint, the prices asked for ship's bottom paint by various firms previously supplying the navy, have been so reduced that if for expediency or some other reason the Navy Department decided in the future to purchase all or a portion of its ship's bottom paint, there still would remain an appreciable saving to be credited to the Norfolk paint.
Another advantage besides the pecuniary one which the navy derives from the manufacture of its ship's bottom paint is the elimination of delay frequently incident upon the purchase and delivery of articles of this character. The materials from which the Norfolk paint now is manufactured are of a character readily obtainable and some of them are usually in stock at any navy yard. This permits of prompt production of ship's bottom paint as required. The capacity of the plant at the navy yard, Norfolk, is not less than 500 gallons per day of 8 hours, or 1500 gallons if working in three shifts. So far, no other yard, except Cavite, has been authorized to manufacture this paint, but, in case of necessity, there is nothing to prevent any of the large navy yards from doing so. This paint is manufactured and successfully used at the naval station, Cavite, and considerable advantage has been derived from this fact, in rendering unnecessary the shipment at periodic intervals of large quantities of ship bottom paint, which, when stored, is subject to deterioration. The use of the Norfolk paint on vessels in these waters has been attended with uniform success, a report received in November, 1910, stating that the Norfolk paint had given better results than any other kind of ship's bottom paint tried. As those waters cause considerable fouling, it is obviously of great advantage to use an efficient bottom paint. The facilities for the manufacture of the paint at Cavite are good, and the output can be made as high as 1000 gallons a day. This, combined with the capacity of the floating dry dock Dewey for rapid docking of vessels, would render possible the prompt docking of a fleet in these waters in cases of emergency. Similar satisfactory results have been obtained in the waters at Honolulu, which are well known to cause excessive fouling.
The navy derives still further advantage from manufacturing its own paint due to the increased knowledge of the properties and effects of ship's bottom paints and their various ingredients gained from the experiments conducted in that connection. The government has already in its employ at various navy yards skillful chemists, laboratorians and painters. The abilities of these persons are thus rendered available for experimenting on and improving the ship's bottom paints. As has been noted, experiments heretofore conducted along these lines have been carried out by persons interested in some particular brand of paint. Now that the Navy Department has taken up this matter, undoubted benefit will be derived, not only to the navy, but also to the shipping interests generally, and it is not unreasonable to hope that the ultimate result may be an ideal ship's bottom paint, permitting a vessel to remain in the water for several years without fouling.
Objections have been raised as to the propriety of the government undertaking the manufacture of a commercial article, such as ship's bottom paint, and thus entering the field in competition with private firms. No justification seems necessary in addition to the facts already pointed out. However, it should be remembered that manufacture of ship's bottom paint consists merely of mixing raw ingredients which are purchased. Each navy yard is already equipped with adequate machinery for this purpose, and actually does of necessity mix paints for various other purposes. Additional work that can, in reason, be given to the paint mixers increases their efficiency and that of the plant. Private shipyards generally have paint mixing plants similar to those in navy yards, though naturally much smaller. At least one such private yard takes advantage of its facilities for the manufacture of ship's bottom paint for use on vessels docking in its dry docks. The navy is the largest consumer of paint in the country, and if a comparatively small shipyard finds it desirable to manufacture its own supply, how much more advantageous will it prove to the Navy Department.