The alleged characteristics of the German battleship Ersatz Preussen have been published. There has been much comment in the press as to this wonder ship, which is to cause consternation in all the navies and is heralded as almost the work of magic. An examination of the alleged characteristics from a dispassionate technical angle fails to show anything magical about the vessel, but it does appear to indicate that the German Admiralty have permitted their engineers to produce, without undue technical or financial restrictions, what their engineering talent is able to, by utilizing materials, processes, and methods that are available to them. Somewhat similar results might be produced in other countries under like conditions.
The battery of six 11-inch guns and eight 6-inch guns is not inconsistent for a small battleship. By reducing the power to one-half that of the 10,000-ton light cruisers, 1,000 tons of weight have been saved that can be put into a heavier battery and increased armor. This battery does not weigh in excess of 50 per cent above that on our 10,000-ton cruisers.
The reports allege that the hull is entirely welded. This is more or less doubtful, but no doubt welding is used very extensively. This is entirely sound practice and can, also, be done in this country. By the substitution of welding in lieu of riveting, and welded structures in lieu of heavy castings, a saving of weight of eight hundred tons can readily be made in the hull and machinery of a 10,000-ton vessel.
There is nothing to prevent the U. S. Navy, or the English or French Navies, using welding as extensively as it has been used in this German vessel. United States’ welding technique is, I believe, fully up to that employed in Germany. United States’ industry is using it very extensively. All that stands in the way of using it much more than we have heretofore in naval construction is a certain excess of conservatism. However, we have some welded turbine casings already in service in our Navy and more are likely to come. We are on the eve of having welded boiler drums.
The Diesel engines are said to weigh only seventeen pounds per horse power. This is less than half the weight of the large Diesels being built for United States submarines. This weight, I take it, refers to the Diesel engines alone and not the total machinery weight. The total machinery weight would be about twice this, or thirty-four pounds per horse power, or about the same as our light cruiser machinery. This saving of weight has been secured probably by substituting aluminum and other lightweight alloys (possibly magnesium) for steel and iron. Our automobile engines and aircraft engines have been doing this for years. It is expensive, but in aircraft engines we have gotten below 1.5 pounds of engine weight per horse power. Diesel engines for aircraft weighing about three pounds per horse power are being built. If the engines are double-acting, weight would be saved by this expedient. It is also likely that the engine units consist of several cylinder groups connected to a shaft by reduction gear. This enables high-speed engines to be employed, tends to save weight, and provides for engines that can be placed below the protective deck.
Whether these Diesel engines will be as reliable as turbo-reduction gear remains to be seen. It is possible, but from past experience with Diesel engines, either German or otherwise, it is doubtful.
The power of the German ship is less than one-half that of the fast 10,000-ton cruisers. And, here again, is the question of whether the sacrifices made to secure the 35-knots or more speed are worthwhile. By reducing the power over 100 per cent with a speed of twenty-six knots, the German ship has considerable armor and heavier armament. This 10,000-ton battleship will cost more than double and possibly three times what a light cruiser would cost in Germany. Would the United States or British Navy rather have one Ersatz Preussen or two Pensacolas or Londons? That is another way of looking at it. The British and U. S. Navies have battle fleets of heavy capital ships. The Germany Navy does not. That is another factor.
Other navies could profit by following the example of the Germans in using welding more extensively, the use of light alloys and alloy steel where the expense is not too much, and the use of the light-weight Diesel as a cruising auxiliary engine; but, as long as they have their capital ships, some of which approximate the speed and endurance of this new prodigy and have vastly heavier guns, it is not likely that this type of vessel will be found in the building programs of the great navies. They can get more for their money in a cheaper design. Germany is restricted as to the size of the naval vessels she can build; the Ersatz Preussen is apparently the most powerful vessel that can be produced on the limited displacement, regardless of expense.
Cruising Radius and Reliability
For high-powered vessels, high-pressure steam and turbo-reduction gears, in which full advantage of use of light alloys and welding is taken, are likely to give a lighter weight of machinery than will Diesel engines. By going the limit on this matter, total machinery weights for a 100,000-horse power installation could be brought down to twenty or twenty-five pounds per horse power, together with a fuel consumption of about 0.6 pound of oil per horse power for all purposes. The corresponding figure for the Diesel would be about 0.45 pound, while the figure for our present light cruisers building would be 0.8 pound. We could be fairly well assured of the reliability of the steam machinery, while the reliability of the very light-weight Diesel would first have to be proved.
The steam plant could secure a very large cruising radius by installing Diesel-electric cruising equipment capable of driving the vessel very economically at about twelve to fifteen knots. This combination would secure a very great steaming radius at low speeds and reliability and reasonable cruising radius at high speeds. It is believed that this, all things considered, would be a better machinery installation for high-speed naval vessels than a full Diesel installation. The Diesel may give a greater radius at the higher speeds, but the lightweight Diesel machinery cannot as yet be regarded as being as reliable.
Use of High-Tensile Alloy Steel for Structure and Machinery
A limited amount of weight can be saved by the employment of higher strength steel; also, by special refinement in design, so that unnecessary metal is left off where it is not needed. In various places lower factors of safety may be employed without serious risk, provided the actual stresses to which the material is to be subjected are known. Perhaps, with all this refinement, a saving of 10 per cent of the metal weight could be secured. This, again, would represent five hundred to six hundred tons, and would mean considerable increase in cost. Special protection from corrosion, also, might enable metal parts to be lighter, since less allowance for corrosion would have to be made.
If the technical designer were unrestricted as to what he might or might not do, he could produce a very material saving in weight, as well as secure substantial reduction in fuel consumption. For various reasons, restrictions are placed upon his decisions and judgments; some of these are often unsound and unjustified. Compromises have to be made to satisfy various requirements. Again, the ship is required to do too many things that interfere one with the other. It is not quite possible to have a greyhound and a bulldog in one unit. It is much more satisfactory to secure two dogs, one of each breed. The upshot of these various compromises and restrictions is that almost any vessel as built does not represent the maximum of what our technical forces can produce.
There is always the danger of trying to have a design do too much. This has accounted for many abject failures in nearly all navies. A ship is limited by her displacement. This cannot be stretched or twisted into anything else. Usually the most satisfactory designs are those that do not attempt to work magic and allow satisfactory weight and space for everything essential and leave off as many non-essentials as possible.
The Ersatz Preussen will be a very interesting engineering experiment and her actual operation will no doubt serve to teach many lessons. There appears to be no compelling reason for the large navies to rush in and build vessels of her particular characteristics. However, many of the technical methods that she employs can be taken advantage of.
New Light Metals Used
From some information coming from Germany, it appears probable that both silumen and electron metals are being used largely in connection with the light-weight Diesel engines.
Silumen is an alloy of aluminum, with about 11 per cent silicon and 5 per cent iron. It is a strength metal with better ductility than other aluminum casting alloys and relatively greater strength, and is primarily a casting metal. It does not appear to be any stronger than alloy used in this country and in England. Alloys similar to this are in this country for various special purposes.
Electron metal is a special magnesium alloy, about 90 per cent magnesium, somewhat stronger and lighter than aluminum alloys. It appears to be produced with varying amounts of zinc and aluminum, and sometimes copper. Magnesium alloys have been tried in the United States, but without very satisfactory results, owing to the instability of the material. When tried for pistons of aviation engines it has not shown satisfactory service, and, owing to its tendency to disintegrate, particularly in the presence of moisture and salt water, it is necessary to have some thoroughly effective coating before it can be used with certainty. No doubt some improved means of making this metal more suitable to withstand these conditions have been developed recently, and may be in use on the Ersatz Preussen, but until the effectiveness of these measures has been fully demonstrated in service, there is an element of doubt about its lasting qualities. Electron metal would be used largely for castings, but is also supplied rolled and in sheets. It is understood that zinc coatings are sometimes used in protecting it from effect of salt water or other corroding media.
The use of these new alloys shows progressive engineering and enterprise; whether it is rash can only be determined from actual experience.