Following on the paper I read before this institution last year upon Naval Construction during the war, in which I gave a brief account of all the principal vessels designed and constructed during the war period, I now propose to give account of H.M.S. Hood, which will complete the series of big ships designed and built for the navy down to the present time.
Apart from the smaller craft, such as destroyers and patrol boats, of which an immense number were required during the war, the type of large vessel in which we were somewhat deficient in 1915 was the battle cruiser. It was known that the Germans were building several very important ships of this type, including the Derfflinger, Lützow, Hindenburg, and others to follow. Our own vessels were later to be supplemented by the Renown and Repulse, and there were the ver large light cruisers Courageous, Glorious and Furious, but these three latter could bot be regarded as battle cruisers in the proper sense of the term. __
*Paper read at the spring meeting of the 61st session of the Institute of Naval Architects, March 24.
TABLE.-Leading particulars of H.M.S. "Hood."
Length between perpendiculars
Load draught (L.W.L.), mean
Displacement at load draught
Shaft horsepower of engines
Speed at low draught
Oil fuel at load draught
Oil fuel capacity
Bulkheads, forward and aft
Vertical plating, magazines, etc
Forecastle deck, amidships
Upper deck, amidships
Lower deck forward
Lower deck aft
Weights expressed as percentages of displacement at load draught:-
Armor and protection
28 ft, 6 in.
8 15-in. B.L.
12 5.5-in. B.L.
4 4-in. H.A.
2 21-in. T.T. submerged.
2 double 21-in. T.T. above water
12 in., 7 in., 5 in.
6 in., 5 in.
5 in., 4 in.
15 in., 11 in.
11 in., 9 in.
1 in. | 1½ in. flat | increased to 3 in. over magazines
2 in. slope
1 in., 1½ in.
1 in., 3 in.
†The plating of the decks and side is required to be of such thickness for strength that it contributes very materially to protection. The weight of this plating is, however, included in "Hull."
I therefore received instructions in 1915 to prepare designs of battle cruisers embodying the latest ideas in regard to underwater protection, speed, etc. A considerable number of designs were submitted to the Board, but as there were no large berths available, it was not possible to place an order before the spring of 1916, and in March of that year the board selected a design of the dimensions given here to be worked out in detail and proceeded with. This design formed the original basis for the design of the Hood, having the same length and breadth as the Hood, but of considerably less draught, viz., 25 feet 6 inches normal and 20 feet deep, with a displacement of 36,300 tons on a length of 810 feet between perpendiculars. The speed was to be 30 knots, with machinery of 144,000 s.h.p. The armor, which was approximately equivalent to that of Tiger, consisted of an 8-inch belt and 9-inch barbettes. The armament was to be eight 15-inch guns and sixteen 5½-inch guns, together with two 21-inch submerged torpedo tubes.
I strongly advocated the adoption in this design of small-tube boilers, and these were accordingly included for the first time in the design of a capital ship. This feature had the most marked influence on the whole design, on account both of the smaller space occupied and the reduced weight involved, as compared with the space and weight which would be necessary for the large-tube boilers which had hitherto been adopted in all our big ships, including Renown and Repulse. The first big ships, though they cannot be regarded as capital ships, as mentioned above, which had the small-tube boilers were the Courageous, Glorious and Furious.
The original design of Hood was approved by the board in April, 1916 and orders were placed to build one ship each with John Brown & Co. Limited, Cammell Laird & Co., Limited, and the Fairfield Shipbuilding & Engineering Company, Limited, the ships being named, respectively, Hood, Howe, and Rodney. Subsequently an order for a fourth ship, H.M.S. Anson, was placed with Sir W. G. Armstrong, Whitworth & Co., Limited.
INFLUENCE OF THE BATTLE OF JUTLAND
It will be remembered that the Battle of Jutland took place on May 31, 1916. This, the greatest fleet engagement of modern times, naturally led to further consideration of the design of the Hood, which had only just been ordered; and, in view of the damage which was done to our own battle cruisers and also to the German ships of similar type, it was deemed advisable to increase the armor protection, if possible. As the result of very extensive investigations, it was found possible, by accepting a deeper draught and a slightly reduced speed, to add very considerably to the protection of the vessels as already designed, without serious modification to the design of the ship as a whole. Accordingly. in September, 1916, definite proposals for increased protection were submitted. The alterations were of a very radical character, the armor belt being increased from 8 inches to 12 inches, and the barbettes from 9 inches to 12 inches; and certain increases were also made in the deck protection. The particulars, as thus finally decided, are given in the table. At the same time the eight 15-inch gun mountings had their design modified to admit of anelevation of 30 degrees, and certain other modifications were made, both in the torpedo armament and also in the arrangements, for preventing the flash penetrating to the magazines--a form of protection which was elaborated for all our ships at this time. All these increases involved an additional weight of nearly 5,000 tons, the legend displacement of the Hood becoming finally 41,200 tons when carrying 1,200 tons of fuel; the ship then having a draught of 28½ feet, and a draught of 31½, feet with full fuel load, viz., 4,000 tons.
The original length and beam of the ship were maintained as before. Some extra plating had to be provided on the decks for strength purposes, but the underwater protection against torpedoes, which had proved very efficient, was retained, as in the original design.
I should mention also that the stability conditions were such that the increased displacement could be accepted whilst still maintaining a very satisfactory metacentric height.
DESIGN FINALLY APPROVED IN 1917
All the modifications made in the design after the Battle of Jutland were considered in consultation, not only with the Board of Admiralty, but with the Commander-in-Chief, involving, as they did, special arrangements for the fire and torpedo control, arrangements of bridges, etc.; and it was not till 1917 that the design was finally approved in all its details. This change naturally militated against the quick construction of the ship, and it will be about four years from the approval of the original design, in April, 1916 to the time of her completion, this being about double the time taken to build our recent capital ships, and nearly three times that taken to build H.M.S. Repulse and Renown. It is only fair, however, to say that the modifications were quite justified by the circumstances, and they have no doubt made the ship a much more powerfully-protected one, whilst increasing her displacement, and consequently the weight of material to be worked, to about 50 per cent more than that of Repulse and Renown.
The main machinery, consisting of geared turbines to develop 144,000 horsepower, is the largest power which has ever been put through gearing, namely, 36,000 horsepower on each of the four shafts. The machinery is placed in three engine-rooms, of which the forward one contains two independent sets for the outer shafts: the middle and after engine-rooms containing one independent set for each of the inner shafts. This power, which was designed to give 32 knots for the earlier design of 36,300 tons displacement, is expected to give at least 31 knots in deep water at a displacement of 41,200 tons for the Hood as built.
The revolutions per minute of the propellers are 210 at full speed, and this admits of the adoption of propellers of higher efficiency than many we have had in our capital ships before gearing was introduced, when the revolutions were considerably higher.
The boilers, 24 in number, as mentioned above, are of the small-tube type with forced draught, and are arranged in four boiler-rooms. I t was known that a great number of the later German capital ships took advantage of the reduced weight and space occupied by small-tube boilers, and have generally adopted them in their recent designs. It is hardly necessary to say that oil is the only fuel used in Hood.
It will be seen from the plate drawing that the main armament of eight 15-inch guns is mounted, as in our recent battleships of the Queen Elizabeth and Royal Sovereign classes, in four turrets, all on the center line. The heights of the axes of the guns above the normal load waterline for each turret, commencing from forward, are 32 feet, 42 feet, 31 feet 9 inches and 21 feet 9 inches. The big guns have very large arcs of training, the forward ones training to 60 degrees abaft the beam, and the after ones to 60 degrees before the beam.
The anti-torpedo boat destroyer armament consists of twelve 5½-inch guns with shields 1 inch thick, these guns being arranged on the forecastle deck and shelter deck as shown. There are also four 4-inch antiaircraft guns on the shelter deck aft.
There are two 21-inch submerged torpedo tubes, each in a separate compartment forward, and four 21-inch above-water torpedo tubes between the upper and forecastle decks, these above-water tubes being a further addition since the original design was made.
The distribution of armor is shown on the plate drawing. The 12-inch belt has a length of 662 feet and a depth of 9 feet 6 inches. Above the main belt is a strake of 7-inch armor to the height of the upper deck, and above that again there is 5-inch armor between the upper and forecastle decks. The side armor all slopes-outward from below, as seen on the section, so that the virtual thicknesses are really somewhat greater, as the shell cannot thus hit the armor normally. There is thick plating behind all the armor, varying from 2 inches over the greater portion to 1½ inches and 1 inch elsewhere.
The gun-shields for the turrets are of improved shape, with rather flatter roof than formerly, and the armor has a thickness of 15 inches in front, 12 inches and 11 inches on the side, with a thick roof plate. The conning tower arrangements have been very specially considered, and arrangements made, in addition to the Admiral's conning-tower, for torpedo and 15-inch gun control towers, and 5½-inch gun-control, revolving hood with range-finder, in addition to the range-finders provided in each turret. There are also smaller range-finders in connection with the different controls.
The torpedo protection consists of the bulge arrangement, with an outer compartment of air and an inner one specially strengthened with the necessary separating bulkheads, etc. This protection extends throughout the whole length of the machinery spaces and magazines, and it can be said that it renders the ship as sate against attack from torpedoes under water as she is against gun attack above water.
The oil-fuel tanks are arranged along the sides, thus giving additional protection.
It is a somewhat curious coincidence that the first series of recent experiments on under-water protection should have begun by a set of trials of torpedo charges against the old Hood, of the old Royal Sovereign class, built in 1893. Developing the lessons learnt from these trials, which took place in the years immediately preceding the war, the bulge protection was first designed and tatted at the commencement of the war in the old cruisers of the Edgar type, to which I alluded in my last year's paper. A series of experiments were then made at the request of the Admiralty by the late Professor (afterwards Colonel ) Bertram Hopkinson, F.R.S., in conjunction with myself, at first under the auspices of the Royal Society. These experiments, which were made on different scales gradually working up to the full size, were of the greatest value. and the original protection fitted to the Edqar was modified and the details of construction as modified have been largely adopted in the Hood. I am glad to have this opportunity of paying special tribute to the work of Professor Hopkinson and to his memory.
THE VALUE OF THE TORPEDO "BULGE." It may be noted that no ship provided with the original or the later form of bulge was lost, nor even seriously damaged by torpedo attack during the war, nor was there loss of life in any case; this being chiefly due to the special form of bulge and to its being external to the ship proper. By careful attention to the form the reduction in speed is only that due to the added displacement, amounting in the Hood to only a fraction of a knot.
Experience and trials have shown that the Hood, as protected, can receive the blows of several torpedoes and still remain in the line without serious loss of speed.
DOCKING QUESTION. In the design of the Hood special consideration had to be given to docking and she is provided with double internal vertical keels along the center line, and the docking keels come under the longitudinal bulkheads to support the ship on each side. Arrangements are made to dock the Hood in our larger docks, and she has already been docked and prepared for trials at H.M. Dockyard, Rosyth.
I should like to add that it was never proposed to dock the Hood at Devonport, although one of the technical papers stated recently that it was discovered that she could not be docked there. Whenever a design is got out at the Admiralty, or presumably anywhere else, when fixing the dimensions, one of the first points to consider is, where the ship is to be docked; and this was done for the Hood, both in the case of the original design and again later when the protection and displacement were increased.
The Hood was successfully launched in August, 1918, at Clydebank, the ceremony being performed by Lady Hood, widow of Admiral Hood, who lost his life whilst gallantly leading into action the Third Battle Cruiser Squadron at Jutland.
LAUNCHING WEIGHT, 22,000 TONS
The launching weight was about 22,000 tons. As the other three ships of the class which were commenced had none of them reached the launching stage at the time of the Armistice, it was subsequently decided not to proceed with them, in view of the international conditions, and the Howe, Rodney and Anson were accordingly scrapped.
The general strength of the ship as a girder had to be thoroughly investigated, both the original design and again when the protection and displacement were increased. Assuming the ship among waves equal to her length from crest to crest and one-twentieth of that length in height (a condition which I do not think is ever likely to be met with), the maximum tensile stress on the top of the girder is less than 10 tons per square inch, and I may add that not one of our recent ships has ever exceeded this amount, although a slightly greater stress has been accepted in some recently designed Atlantic liners. The maximum tensile stress on the keel is less than the above, and the maximum compressive stress does not exceed 9 tons per square inch.
The following are some particulars of the general outfit:
Dynamos-- Eight dynamos are provided and are widely separated, two are driven by Diesel engines, two by turbo engines, and four by reciprocating engines.
Hydraulic pumping engines-- Four hydraulic pumping engines are provided for working the turrets; these and the other more important auxiliary engines are kept well away from the ship's side, as are also the necessary feed tanks.
Pumping and flooding arrangements-- Special consideration has been given to this item in the design of the ship, electrical bilge pumps have been provided. and also some 100-ton submersible pumps to deal with any water that may enter the ship. For fire and wash deck purposes a fire main is run all fore and aft under protection with rising mains at intervals. This fire main is charged from the 50-ton electrical pumps, and also from the 75-ton steam-driven fire and bilge pumps in the engine and boiler rooms.
In the boiler-rooms 1,000-ton turbo pumps are fitted; in each engine room the circulating pumps are arranged to draw from the bilges instead of from the sea, it required. Steam ejectors, each of 300 tons' capacity, are provided in the auxiliary machinery compartments and submerged torpedo rooms.
Steering gear,--The steering gear is of the right and left-hand screw type, with connecting rods attached to a crosshead on the rudder-head. Two steering engines are placed in the after engine-room with shafting led through the shaft passages and thence aft to the steering gear. Auxiliary steering on the Williams-Janney principle worked by electric motor is placed in the after-steering compartment. The main telemotor system is continued aft, so that this gear can be worked from the main steering positions of the ship. The following steering positions are provided: Conning tower, lower conning tower. after engine-room, steering compartment (auxiliary only).
Steering by hand power is not provided, as it has proved to be of little value with these very big, high-speed ships.
Capstan gear.--The anchors, three in number, each weigh 9½ tons, and the chain cable is of 3 3/8 inches diameter. Two cable-holders and a middle line capstan are provided, all connected to the capstan engine. A third cable-holder is provided for the sheet cable for letting go only. At the stern a 3-ton anchor is provided, and the after capstan is worked by Williams-Janney gear driven by an electric motor.
Special attention has been paid in our more recent ships, and perhaps more than any in H.M.S. Hood, to the system of ventilation, which has been worked out on the latest and most scientific principles; a great deal of experimental and research work having been done to get the best results. The main points to be noted are as follows:
The engine-rooms are ventilated by four 30-inch and three 40-inch supply fans, and four 35-inch and two 50-inch exhaust fans, electrically driven. Each of the auxiliary machinery compartments has two 17½-inch electrically-driven exhaust opens with "natural" supply trunks. all openings being well above the weather decks, in order that ventilation may go on as usual, even in bad weather--a very important point for the comfort and health of the crew. A very complete system of ventilation has been supplied to the seamen's heads, and to all w.c.'s, pantries, sculleries, paint stores, wash places, etc., the ventilation being generally by means of exhaust fans leading direct to the open air. The living spaces generally are ventilated by trunks supplied by electrically-driven fans. These trunks have openings so arranged that the air is delivered at a low velocity, and strong draughts which might be objected to are thus avoided and a gradual supply of fresh air, keeping the whole place sweet, is thus ensured. Where necessary, the air is passed through steam-heaters for purposes of warming. In all these arrangements care has been taken to maintain as far as possible the transverse watertight subdivision of the ship, by avoiding the piercing of watertight bulkheads. Each of the main transverse compartments is accordingly ventilated independently of any of the other main compartments, and thus the risk of water finding its way from one compartment to another in case of damage is eliminated.
Accomodation.--In all our recent designs great attention has been paid generally to the accommodation and comfort of the officers and men. Just before the war a special committee was appointed to inquire into the accommodations of ships, and a report was presented, and all recommendations of this committee have, as far as possible, been embodied in our recent ships. The exigencies of the war and the additional requirements which had to be met as the war progressed, to some extent prevented all the recommendations of the committee being carried out; but in the Hood practically the whole of these have been embodied and great improvements have thus been made, recreation rooms being provided, and greater facilities for cooking and similar operations. In fact, a modern ship is, in many respects, a home of luxury compared to ships even ten or fifteen years old.
Electrically-driven boat hoists.--Boat hoists, tatted with variable speed control gear of the Williams-Janney type, driven by electric motors, are provided, and a weight of 16 tons, that of the heaviest boat, can be lifted and lowered at a rate of 60 feet per minute.
As regards the general design of the ship, the Hood may be cited as an example of what can be achieved by going to a large size. The endeavor has been in her design to embody the armament and armor protection of a first-class battleship including also good under-water protection against torpedoes, and at the same time to give her the speed of the fastest battle cruisers. It has only been possible to do this by going to a great length and displacement. The under-water bulge protection is additional to anything provided in our pre-war dreadnoughts, although these ships had internal bulkheads. The addition of the bulge, which has entirely superseded the provision of torpedo netting. involved a considerably increased weight over and above that of a ship of ordinary form; and although this additional weight was accompanied by a somewhat greater amount of additional buoyancy. it still involved an increased displacement with the accompanying increase in resistance to propulsion.
It may be argued that. in such a large ship, a great many eggs are placed in one basket, and that a very expensive one, but it would have been quite impossible to combine the speed, armament, and protection in a smaller unit.
In connection with the size of the Hood and general considerations of design, it is, I think, interesting to note that of recent capital vessels built, and taking the chief characteristics of two classes of about the same displacement. in Queen Elizabeth we had a well-armored ship of about 28,000 tons with eight 15-inch guns, and speed of 25 knots. In the Renown and Repulse, of slightly less displacement, viz., 27,000 tons, though of greater length. we had vessels with 7 knots more speed than the Queen Elizabeth but with only six 15-inch guns against eight, and approximately about half the armor protection provided in the Queen Elizabeth. In the Hood we are providing the same armament, viz., eight 15-inch guns, as in the Queen Elizabeth, armor protection fully equal to, and in fact rather heavier in the aggregate than that of the Queen Elizabeth, 6 knots more speed than the Queen Elizabeth, which makes the speed nearly equal to that of the Renown and the Repulse, and, in addition, a full bulge protection against torpedo attack.
AMERICAN BATTLE CRUISERS
It is of interest to note that the American battle cruisers, which were originally designed with very light armor protection, have recently been modified in the direction of additional protection, making them thus more like the Hood, and in the Annual Report of the Chief of the Bureau of Construction and Repair for the fiscal year 1919, he says: "On June 24, 1919, the General Board recommended that battle cruisers be built as a distinct type, but the designs be changed to provide materially greater protection against gunfire and under-water attack. the resulting increase in displacement and reduction of speed, probably less than 2 knots, being accepted." This was approved, and the new plans necessary were got out. It is, I think, satisfactory that the American authorities, who have had full knowledge of what we have been doing in this country in the design and construction of warships, should have thus come to the conclusion that we were on the right lines, and have modified their design accordingly.
As regards cost, which is about £6,000,000, this, of course, is an enormous sum, but when the displacement and size of the ship and her qualities are considered, I do not think it is very excessive, in view of the present increase in prices. Most things have doubled in cost, and many of our pre-war capital ships, complete with their armaments, etc., cost, on the average, about £90 a ton of displacement. The Hood is costing about £145 per ton, or an increase of only 60 per cent above pre-war prices, although she has qualities possessed by no earlier capital ship.
A good deal has been written and talked of lately about the surface capital ship being dead and the necessity for submersibles. But with our present knowledge it would be quite impossible to design a submersible ship which, on the same displacement and cost, had anything like the fighting qualities on the surface which are possessed by the Hood. Every ship is a compromise, and if in addition to the ordinary qualities of a battleship she is required to submerge, or even partially submerge, a very considerable percentage of weight has to be added to give her this additional capability of submergence. She becomes still more of a compromise, and the added weight must detract from the fighting qualities of the ship when on the surface, so that, whatever is done, other things being equal, the submersible ship must be inferior to a surface ship in an ordinary action. There are many difficulties of details in the design of a submersible battleship which would take too long to go into fully now, and although there is no doubt that submarines are capable of great development, a little thought will make it clear to anybody that if naval warfare is to continue, the surface ship of the line must still hold the field as the principal fighting unit of any great navy. This view is apparently shared by other countries who are developing their navies, and both Japan and the United States are building large capital surface ships.
I should like to take this opportunity on behalf of my staff and myself of thanking the contractors for the assistance they have given us in getting out working drawings of the Hood; this applies not only to John Brown & Co., who have so successfully constructed this. the largest shin ever built for H.M. Navy, also to the other three three who. in the earlier stages, helped us with the plans until the time came when it was decided not to proceed with the three ships ordered from them.
In addition to the printed paper, Sir Eustace d'Eyncourt said:- "Since my paper was printed, the Hood has been undergoing a very exhaustive series of trials which are not, however, yet completed, nor have the results of the trials which have already taken place yet been thoroughly analyzed.
"However, the speed trials at normal draught were completed last week and very excellent results obtained.
"On the full power trial, at a displacement of 42,200 tons, which is considerably in excess of the normal load draught, a speed of 32.07 knots was obtained, as a mean of runs taken on the measured-mile course off the Isle of Arran in deep water. This was obtained with a mean horsepower of somewhat over 150,000 and with 206 mean revolutions of the propellers. The day was not altogether satisfactory, as there was a very high wind- about force 6.
"The engines worked very satisfactorily and a power of between 145,000 to 150,000 was maintained for a period of about seven hours. It is also interesting to note that or; the two-fifths power trial a mean speed of over 25 knots was obtained. The propulsive coefficient was in all cases satisfactory, varying from 53 to 55 per cent, and a very satisfactory fuel consumption was also obtained.
"The ship, therefore, with the 5,000 tons increased protection, now has the original speed of 32 knots, which was that laid down for the lighter ship of 36,000 tons. Her full speed, with full fuel and all weights and stores on board will be at least 31 knots with full power."-
" Shipbuilding and Shipping Record."