Home - Dits & Bits - BR3043 - Part Two - Progressive Development of Design and Equipment - Chapter 25

Chapter 25: Main Engines and Fuel Arrangements

25. 1 Main Engines

1. The Holland boats were fitted with a horizontal 4-stroke Wolseley gasoline engine with four cylinders, each cylinder single-acting and balanced to prevent excessive vibration. The cylinders, of cast iron, were fitted in pairs each pair surround­ed by a water cooling jacket, water being circulated by the main bilge pump from the main line. Later on a small single-acting plunger type pump geared from the main shaft with suction direct from the sea was fitted for circulating engine cooling water. There was no piston cooling. The designed full power was 160 bhp at 320 rev/min and a state­ment has been seen that the horse-power could be increased to 190 bhp by increasing the revolutions to 390. Whether this was ever done in practice is doubtful. The engine was started by the main motor and was non-reversible. Therefore the submarine could go astern only on the main motor.

A detailed account of this engine which was the type used in the USN Holland boats of the AdderClass is given in Commander Sueter's book together with an interesting account of other types of engines being used in submarine boats at this period.

2. Reference (3) states that the consumption of the Holland -Otto type 160hp engine varied between 10 and 12 gallons per hour. This was probably from an American source. When quoting from the specifications for Holland No 10 (the Adder Class) the same reference gives a consumption of 1 pint of gasoline perhp hour, equivalent to 20 gallons for 160 bhp. This is undoubtedly nearer the true figure. Vickers test figure for consumption was 0. 875lb per bhp hour which is equivalent to about 20 gallons per hour at sg of about 0. 71. Six hundred gallons of gasoline were carried in one tank right forward under the torpedo tube.

3. Both the engine and the main motor were geared to the 4in diameter propeller shaft, gearing being provided as follows:

  • Main engine to propeller shaft, gearing 1:1. 9.
  • Main engine to main motor for charging batteries,
  • Main motor to propeller shaft.
  • Main motor to main engine for starting engine.

An air compressor was also geared from the main engine for charging thehp air bottles and the main bilge pump was operated through the same gearing.

The gearing enabled the engine to be well down in the vessel at a much lower level than the shaft which was on the axis of the boat. This of course was an essential require­ment to enable the engine to be fitted in the boat at all.

The exhaust from each cylinder was led outboard to a single gasoline exhaust box on top of the pressure hull. The arrangement is shown in Plate 1.

4. Air supply to the engine room was natural through the conning tower as it was to the remainder of the boat and also through one 10in ventilator fitted over the fore end of the engine room with a butterfly-clipped cover on the inboard side of the ventilator. There were no exhaust fans in the boat except for battery ventilation.

5. It was early realised that the ventilation was inadequate and would have to be improved because of the danger from gasoline fumes. To do this exhaust fans were fitted abaft the engine room partial bulkhead with one above the gasoline engine and another just forward of it both ventilating into the 10in ventilator. In spite of this an explosion occurred in Holland No 2 in March 1903 whilst proceeding up Portsmouth Harbour after manoeuvres. Free gasoline from a leaky joint formed an explosion mixture in the after end of the boat and exploded when an electric switch was made to start up the motor. Several of the crew were badly burned. It is interesting to note that when the question of gasoline leaking from the fuel system was discussed in 1905 the Inspecting Captain of Submarines stated 'that every petrol joint in the boat is made to withstand a pressure of 2000lb/in2 whilst its working pressure is only 1lb/in2 and there ought to be no leaks'

Speaking further on this subject Captain Bacon goes on to say, after mentioning an explosion in A5 caused by leaks from a badly packed gland in the petrol pump»that 'the smell of petrol inside a boat is almost unknown. Boats are particularly free from all chance of accident with the engines running since the volume of air used every two minutes is equivalent in volume to that of the whole air in the boat. The tanks are constructed so that leakage is impossible (he is presumably meaning the water jackets round fuel tanks introduced in A Class onwards). English boats have covered over 30000 miles under their engines and with the exception of one small flash in an early boat (presumably Holland No 2 mentioned above) no explosion except that in A5 has occurred'.

6. Details of the Wolseley engine fitted in the Hollands and A Class are given in Appendix VIA and of all the engines built by Vickers up to the L Class. Other classes are given in Appendix VIE.

7. In A1-12 a similar type Wolseley engine was fitted. Vickers state that they all had sixteen cylinders with a designed bhp of 600 although they give no power for A1 whilst Sueter gives 'the engines of the A type were made chiefly by the Wolseley Co and have twelve cylinders which develop about 600 bhp'. An A2 inclining experiment mentions a twelve cylinder engine. There are definite differences in the size of the engines fitted in A1, A2-4 and A5-12 and the powers were also different without any doubt. There were changes in diameter of cylinder, piston stroke, weight and size between A1, A2-4 and A5 onwards presumably due to development by Wolseley. From all the evidence the conclusion is that the engines in all boats of the class had sixteen cylinders (Plate 2 : of A1 shows sixteen cylinders) and that the power in A1 was 350 bhp, in A2-4 was 450 bhp and in A5-12 reached 600 bhp. The revolutions at full power were 400 rev/min. In A5-12 the engine could be started by air as well as by the motor.

8. In A1-4 the exhaust pipes from the eight port cylinders passed individually through the hull into a main exhaust pipe outboard below the WL. Similar arrangements were fitted for the eight starboard cylinders. The two main exhaust pipes ran aft to abreast the after end of the engine and then combined into a large vertical U-bend on top of the hull before passing into a muffle box fitted with a closure operated from inboard.

When on the surface the U-bend was an outstanding projection well above the waterline.

9. The dangers consistent with using petrol in a boat which was frequently closed up with little or no ventilation necessitated stringent regulations to prevent accidents and great precautions to prevent leakage. The explosion in A5 at Queenstown at the beginning of 1905 was a case in point. A leaking gasoline pump allowed free gasoline in some quantity into the boat and it vaporised quickly. To clear the boat of fumes the main motor was started to turn the engine to suck foul air from the boat. The explosion was caused by sparks from the main motor brushes. The adoption of diesel engines using heavy oil with a higher flash point was an obvious move. About the time the B Class was being designed trials were being carried out on diesel engines by Vickers and they were sufficiently promising for A13 to be fitted with a diesel so that exhaustive trials could be done at sea. These experiments were begun in 1903 and the first engine built by Hornsby-Ackroyd was not a success. The ultimate success of the experiments carried out by Vickers 'largely depended on the company's patent system of fuel injection'.

10. The engine in A13 was a Hornsby-Ackroyd six cylinder vertical heavy oil engine of 500 bhp at 380 rev/min. It was about 3. 0 tons heavier than the 600 bhp petrol engine in A5-12 and in consequence this increase in weight had to be compensated by removing the after fuel tank and its structure fitted in the earlier boats. In any case the tanks under the engine had to be removed because of the increased height of engine and lower shaft line which had to be angled upwards to the propeller. The amount of fuel carried was in consequence only 3. 7 tons and the endurance suffered although figures of fuel consumption in lb per bhp hour given by Vickers were much better at 0. 42 as against nearly 0. 9in A5-12. On passage from Barrow to Portsmouth the diesel ran for 29| hours with four cylinders in use at an average of 200 rev/min and 20 gallons per hour consumption, undoubtedly an extremely good performance at the time. Although heavier this engine was shorter and much narrower than its equivalent powered gasoline engine but the overall height was nearly double.

The exhaust from the engine passed outboard through an exhaust valve overhead just aft of the engine. The exhaust pipe then ran forward inside the casing to the after side of the conning tower where it rose in a U-bend over 3ft high and then ran right aft on top of the hull to the muffle box. This represented nearly 70ft of large exhaust piping outside the hull. Variations in this principle were used in the arrangements adopted in the B Class and C Class, the main difference being in where the exhaust pipes passed from the engine through the pressure hull, as shown in Plate 5, Plate 6, Plate 7 & Plate 8. These were the original arrangements and some modifications may have been made after experience with them.

11. The B Class and C Class were fitted with the same sixteen cylinder Wolseley gasoline engine as in A5-12 but now made by Vickers and called the Vickers engine, developing 600 bhp at 400 rev/min except that in C19 onwards the number of cylinders was decreased to twelve. They however developed the same power of 600 bhp. Although the diameter of cylinders, stroke, revolutions, etc were the same there was a reduction in weight in lb per bhp from 62, 7 to 59. 5 and a cut in the overall length of 4ft. The air starting of the engine in A5-12 was deleted in both classes.

12. Although no seagoing experience had been obtained with the engine in A13, diesels were adopted for the D Class and so saw the end of gasoline engines in new designs. On service the gasoline engines did give a certain amount of trouble; other nations were experiencing even more trouble than we did.

The D Class were the first twin engined RN submarines. They had two vertical single-acting six cylinder diesels each developing 600 bhp at 380 rev/min. They were 4-stroke engines and fitted for blast injection. The diesels were heavier than the petrol engines of the C Class with the same power, the weight in lb per bhp rising from 59. 5in the last C Class to 69. 0in D1, 72. 7in D2 and 73. 0in D3-8. The length of the engine increased by nearly 2ft and the height more than doubled. The outstanding advantages were improved reliability and safety and a better fuel consumption. The engines could be started by air as well as by the motors a practice started in A5-12 but dropped for the B Class and C Class. They were fitted with their own engine air compressors having a capacity of 297. 5ft4per minute at 1200lb/in2 discharge pressure.

The exhaust from each engine was led outboard to a U-bend in the superstructure and then inboard again to a drowned exhaust in the after end of the externals Port and Stbd sides.

13. For the E Class the D Class engine was adopted but with the number of cylinders increased to eight, giving 800 bhp at 380 rev/min, a total of 1600 bhp. The additional two cylinders per side meant an increase in length of each engine of approximately 3ft and a total increase in weight of about 7-8 tons. However, the weight in lb per bhp decreased from 73. 0in D3-8 to 65. 3in E1 and was below 64. 0in later vessels of the class. Furthermore the fuel consumption in lb per bhp hour fell from 0. 54 in D3-8 to 0. 47 in E1 and to 0. 455 in E19-24. In general more room was given for the engines and motors than in previous classes.

At the outbreak of War in 1914 when thirty-eight E boats were ordered under the Emergency War Programme all to be fitted with Vickers engines, Vickers had to grant licenses to about twenty firms of oil engine builders to meet the demand.

14. The same design of engine had therefore been adopted for the D and the E Class except for the number of cylinders. D1 completed trials off Fort Blockhouse in 1910 after which improvements to the engines continued. Experiments with solid injection were carried out in D6 with the ultimate conversion of the remainder of the class and the E Class engines were built with solid injection. Solid injection continued to be fitted to all submarine diesel engines, except in S1-3, G14, and the H Class and R Class, until in the 1920's from X1 onwards the revertion to blast injection was made. Forced lubrication was fitted for the first time to the engines of D3.

So far all the engines had been 4-stroke but in E3 the experiment was made of fitting 2-stroke blast injection engines of Carel design from Belgium. This was unsuccessful due to overheating of pistons and liners. The engines were removed and replaced by two sets of Vickers standard engines. This would account for the delay in completion of E3 of about one year. The only other RN submarines fitted with 2-stroke engines were F2, S1-3 and G14. The G14 engine was not a success.

Cast iron cylinder jackets had been fitted in the Holland boats and continued to be fitted up to E16. From E17 onwards steel was used in place of cast iron and this became standard practice. Steel cylinder jackets were also fitted in the V Class and Nautilus which had been ordered one year ahead of El7 but the latter was the first boat to complete.

In the E Class the exhaust from each engine was led outboard to the fore end of an exhaust tank built as part of the superstructure. Pipes were led from the after end of the tank port and starboard sides round the hull to near the waterline. This marks the begin­ning of the engine exhaust tank.

15. The S Class was a Laurenti double-hull design developed by the Fiat San Giorgio Company of Spezia, Italy. The three boats of this class were fitted with two Scott-Fiat vertical 2-stroke diesels developing a total of 650 bhp at 460 rev/min. There is doubt whether 650 bhp was developed on service the more likely figure being 600 bhp.

16. The following details of the engine are quoted by Scotts:

'The Scott-Fiat diesel engine differed from that in use in previously built British submarines, being of the reversible two-cycle type capable of using any kind of fuel oil. The specification required that the specific gravity of the fuel oil should not be less than 0. 9 and that the engine should be able to start on fuel of not less than 0, 82 specific gravity and 150 F flash point without using compressed air, except for a few revolutions to get compression. In view of the novelty, we give a complete description.

The engines are of the six cylinder diesel marine type, each set capable of developing 325 brake horse-power at under 460 revolutions per minute, and on a weight of approximately seven tons without oil or circulating water. The engine is reversible, the operation of going from 'full ahead' to 'full astern' occupying less than ten seconds. It is of the two-cycle type, the scavenging air being provided by using the lower part of the stepped piston as an air pump. The air is drawn in and delivered through a piston valve operated by gearing from the vertical shaft which drives the cam-shaft. This scavenging air is admitted to the cylinder at the correct moment by mechanically operated scavenging valves in the cylinder head. The exhaust is by means of ports in the walls of the cylinder uncovered by the piston at the bottom of its stroke. The engine is started by compressed air, which may be admitted to three or six cylinders as required. The fuel is sprayed into the cylinder by compressed air and is delivered to the six fuel-injection valves by a single pump. The regulation of the fuel supply is obtained by a mechanism which keeps the fuel pump suction valves open for a longer or shorter period according to the amount of fuel required. The compressed air for spraying the fuel is supplied by an air compres­sor of the three-stage type, worked by a crank on the main engine crank-shaft. The cooling water is delivered by a horizontal reciprocating pump driven by a single crank which, in turn, is actuated by toothed gearing from the main engine crank-shaft. The lubricating oil is supplied by a wheel pump geared to the crank-shaft. All lubrication is forced and the cooling of the piston heads is provided for by the circulation of lubricating oil through a chamber in the piston heads. The cylinders are 9-3/8in, in diameter and 10½in. stroke; and the crank-shaft 5-5/8in. diameter'.

They were the first BN submarines with a main compartment allocated solely for the main engines.

17. The V Class was fitted with two Vickers eight cylinder diesels each giving 450 bhp at 450 rev/min. The engine in actual overall dimensions was very little different from that in the E Class of 800 bhp except that it was about 3ft shorter and the height above the centre line of crank shaft was 6in. less in the V Class than in the E Class engine. The latter was undoubtedly important since the maximum depth of hull amidships in the V Class was only 10ft 6in as against 15ft 0in in the E Class. There was however a saving in weight of 7-8 tons per engine although the weight in lb per bhprose from 6G. 5 in E14-16 ordered at the same time to 84. 0in V1 and 79. 0in V2-3. The diameter of cylinder and stroke was 10¾in and 13 in respectively in the V Class as against 14½in and 15in, in the E Class.

18. Nautilus had two Vickers twelve cylinder reversible diesels each of 1850 bhp at 340 rev/min. This was a bold jump in power per cylinder of over 50% from previous practice and also in the fact that the engine was made reversible. This was done at a cost in weight and space. The weight in lb per bhp rose to 78. 6 as against 66. 5in E9-11, the overall height rose to 10ft 8in as against 8ft 2in and the overall length to 41ft 2in as against 20ft 6in. The increases in dimensions were to be expected in doubling the power. The engine shop trials did not complete until 1916, Continuous trouble was given with liners and pistons and in 1917 the revolutions were limited to 300 rev/min.

19. The W Class was a French design with French engines of Schneider-Laubeuf design. They were of vertical 4-stroke solid injection reversible type. In W1-2 the two eight cylinder engines developed a total of 710 bhp at 400 rev/min. In W3-4 the engines were redesigned with six cylinders each and developed 760 bhp at 405 rev/min. There was a slight increase in weight in the latter but thehp per cylinder increased by over 42%.

20. The requirements of the F Class were engines designed to give a total of 900 bhp at 450 rev/min. This was the same as for the V Class. F1, the lead boat at Chatham, had two vertical 4-stroke solid injection engines of eight cylinders each, of 10¾in diameter and 13in stroke. It would appear that the engines were built by Chatham Dockyard. F3 was built at Thornycroft's and the engines for this boat were built by Vickers to the particulars given in Appendix VIA. F2 built by J S White had two six cylinder engines of the Nuremberg type improved by White's. They were of the 2-stroke type.

21. With Swordfish, a new phase in motive power for British submarines, appeared with the introduction of steam. The pros and cons of using steam for submarine propulsion as given at the time are to be found in Chapter 7. Swordfish was a Laurenti-Fiat design and was built by Scotts.

The Swordfish had twin screws driven by geared turbines of the Parsons type of a total horse-power of 4000 at shaft revolutions of 530 rev/min. An astern turbine was incorporated with each LP turbine. A Yarrow-type boiler of 4551ft total surface design­ed for a working pressure of 250lb/in supplied the steam through a superheater which raised the temperature by 100F. Further details are given in Chapter 7 Paragraphs 36 and 37.

22. The G Class was an exercise in trying to find a diesel engine other than the Vickers type for submarines. G1-5 were ordered from Chatham Dockyard to be fitted with Vickers engines of the E Class type i. e. two sets of 800 bhp each. Orders were also called for from outside firms, the type of engine being left to the builders. For G6-7 Armstrong Whitworth proposed to fit Nuremberg engines (MAN) in one and Sultzer engines in the other. Because of the war and other reasons Vickers type engines were subsequently fitted in these two boats. Vickers got G8-13 to be fitted with their own engines and Scotts, G14, to be powered by Fiat engines. Samuel White was given one boat to have their type MAN engine but this order was subsequently cancelled. Little change was therefore achieved.

Vickers standard E-type engines of 800 bhp each were therefore fitted in G1-12. The engines for G13 were similar except that they were reversible. Vickers made the engines for G8-13. It would appear that the engines for G1-7 were made by Chatham Dockyard and other firms. For G14 at Scotts that firm built and Installed engines of the vertical 2-stroke blast injection reversible type of Scotts-Fiat design each developing 800 bhp at 430 rev/min.

The reversible type engines in G13 and G14 were not successful and were eventually replaced by standard Vickers engines.

23. The J Class was a 'job in a hurry' to get a high speed overseas type submarine to sea. A well tried engine had to be adopted. The Vickers E Class engine of eight cylinders but increased to twelve cylinders so giving an output of 1200 bhp was chosen. Three such engines of 3600 bhp total at 380 rev/min were fitted, two in a forward engine room and one on the middle line in an after engine room, the motor room being sited between the engine rooms.

The characteristics of the engine were identical with the E boat engine except the length increased from 20ft 5½in to 29ft 6in. , a reasonable increase. The weight increased from 22. 3 tons per engine to 33. 6 tons which was in proportion to the increase in number of cylinders.

To provide for the 50% increase in torque and to eliminate alterations to shaft bearings etc the shafts were made of high tensile steel of the same diameter as the shafts in the E boats.

24. The K Class reverted to steam propulsion and this decision was taken before Swordfish had been to sea. Some details of the boiler room funnel and air intakes and the machinery are given in Chapter 8 Paragraphs 9 to 13.

Power was obtained from two sets of geared steam turbines which together developed 10500 shp, each set consisting of onehp and one LP turbine with an astern turbine incorporated in each LP turbine. Double helical reduction gearing gave shaft revs of 400 rev/min corresponding to turbine speed ofhp 3500 and LP 2800. The turbines in the Vicker's boats were of the Parsons type and in the others of Brown Curtis type. Steam was generated in two Yarrow type boilers working at a pressure of 235lb/in².

In addition an E Class eight cylinder diesel of 800 bhp was installed driving a 700hp dynamo. The purpose of this combination was:

  • To provide power primarily for the interval to raise steam after surfacing. The dynamo could supply current to the main motors for surface propulsion at about 9-10 knots.
  • For surface propulsion just before diving when shutting off steam.
  • Charging the batteries.
  • For a very considerable endurance at 9-10 knots and furthermore to reserve the turbines for the higher speeds.

25. The machinery and layout of machinery spaces was the same in K26 as in the earlier K Class i. e. 10500 shp although the machinery space was decreased overall by 3ft. Improvements in the design and height of the casings were made to give better protection to the funnels and boiler room air intakes and were very successful.

26. The L Class had two sets of the J Class engines of 1200 bhp each. a total of 2400 bhp at 380 rev/min. They were vertical single-acting 4-etroke trunk piston type with twelve cylinders of 14½in , bore and 15 in stroke. The design power per set was 1200 bhp at 380 rev/min and on tests are stated to have developed 1300 bhp at 400 rev/min. Vickers in their specification go further and give 1500 bhp at 450 rev/min. It is not therefore surprising that different figures for maximum bhp for this class are quoted.

Some details of these engines are that the cylinder liners were of special cast iron and the cylinder jackets of sheet steel. Oil pumps pumped fuel from the main tanks to ready use tanks situated above the level of the high pressure fuel oil pumps on the engines. Forced lubrication oil pumps, driven by the engines, were used for lubrication to both cylinders and the more important bearings. Two electrically driven turbine pumps supplied cooling water to the jackets and other parts where cooling was necessary. Air for starting the engines was taken from the shipshp storage bottles.

27. The M Class was powered with two sets of J Class engines with a total of 2400 bhp at 380 rev/min. Some authorities quoted 2600 bhp as developed on test. The L50L50 Class was similarly engined.

28. The engines in the Hl-20 Class were of American design, two in number vertical 4-stroke blast injection eight cylinder type with a total of 480 bhp at 375-380 rev/min. In the H21 Class the same type of engine was used. For the first boats engines were taken out of H10-20 building in the USA and shipped to England. It is interesting to note that although H21-32 were ordered in January/February 1917 the machinery and internal fittings for four boats had been delivered to Barrow by mid-May 1917. For the later boats the engines were made in England to the American design. One engine of this same type was fitted in the single screw R Class. With these two classes blast injection started again in lieu of solid injection.

29. X1 was fitted with a 4-stroke eight cylinder diesel on each shaft developing 3000 bhp at 390 rev/min making a total of 6000 bhp. The engines were of Admiralty design - a policy followed in later classes.

Two MAN auxiliary engines (ex the German Submarine U126) which were designed to develop 1200hp each, drove two generators which could drive the main motors in combina­tion with the main engines to give full power,

The combination of this machinery was:

  • The battery was charged by the generators.
  • The generators were driven by the auxiliary engines.
  • The main motors were driven by the generators (2000 hp) or the battery (2400 hp).
  • The propeller shafts were driven by the main engines and/or the main motors.

The design total power available for full surface speed was therefore 8000 bhp. It was found that the auxiliary engines did not develop 1200hp each side, their actual rating being about 940 bhp. This reduced the revolutions and the power of the main engines so that the totalhp available was taken as 7000 instead of 8000 as designed.

30. After successful full power trials in March 1926 and after a run to Gibraltar and back it was found that the teeth of the main engine vertical drive wheels were in such bad condition that they had to be replaced during the summer refit in 1926. During full power trials in January 1928 the starboard shaft fractured and a new set of gears was fitted, in April 1928 the port shaft fractured in the same place. The auxiliary engines andhp air compressors also gave trouble over the same period. The auxiliary engines in particular were never a success and needed continual refitting to keep them going. The main and auxiliary propelling machinery was the least satisfactory feature of X1 and she spent most of her life in Dockyard hands.

31. The Oberon Class was fitted with two sets of Admiralty design vertical 4-stroke blast injection six cylinders diesels giving a total of 2700 bhp at 400 rev/min in Oberon and 3000 bhp in Oxley and Otway at 400 rev/min. In the engines for the last two boats the cylinder diameter and stroke was increased to 19¾in as against 18in, in Oberon. DNC later gave these powers as 2950 bhp and 3170 bhp respectively. The latter obtained 3220 bhp on trials.

32. The Odin Class, Parthian Class and Rainbow Class had two sets of 4-stroke eight cylinder blast injection type diesels which were supposed to develop 4400; 4640 and 4640 bhp in the respective classes. DNC later give the bhp as 4520, 4340 and 4100 respectively. The design revolutions were 400 rev/min.

The Orpheus and the Parthian Class and R Class were fitted with Vulcan clutches. This clutch alone weighed in the Parthian Class 16. 8 tons and held 2. 6 tons of oil.

Some typical information about the main machinery for these classes is the arrangement in Perseus. The bhp of each engine was 2320 at 400 rev/min. The eight cylinders were 20 in diameter with 20 in stroke. Two Worthington-Simpson motor driven vertical centrifugal circulating pumps developed 90 tons per hour each. Two pumps for combined forced lubrication of main engine bearings and piston cooling made by Worthington-Simpson had an output each of 7000 gallons per hour at 60lb/in2. Two Worthington-Simpson pumps each with an output of 415 gallons per hour at 15lb/in2 were supplied for the Vulcan clutches. For starting the engines three air bottles of 8. 375ft4each at 1200lb/in2 were supplied and for blast injection two bottles of 3ft4each at 1200lb/in2.

33. Further details of the main engines in the Odin Class, Parthian Class and Rainbow Class are given in Chapter 14 Paragraph 54. The full power rating of all these classes was reduced to 90% in 1936 because of recurring piston seizures at the higher powers. All submarines had to do a full power trial every six months and Otus was the last to attempt it on the 25 May 1936 during which No 8 port piston seized. As a result the 90% restrictior officially came into being. This trouble may have been overcome later. As a point of interest Otway and Oxley had considerable trouble with their engines from the beginning mainly through 'wiped' top half of bearings. When Otway returned to Vickers for refit during the Second World War her blast injection engine was replaced by a solid injection type. This is the only reference seen to solid injection being adopted since blast injection became the policy in all Admiralty designed submarine engines.

34. Reference to the main engines in the Thames Class, Swordfish Class and Porpoise Class is made in Chapter 15, Chapter 16 & Chapter 17 and Appendix VIB.

25. 2 Fuel Consumption

35. The test bed figures for fuel consumption of the engines built by Vickers for the Holland Class to the J Class are given in Appendix VIA. The figures in Appendix VIB were given by RA(S).

The total fuel consumption figures for certain classes given by Vickers to cover all commitments as the boats left Barrow are as follows:

  Estimatedlb/bhp hour
Full speed Cruising speed
A Class . 885 . 95
B Class . 88 . 95
C1-18 . 715 . 80
C19-38 . 715 . 80
D Class . 518 . 60
E Class . 513 . 60

36. Some other fuel consumption figures available are:

  • (a) In the shop trials of the main engines for Osiris the figures were:
  Fuel Lub oil
72 hr 80% full power  Rev/Min   lb/bhp hour oz/bhp hour
Port engine 375. 5 . 394 . 22
Starboard engine 375. 2 . 394 . 176
8 hr full power
Port engine 401. 3 . 408 . 22
Starboard engine 401. 4 . 404 . 14
  • (b) In a two day trial in Otus in 1929 covering a speed range of 8 to 12 knots the lubricating oil consumption was 4. 5% of the fuel consumption.

25. 3 Oil Fuel Arrangements

37. Details of the quantity of fuel carried and the arrangement of tanks are given in the chapters dealing with individual classes.

38. The Holland boats carried 600 gallons (1. 9 tons) of gasoline in one tank under the torpedo tube forward. The tank was filled through a 1in connection on the hull near amidships with a lead to a 1¼ in cock on the tank top. The same line branched to a 1in cock on the tank top (presumably fitted with a tail pipe to the bottom of the tank) for 'engine gasoline return'-undoubtedly for discharging gasoline outboard. A ½in vent cock was fitted to the top of the tank with a lead outboard on the hull near amidships. Fuel was blown from the tank through a ¾in. 'gasoline engine suction' to a 'gasoline supply tank for carburettas' in the engine room by air (1in. pipe) at 50lb/in² reduced from thehp line. This seems to have been the general system adopted in all the gasoline carrying boats up to the C Class. Petrol depth indicators were fitted to the fuel tanks in C21 onwards and may have been fitted retrospectively in the earlier boats.

39. From A2 onwards the gasoline tanks were surrounded by water jackets except in way of the pressure hull as a precaution against gasoline leaking from the tanks into the boat. With riveted construction and petrol this was quite a possibility. The rules concerning the use of the jackets arc somewhat obscure, but it is certain that they were not always full of water when containing gasoline. In A2-12 the two jackets would contain 2. 0 tons of water; a very large additional weight to impose in these boats.

Each jacket was flooded direct from the sea through an 'inlet valve for surfacing water round gasoline tank' from which pipes led to the bottom of the forward and after cofferdams. From an 'outlet valve for surfacing water' a pipe was led to the top of the water jacket, A 1in pipe was taken from the 50lb/in² LP auxiliary air service to the jacket. It seems obvious therefore that the jacket was flooded direct from the sea through the inlet valve whilst venting through the outlet valve and blown by air in overboard through the inlet valve .

In most of the inclining experiments results seen with a full capacity of gasoline on board the water jackets have usually been empty but occasionally one has been full suggesting that the water was used for trimming purposes, and also occasionally carrying less than full capacity which suggests that there was some means of measuring the quantity of water in the jacket, e. g. by gauge glass or pet cock. It seems impossible that these early boats could, on the weight of water involved, have carried the jackets full when submerged. It is therefore assumed that the word 'surfacing', mentioned above in connection with the flooding valves, means that the jackets were empty when submerged and full on the surface when the fuel was being used i. e. under pressure.

40. In addition from A2 onwards individually named oil fuel compensating tanks appear.

In A13 carrying only 3. 7 tons of diesel oil neither water jackets nor special oil fuel compensating tanks were fitted.

41. Gasoline was replaced by heavy oil in the D Class onwards. Water jackets round tanks were deleted but with the increased fuel stowage for greater endurance the amount of oil fuel compensating water tankage also increased. In D1 there were eight such compensating tanks with a total capacity of over 17 tons.

42. In the E Class the problem of providing tanks to compensate for the oil fuel when used was greatly eased by the introduction of self-compensated fuel tanks. This idea was not new. C Richson, an engineer on the Naval Engineering Staff of the Swedish Navy had used this idea in 1902 in the Hajen-a design based on the Holland type. Reference (8) states 'in order to compensate for the loss of weight which ensued as the fuel (in this case paraffin) was used up, Richson introduced a method whereby the fuel expended was continuously replaced by sea water let in to the bottom of the fuel tank, causing the paraffin to float on top by reason of its lower specific gravity. This brilliant idea was subsequently taken up by other designers abroad'. This was eight years before being adopted in the E boats. The self compensation of paraffin in Hajenseems to have been quite satisfactory and this vessel ran until 1916 when she was reconstructed and her Avance-motor was then replaced by diesel engines. It is interesting that in 1908 the Swedes in their second class of submarines, which were about the size of the A Class, used benzine as fuel and this was also self-compensated. 'The driving machinery consisted of three equalised four-stroke internal combustion engines each connected to its own propeller shaft. The propeller of the midships engine had adjustable blades for reversing the direction of movement'.

43. The S Class was fitted with self-compensating tanks about this time and there was undoubtedly considerable development of the scheme going on by interested parties. Scotts give a few items of detail. They say that 'the two fuel tanks of the compensated oil fuel system were fitted with gauge glasses to show the height of the water level' and that the 'amount of compensating water in the tanks was measured by means of a water-meter, so that a very slight change of trim could be corrected with certainty between one dive and the next'. The same system was adopted in Swordfish 'in which there were forty-four oil fuel tanks. These were arranged in ten groups, five each side of the boat. An observation tank was fitted in the boiler room. It was a special feature that the compensating water valves and oil fuel suction valves were all situated in the boiler room. The earlier vessels of the K Class had no observation tank and depended on tank sounding apparatus. An observation tank as fitted in Swordfish was found by experience to be indispensable and was provided in the later K boats ; the control of the fuel was not centralised, however, as in Swordfish. ' A diagrammatic arrangement of the system in Swordfish is shown in Fig 25. 1 (not available).

An apparatus fitted in the K Class and subsequent classes for measuring the quantity of oil in any fuel tank, as claimed to be designed and patented by Scotts, is shown in Fig 25. 2 (not available). 'This consisted primarily of a tube in each fuel tank, so arranged that the oil level in the tube was made to correspond with that inside the tank. This being accomplished, means were provided for drawing off the contents of the tube into a special vessel in which the level of oil and water was clearly visible. By means of a scale the exact quantity of fuel in any tank of a group could be determined when required'.

44. With the pattern established for self-compensating fuel tanks even in the steam driven submarines, the fitting of special water tanks for compensating for the variations in weight in the oil fuel tanks as the oil was used gradually declined and the adjustment was made on auxiliary ballast tanks until the post war designs in the 1920's in which oil fuel compensating tanks (later called O compensating tanks) were fitted primarily for this purpose.

45. In the conventional submarines up to and including the E Class all oil fuel was carried in internal tanks inside the pressure hull. In the first double-hull type, the S Class, the fuel was carried in the external spaces between the two hulls. This practice continued in practically all the double-hull boats but the tanks in general were tested to a high enough pressure to count them as built to pressure hull standards. M2 was the first vessel in which oil fuel was carried in external tanks built to normal external tank standards of strength and actually tested to only 15lb/in², but they were in fact only for emergency oil fuel.

46. The L Class were the first boats to carry some of the normal fuel stowage in lightly constructed external tanks, although only two external tanks were used to carry a total of about 20 tons of fuel. This, however, started the practice which developed in the 1920 designs of carrying a large amount of oil fuel in the externals and trouble then started with leaks. In X1 and the Oberon Class, Odin Class, Parthian Class and Rainbow Class practically the whole of the fuel was carried in the externals. The tanks were riveted and tested to 20lb/in² and when submerged the pressure in the tanks was equalised to the external pressure. However, the tanks did leak at first to such an extent as to say they were a failure. In extenuation of the fact that the Oberon arrangement was repeated in the Odin Class and Parthian Class it must be stated that little service experience had been obtained in Oberon before the Parthian Class building was well advanced.

47. Oberon first reported oil fuel leaks in the middle of 1928 mainly from manhole covers. Even as late as January 1929 leaks in Oxley and Otway were thought to be due to bad equalising arrangements; in December 1927 Oxley had crushed in her oil fuel tanks whilst diving due to an equalising valve sticking. In July 1928 X1 reported leaks and RA(S) when questioned as to whether similar troubles had been experienced in Oberon replied that such leaks were due to defective rivets and that a further report would be made if experience showed that leaks were in part due to the plating, unfortunately no one realised the seriousness of the defects. At this time the Odin Class and Parthian Class were building and the Rainbow Class due to be ordered. Before designing the Odin Class it was pointed out that the external fuel tanks might leak on service. On the expenditure allowed the choice was between six submarines with external fuel or five with internal fuel and the former was chosen.

48. In September 1928 when submitting points for consideration in the new Rainbow design RA(S) stated that 'the position of the fuel tanks in Oberon Class, Odin Class and Parthian Class r enders them liable to leakage from expansion due to heat, shocks of depth charges or collision. Any leakage of fuel is objectionable as it indicates the submarine's position when submerged. It is considered that, if possible, as much fuel as possible should be carried inside the pressure hull and the fuel carried in external tanks should be as low as possible below the WL and in specially strengthened tanks'. No actual experience had yet been gained in the Oberon Class, Odin Class and Parthian Class. The financial position was still as acute as when the Odin Class were accepted with external fuel. However, the structure in way of the fuel tanks could be made stronger in the new design since the Odin Class had worked out light and there was weight to spare. In the Rainbow therefore the plating in way of the fuel tanks was increased from 14 to 20 Ib and the stiffeners increased accordingly. The oil fuel tanks were still placed above the main tanks because of the better flooding time of the latter and its advantage in diving. This arrangement also improved the stability submerged and in the low buoyancy condition.

49. The leaks on service in the Oberon Class, Odin Class and Parthian Class became extremely serious and even the extra thickness of plating and stiffeners in the R Class did not cure the leaking. Many attempts were made to overcome the defects including various types of packing in seams and laps. But they were all fruitless and the externals were ultimately successfully rebuilt in welded construction. In the Thames Class and Porpoise Class the tanks were welded as built and were very satisfactory except that in Thames whilst the external thin welded plates did not leak oil fuel did leak inboard in places through rivets in the thick pressure hull plating. In actual fact the trouble throughout had been caused by the rivets in an era when welded ship construction was in its infancy,

50. In the Swordfish Class a novel arrangement was tried of fitting a combination of self-compensated and non-compensated oil fuel tanks. The forward internal group of five tanks with a total of 17. 5 tons of oil fuel included one tank of 3. 0 tons which was non-compensated. The after group of three tanks of 22 tons of fuel included a similar non-compensated tank. As a result the amount of compensating water needed was less than 1 ton.

The Shark Class was designed with similar arrangements but in 1933 the non-compensated tanks were abolished as such. The arrangement had some merit but may have involved some difficulties in operation.