Home - Dits & Bits - BR3043 - Part Two - Chapter 20

Chapter 20: Hydroplanes

1. It was the fact that the Holland design of submarine had after hydroplanes only, which forced the boat to dive and change depth at an angle, which was responsible for the adoption of the Holland type by the USN in 1900. This method of diving was preferred by the American Navy to the horizontal dive using both forward and after hydroplanes advocated by other designers, especially Simon Lake in America. This is discussed in the opening paragraphs of Chapter 18.

2. In consequence the RN Holland boats had only one pair of hydroplanes, fitted aft and braced by arms from the stern plating as shown in Plate 1. They were made of double 10lb plates with an area each of 6. 5ft² and operated 60° from rise to dive. Whilst the boats were building, proposals were made that an additional set of hydroplanes should be fitted in the bows but this was not implemented because 'any interference with the plans of the Holland Boat Company might result in that Company disclaiming responsibility should any mishap occur'. It was also understood that 'no difficulty had occurred with the diving or maintaining a given depth within a variation of one foot in this type of boat in America'. It was five to six years before bow hydroplanes were fitted in British submarines.

These after planes were called Submerged Diving Rudders. This nomenclature was used up to and including the C Class.

3. At first Holland No 1 a compressed air reciprocating piston engine was attached direct to the diving rudders to operate them. This was found to be impracticable and the engine was replaced with by a rack and pinion gearing, hand operated by shafting from a diving wheel in the control room. The pinion shaft passed through the pressure hull, some way forward of the diving rudders and it is stated that in Holland No 1, the rudders were connected to the pinion shaft by wire ropes. These wires were changed later to a single rod.

4. Regarding the compressed air engine originally fitted, the specification for the American boats stated that 'this engine was fitted with an automatic device to keep the boat horizontal and secure constant depth submerged'. A Vickers record suggests that this engine was fitted in the Hollands and in A1 but not in A2. All of these boats completed within a year of each other and if fitted, the engines were removed and the hand gear fitted before completion or soon after.

5. The A Class, B Class and C Class had similar diving rudders aft. The rudder area increasing with the size of the boat to 10ft² each in the A Class and 19ft² each in the B Class and C Class up to C30, whilst the angle of hard rise to hard dive increased to 70°. Although in the Hollands the two rudders were operated by a single rod from the pinion shaft outboard on the port side, this was increased to four rods, two port and two starboard, in the A Class but still operated from the port side only. In the B Class and C Class, one of these starboard connecting rods was deleted and a lead balance weight fitted inboard on the starboard hull-bearing shaft. See Plate 8. This was done presumably to bring the planes horizontal should there be a break in the control shafting.

6. Early in 1905 it was approved for hydroplanes to be fitted on the forward side of the conning tower in A7-10. They were called Conning Tower Screw Type. The planes were to have an area of 10ft² each, angle rise to dive 40°, with a total weight of hydroplanes and gear of 11cwt. They were screw actuated by a rod passing vertically from gearing on the plane shaft into the control room. This approval was certainly too late for amidship planes to be fitted in A7-10 during building and Vicker's records confirm this. B1, B2 and B3 were certainly fitted with this type during building as shown in Plate 5, B4 was not, B5-11 might have been and C1-10 were built with them.

7. In 1907 bow hydroplanes came into the picture and were fitted for trials in A3. Each plane was 12ft², made of double 7½lb plating filled with fir. The athwartship hydroplane shaft was 2ft 1in below the inside shell plating over the torpedo tubes and was operated through a rack, worm and bevel gears by telegraph shafting from the control room. It took 23 turns of the control room handwheel to put planes from hard rise to hard dive, i. e. 50°. A 25lb guard plate was fitted forward of and in line with each hydroplane. It was originally intended to have guards over the tops of the planes but there is doubt whether they were actually fitted. The total weight of hydroplanes and gear was 30cwt.

8. It is difficult to ascertain which type of hydroplanes, other than the after diving rudders, was fitted in the individual boats up to C10. A7-10, B1-3 and probably B5-11 had conning tower planes; A3 and B4 had bow planes and C1-10 certainly had bow planes and conning tower planes when first completed. However, by the end of 1907, experience had shown that 'the combination of bow and after hydroplanes was the best for keeping the boat horizontal when changing depth, instead of at an angle as previously. They also added to the navigational qualities submerged'. The combination of bow and stern hydroplanes became the standard practice from C11 onwards. It is logical to assume that the bow planes were fitted retrospectively in all the earlier boats from the A Class and conning tower planes removed where fitted. Although in November 1908, approval was given to fit bow hydroplanes in A2, A4-6 and A11-13, as in A3 i. e. in the boats not already fitted with conning tower planes.

A7 with experimental hydroplanes forward of the fin
A7 with experimental hydroplanes forward of the fin

9. In C1-18 Worm Submerged Type planes were sited forward with the main shaft right on top of the torpedo tubes and only about 8ft from the bows. See Plate 7. The planes had an area of 26. 5ft² each with an angle of rise to dive of 50°. A guard was fitted just above each plane. From C19 onwards, the planes were moved into the superstructure and were now called Worm on Top Type. They could not be housed but locking gear fitted. The guards were deleted. From C31 onwards the area of the after diving rudders was decreased from 19ft² in the earlier boats of the class to 11. 75ft² each. The bow hydroplanes must have been most vulnerable to damage in heavy seas.

10. In all classes, so far, the telegraph shafting from the control room to the planes was worked by hand. Electrical means for working the shafting were first fitted in C6 for trials. Electrical power operation was adopted in the D Class onwards.

11. Although little experience with the bow planes in the C Class could have been obtained, when D1 was laid down the siting of the planes in that vessel suggests that their position was chosen to take account of possible damage and the effect of diving. They were of Worm Submerged Type over 34 from the bows and well submerged at torpedo room flat level. Because of the change in the stern form from previous classes, the after planes were brought forward 26ft from the stern at just above shaft level. The reduction in distance between the planes in a 160ft long boat was excessive. In later boats of the class the forward planes were raised slightly and moved to within 9ft of the bows and the after planes were also raised and moved further aft.

Plate guards were fitted forward of and in line with both the forward and the after planes in D1. In the later boats a similar guard, but much larger, protected the after planes, but, because of the position of the forward planes, guards were seemingly impossible.

12. In D1, the angles of rise and dive were 50° forward and 70° aft as in the C Class. In D2-8 the area of each plane was increased from 30. 6ft² in D1 to 34. 5ft² forward and to 33ft² aft. The angle of rise and dive was 50° both forward and aft. This must have been seen to be a retrograde step and in the E Class the angle increased to 70° both forward and aft and became standard in future classes except in a few isolated cases which will be mentioned.

13. A major point of interest is that both sets of hydroplanes, starting with D1, were operated by 2hp motors. These motors were on the hydroplane pedestals and operated shafting connected to worm quadrants on the hydroplane shafts. The planes could also be operated by hand.

14. In the B Class and C Class, the after planes fitted had been called Submerged Diving Rudders. The bow planes fitted had been called Hydroplanes. In D1 the name After Hydroplanes was introduced. A simple change in name can bring its problems as the following extract from a letter written in August 1960 by Admiral Sir Charles Little, who had been the first Commanding Officer of D1, shows:

The initial dive (of D1 ) off Walney Island was not re-assuring, the vessel made large swoops up and down and it seemed could not be kept to a steady depth line. After some discussion a detailed examination of the after diving gear found the planes connected in reverse to what we had been accustomed to. The reason was easy to see, a misunderstanding in the drawing office. For the first time we had after hydroplanes in place of tail rudders and being hydroplanes the Drawing Office had connected them as for the bow planes which we already had in the C Class. We tried again and kept a fair depth line but it was not easy and unnatural to turn the after diving wheel the opposite way instead of chasing the bubble with the indicator move it away.

15. About 1911/12, consideration was given to the damage being caused to fixed hydroplanes from pounding in a seaway. It was suggested 'that they should be made in two parts', but great expense would have been involved. Reduced area was suggested but 'the behaviour of the boat when diving with helm over, does not encourage the belief that they could do with smaller planes'. All classes were apparently suffering from 'bow-up on turning' trouble.

16. However, the E Class had started to build and the pattern followed that in the later D Class except that the forward planes were brought further back from the bows and slightly lower. Although the forward planes were slightly smaller at 33ft² each, the after planes were increased in area by about 40% to 40. 4ft² each. The operating motors were increased from 2hp to 3hp each.

As a result of war experience in 1914 much larger guards with supports were fitted around the hydroplanes and these appendages caused a loss of speed of about 1. 25 knots in the E Class and corresponding losses in other classes so fitted depending on the speed. The guards were in the form of a tripod of three bars connected to the hull forward of the planes,

17. E14 and E15, which were laid down soon after the discussions mentioned in Paragraph 15, were fitted with hydroplanes of a housing type forward in the superstructure. They were on a turntable by means of which the planes could be rotated from the athwartships out position into a fore and aft position inside the superstructure as shown in Plate 14. It is assumed the planes were housed and vice-versa by hand. This undoubted experiment to overcome the damage to fixed planes does not appear to have been a success since no other boats of the class were so fitted. It is relevant that S1, which also had housing hydroplanes, had been completed in August 1914 a few months before E14 and E15 and she had a lot of trouble with her planes.

At the time the forward planes in E14 and E15 were called Turntable on Top Housing Type. The earlier boats had Worm Submerged Type and later boats Tiller Submerged Type, when the method of control was changed as mentioned in Paragraph 19.

From hereon the terms used are forward and after hydroplanes of the drowned type when fixed below the surface LWL and of the housing type when they can be completely housed within the superstructure or folded against the superstructure side.

18. The S Class was an Italian design and were in fact the first RN boats to have housing hydroplanes; they were fitted both forward and aft and were of Italian design. S1 on passage from Scotts to Portsmouth after delivery in August 1914 experienced difficulty with these planes. Extra supports were fitted and other means tried to overcome the troubles but they were never really satisfactory and reports of defects especially in the winter were' frequent.

19. The Swordfish had both the forward and after hydroplanes housed in the super­structure but the method of control then being used in the E Class was changed. In the latter the electric motors were on the hydroplane pedestals in the control room and these motors ran intermittently, that is when the planes were actually being moved. In Swordfish the motors were placed near the hydroplane shafts, ran continuously and were coupled with VSG hydro-electric power units. Scotts statement on these changes is as follows:

'When the steering and hydroplane gear for Swordfish came up for consideration, it was felt that something better than the purely electric drive previously used might be fitted for this purpose. After a considerable amount of original designing work on various alternative arrangements, the Williams Janney power unit was adapted for use on shipboard; the hunting gear and other details being worked out in conjunction with The Variable Speed Gear Co to make the whole scheme suitable for the purpose intended. Subsequently the E Class, G Class and K Class of submarines were similarly fitted. For the control shafting ball bearings were proposed and fitted on the Swordfish and later on this became the universal practice in submarines. '

To amplify these remarks by Scotts the valve actuating the VSG unit was operated by shafting from the control room pedestal. If the motor failed an electro-magnet automatically threw into gear a clutch which enabled the gears to be worked direct by hand from the control room pedestal. This procedure became common practice.

Swordfish, which was not completed until mid 1916, had little chance to test her housing hydroplanes in service. The changes in drive were noteworthy improvments. The improved drive was undoubtedly feeted in E17 onwards.

20. In the V Class and the Nautilus building at the same time as E14 and E15 it was originally intended to have similar housing type forward hydroplanes as shown on Plate 17, Plate 18 and Plate 22 but this was discarded and arrangements fitted as shown in Fig 6.2, Fig 6.3 and Fig 7.1.

In the V Class the planes were placed as in the E Class but control was by hand with no power unit of any sort. The area of each plane was 23. 6ft2 forward and 25. 4ft2 aft in V1 and the angle of rise to dive 50°, in V2-4 the area of the forward planes increased by about 10% and the angle of rise to dive to 70° both forward and aft. A point of interest is that the guards shown in Fig 6.3 appear to have serrated edges on the fore side as though for cutting wires or nets.

The Nautilus followed the E Class pattern and although a boat of over double the displacement, kept the same approximate size of after hydroplanes at 45, 6ft but increased that of the forward planes by about one-third to 44. 5ft2. The horsepower of the control motors was increased from 3hp to 6hp.

21. In the G Class it was intended to fit housing type planes forward and aft on account of the resistance of the submerged planes and guards on the surface, but the serious troubles in the S Class caused them to be abandoned and the ordinary type arrangements as in the E Class with the same control were fitted. The plane area was 35ft2 forward and 44ft2 aft each. The forward planes were very low in the tanks below the torpedo room flat obviously to give the maximum submergence possible. Due to this change the surface full speed as designed (before the war) of 15. 5 knots dropped to 14-14. 5 knots.

22. For the J Class a review was made of past experience. The increased resistance with drowned hydroplanes, and especially the additional guards, was now well known. Pumps and vertical jets and horizontal propellers above the superstructure had been proposed as means of obviating resistance. It is stated that 'this had been tried in an A boat early in the war and was shown to be useless for large submarines, ' experience with the Italian housing hydroplanes in the S boats showed they were far from satisfactory. After much consideration it was decided to fit the drowned type aft and the housing type forward. To house, the planes slid inboard along a shaft into the superstructure. This could be done hydraulically from the control room or by hand locally. It was accepted that the boat could be dived and navigated by the after planes only if the forward ones broke down. The control gear was of the Swordfish type. There seems to have been variations in the type of forward planes fitted in this class since Fig 7.4 shows for J7 a type fitted later in X1. See Para 27.

23. The K Class was as the J Class with housing planes forward of area 45ft2 and drowned planes aft of 80 ft2 each. Control was by 10hp motors. Guards were not fitted but for the after planes a wire extended from the outer end of the fore edge of the plane at an angle of about 45 forward where it was connected to the hull. In K26 the forward planes were moved further aft in the superstructure from those in the K Class by about 15ft and this was stated to be an improvement. The after planes were moved to a position in the stem fin with the planes just abaft the propellers. A loss in speed in K26 was subsequently blamed on the after hydroplanes being in the wake of the propellers but this was not the main reason for the loss. The M Class reverted to drowned hydroplanes forward and aft as in the E boats with plane area 41ft² forward and 60ft² aft each. The operating motors were of 3hp.

24. Although twin screw boats, the arrangement of hydroplanes and rudder aft in the H Class was the same as in the single screw C Class. The forward planes were in the superstructure above the forward end of the torpedo tubes and folded forward into recesses in the sides of the superstructure.

25. In the single screw R Class with a very fine circular form aft, the propeller was placed at the extreme after end and the hydroplane shaft about 6ft forward of the propeller near main axis depth. The outer edges of the planes were held by pintles in large horizontal fins which were necessary for submerged control with this type of form. The fins formed very good guards to the planes. The forward planes were well submerged below the level of the torpedo tubes and were fitted with a very small guard forward of each plane. The angle of rise to dive was 60°.

In the design of this class it appears that consideration was given to fitting additional emergency planes amidships designed to bring the boat level should she through any cause dive at an angle when going at high speed submerged, but this idea was not adopted.

26. The after planes in the L Class were at the extreme after end as in the H Class and had an area each of 42. 5ft². The forward planes of area 31. 8ft² each were of the drowned type under the torpedo tubes. Control was by 3hp motors. The frames of the hydroplanes were of cast steel with 7½lb side plates, the whole being filled with light wood or water excluding compound,

27. In X1, the forward planes returned to the superstructure position and were shaped rather like the quadrant on an ellipse with the forward end forming the axis and the inboard side parallel to the casing. They rotated aft to stow side by side in the superstructure. Their operation was performed by the same motor as was used for the forward LP blower and the capstan A end. Guards were not fitted. The after hydroplane shaft was in the stem fin with the planes in line with the propellers and had an angle of rise to dive of 60°.


28. In Oberon the forward planes reverted to the drowned type well submerged under the rear end of the torpedo tubes with the after planes in the stem fin position.

29. As will be seen from the above resume the difficult decisions had been whether to fit fixed or housing type hydroplanes, whether they should be in the superstructure or submerged, and also the depth of submergence. The disadvantages of the fixed drowned type planes were vulnerability to damage from pounding in a seaway or when coming alongside, and their resistance when on the surface with adverse effect on surface speed. The big advantage was their immediate effect when starting to dive giving better diving times. The advantages of the housing plane were improved surface speed and reduced risk of damage when housed on the surface, but it was more complicated with more parts to go wrong and with added weight, space and cost. If in the superstructure it was less effective in the diving operation.

30. The problem was accentuated by the fitting of effective hydroplane guards found necessary as a result of war experience and which were required for protection against mine wires and nets. In principle, guards or similar protection such as the horizontal fins in the C Class type of stem were required to meet these requirements whether the planes were of the fixed type or housing type. Because guards themselves were liable to damage and because of the price to be paid in speed the policy regarding fitting was often not adopted, the more so as the war receded.

31. Summarising the situation so far, after hydroplanes fitted at the stem fin in line with the propellers had been introduced in K26 and followed in X1 and Oberon. This arrangement was adopted in Odin and later Class. When, in the early 1930's, trials were arranged for a Rainbow Class submarine to pass through nets, a special guard had to be fitted to protect both the propellers and the after hydroplanes.

There had been many changes in type and position of the forward planes before arriving at the L Class with drowned planes very low down under the torpedo tubes and fitted with guards. Then followed the H Class with planes hinged to stow against the superstructure side, X1 with superstructure housing type and Oberon as in the L Class. By the time Odin was designed no experience had been possible in X1 or Oberon but considerable damage had been sustained by both planes and guards in the L Class. This would appear to have swayed the decision for the Odin Class to fit housing type at superstructure level, the planes folding upwards against the superstructure sides. This arrangement followed in later classes. Guards were not fitted.

32. In the 1920's telemotor control for hydroplanes was adopted. A partial step in this direction had been made in the old Swordfish in 1914 as mentioned in Paragraph 19. Now in the Odin Class the hydroplanes were telemotor operated from the control room each pair with its own VSG unit and motor. The control shafting was dispensed with. This policy continued in later classes except for the Swordfish Class which retained the control shafting. The forward hydroplane housing gear was operated from the main telemotor system.

Because of the noise made by the VSG units it was decided in the late 1930's to operate the hydroplanes off the main telemotor line and abolish the VSG units.

33. Returning to the now standard practice of fitting the stem hydroplanes in the stem fin. In this position they are less liable to be damaged in a following sea or when coming alongside than planes higher up in the hull as in some of the earlier boats. However, the mechanical portion of the gear is inaccessible afloat and the question was raised in 1935 as to damage to this gear by the shock of bottoming and also damage to the planes due to touching the bottom. The stem fin is an extremely strong structure and would have to receive a very heavy shock to damage the operating gear within it. The following table was prepared showing the angle that had to be taken on in various classes for the stem fin and after hydroplanes (at 20° dive) to hit the bottom.

Bottoming angle in degrees
CLASS Stern fin After Hydroplanes
E 21½
L 50 8
L 4
M3 24¾
K26 4


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Chapter 19: Diving DepthChapter 21: Rudder and Steering Gear