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Home - Dits & Bits - BR3043 - Part One - The Individual Classes - Chapter 2

Chapter 2: Standard Particulars of Submarines

2.1 Introduction

1. Very little information was released at the time about the early classes of submarines and what information was published was not explicit and was often distorted. Even in the Admiralty, detailed knowledge of the Holland boats was quite limited by modern standards until after the first boat had been delivered.

2. The Holland boats were of American design. Some American practices were used by Vickers in the Holland and following classes until about 1914. The American practice differed from the Admiralty practice. As a result various authorities gave varying figures, especially for dimensions and displacement, and this continued until Admiralty practice was generally adopted. Some of the items, which caused confusion, are mentioned below.

2.1.1 Frame Numbers

3. American practice was to number frames from aft commencing with number 0 and was used in the Holland Class to E Class, in the S Class, V Class and W Class and in Nautilus, that is in all classes which started to be laid down before mid - 1914. It was also used in the K Class (1915).

The Admiralty practice of numbering frames from forward started in the F Class and G Class - both Admiralty designs - in 1914 and continued In all classes thereafter, except in the K Class.

In those boats numbered from aft Frame 0 seems to have had no defined position. It was at the after end of the pressure hull in the Holland Class and in the after trimming tank 4ft forward of the after bulkhead in the A Class and 3ft in the B Class and C Class. In D1 the after end of the boat is shown as Frame No 4 but this may have been because of some change in shape of the after end from the original design, the original frame numbering being retained. In D 2-8 the aftermost bulkhead was frame 0. In the E Class frame 0 was about 9in forward of the after end of the pressure hull.

The Admiralty practice was to start frame 0 at the Forward Perpendicular (FP). But there were variations from this rule; in K26 Frame No 1 was 14.1ft from the FP; in the H21 Class frame 0 was 11ft aft of the FP. There were other cases in which changes from the original design were made and the original system of frame numbering retained.

2.1.2 Perpendiculars

4. An early reference on submarines gives the Forward Perpendicular as at the stern where it cuts the load waterline and the After Perpendicular as the vertical through the centre of the rudderpost, this was Admiralty practice. A different interpretation was used in American designs and early on by Vickers.

In the early boats the perpendiculars were generally taken at the foremost and aftermost bulkheads, which could be the boundaries of the main pressure hull or even main ballast tanks. There were slight variations from this rule. There were also variations in later classes supposedly following Admiralty practice.

With these variations it is easy to understand how different authorities quoted differing figures for length other than length overall. In addition there were obviously differences in design and as built figures, which applied also in beam, depth, draught and freeboard, which caused confusion in quoted figures.

2.1.3 Displacement

5. The early spindle hull boats had a certain amount of positive buoyancy when submerged. After surfacing by blowing main tanks they often discharged auxiliary ballast water on the surface to improve seaworthiness. The surface displacement given was therefore at times less than the submerged displacement minus main ballast water. In some cases the main ballast tanks could not be filled completely. Later on in some classes emergency oil fuel was introduced into main ballast tanks. There was naturally some confusion in calculating and comparing surface displacements between classes.

In vessels with controlled free flooding spaces, especially in the double-hull boats, the submerged displacement quoted depended on whether the capacity of these spaces was included in the submerged displacement or not.

2.2 Standards to be followed

6. Because of the variations in figures quoted by various authorities, especially before 1920, an effort has been made in the text that follows and in the Appendices, to bring all classes to the same standards to allow a better comparison between classes. Mention is made in the text of figures quoted in the past where they differ to any extent from these standards which are based on modern practice (1930).

Definitions of these standards together with their abbreviations, where relevant, are:

  • LWL Load Waterline. The length on the waterline in the normal surface condition.
  • FP Forward Perpendicular. The vertical where the stem cuts the LWL.
  • AP After Perpendicular. The vertical through the centre of the rudder post.
  • Loa Length Overall. The extreme overall length of the vessel plus appendages where applicable.
  • Lbp Length between Perpendiculars. The length between the FP and the AP.
  • Lph Length of Pressure Hull. The length between the forward and after bulkheads of that portion of the hull which is designed to withstand full diving depth pressure. This will include trimming, auxiliary and internal main ballast tanks but not external main ballast tanks tested to 25lb/in2 or below.

2.2.1 Submerged Displacement

The buoyancy of the pressure hull, appendages and tanks in the externals built to pressure hull standards (i.e. all spaces capable of withstanding full diving depth pressure when closed to the sea). Plus the capacity of all external main ballast tanks plus the buoyancy of tanks such as fuel tanks which are external to the pressure hull but which can be pressure compensated to withstand full diving depth and remain full on the surface. It does not include free flooding or controlled free flooding spaces not fitted with HP blows. In the classes from the H21 Class onwards in which bow buoyancy tanks were fitted with vents and HP blows the capacity of these tanks is Included In the total main ballast water and is included in the submerged displacement.

2.2.2 Surface Displacement

The submerged displacement less the capacity of main ballast water used. In the Holland Class, A Class, B Class and C Class with a positive buoyancy when submerged the surface displacement is the submerged displacement less both the main ballast water used and the positive buoyancy. External main ballast tanks are taken as empty.

2.2.3 Standard Displacement

The surface displacement, less oil fuel, lubricating oil, fresh & distilled waters and ballast-water of any kind.

  • TPI Tons per Inch change in draught.
  • MCTI Moment in foot - tons to change the trim 1inch.
  • GM The metacentric height in the surface condition. From the Parthian Class onwards it is also used for the metacentric height in the low buoyancy condition.
  • BG The metacentric height In the submerged condition.

2.2.4 Reserve of Buoyancy

The total main ballast water used divided by the surface displacement. In the case of a vessel with controlled free flooding spaces it is the capacity of these spaces plus the main ballast water used divided by the surface displacement. In the Holland Class, A Class, B Class and C Class it is the main ballast water used plus the positive buoyancy submerged divided by the surface displacement.

7 It often happened that changes were made between completion of the design and building and in consequence there were differences between design or legend and as built figures and from old records it is often difficult to distinguish which figures are being quoted. Where known for certain the fact is stated in the text. In addition, especially in the later classes, some authorities quote a service condition. This covers the fact that the surface displacement will generally be slightly more than the figure obtained by using the definition in Paragraph 6 above since there must be, by the nature of the construction of the main tanks, some water left in the tanks after they have been blown.

8 Difficulties arise in obtaining comparative speed and endurance figures. Legend figures are worked out for a trial condition with clean bottom. There were often changes in the fuel carried and displacement between the design and as built stages. Later on appendages increased after completion of the design which had a considerable effect on speed and endurance, both on the surface and submerged. In the later classes operational figures for speed and endurance are given. These operational figures are with a moderately clean bottom, which caused loss of speed and endurance from the legend figures calculated for a clean bottom.


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Chapter 1: IntroductionChapter 3: The Spindle Hull Types - Holland, A, B and C Classes