What are the factors determining position of forward dive planes on a submarine?

Question

This question is restricted to nuclear submarines.

The forward horizontal dive planes of nuclear submarines may be located either on the hull in front of the sail (as for seen in this cutaway of an Astute class submarine or on this pitcure) or on the sail (as seen in this picture of a Rubis-class submarine). I fail to see a logic in this location (I tried to see correlation with size, role (SSBN, SSN) and designed year). Here are some of the submarine classes that I took into account:

• located on the forward hull:

  • Virginia class
  • Astute class
  • Vanguard class
  • Seawolf class

• located on the sail:

  • Los Angeles class
  • Triomphant class
  • Columbia class
  • Delta class
  • Type 094

As I failed to find any logic, I suppose there is no clear advantage of one location over the other. My question is: when designing a submarine, what are the criteria taken into account to decide the location of the forward dive planes?

Answer 1

One consideration is that the location of any forward dive planes are based on internal dimension considerations, as well as mass locations and the positioning to reduce noise production, transmission and amplification.

A good study that you might try modelling in CFD especially as external factors such as thermoclines will affect the results.

Answer 2

This is a complex design decision, with several factors being considered:

1. Fairwater planes (located on the sail and sometimes called sailplanes) give the easiest depth control because they don't put an angle on the ship. So stern planes are used to put an angle on the ship for large depth changes and the fairwater planes manage small changes. These planes require a larger sail to fit the planes and hydraulics. Think US designs versus the smaller Soviet/Russian designs.

2. Fairwater planes are also in a terrible place for surfacing through arctic ice. These planes must be rotated to vertical and be strengthened to deal with surfacing through ice. The additional mechanisms and strengthening add complexity. Early US 688 subs could not surface through ice for this reason.

3. Bow planes free up space in the sail. You now have a more complicated depth control system, since bow planes will put an angle on the boat. Ostensibly, you should be able to put an angle on the boat faster, which would be good if you want to do this or bad if it happens when you don't want it to. At high speeds, newer US subs (that use bow planes) at high speeds lock the bow planes and use split stern planes to limit the problems that could be caused by plane failure.

4. For under-ice operations, bow planes need a method to either fold or retract. Both will require space inside the outer hull.

So really, it's a decision by designers and operators over how they want to build and use the ship. There's not a single right answer. It can only be decided in the context of the entire ship and how it is used.