Hugh, The reason fins are on the forward section of larger submarines are twofold: 1. For low speed operations the moment arm creates a larger force to change the course of the sub as compared to locating the planes on the sail. 2. For under ice operations, the planes can be made to retract so as not to be damaged when surfacing through significant layers of ice. A high-aspect ratio fin with a thickness of ~40% of the chord using a profile similar to a NACA 65-020 foil is most effective. I have sketches from one of my classes if anyone is interested. R/Jay Resepectfully, Jay K. Jeffries Andros Is., Bahamas Save the whales, collect the whole set. From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org] On Behalf Of Hugh Fulton Frank, Thanks. I‘ve just spent the morning on the lathe making new hydraulic motor mounts out of stainless. I kind of like the look of the Hammerhead shark. He has his dive planes way out in front! That way they don’t need to be so big. It wasn’t me on the snap roll thing. I am still trying to get my head around that one. I think it may be something to do with the aerofoil shape. Fish and larger subs all seem to have their dive planes forward of half way. Porpoises have two sets one at the 1/3 mark and then the other at the back. I’ve got my money on your design being all right in the real. Chs, Hugh |