i was working on this but ...
i didnt finish it ... most s-boats where painted in black, and i had some problems working on dark colors in SH4 because the in game lighting changes the colors depending from where you are looking at the boat, also the mapping is real bad , like the hull uses the same texture as most of the deck parts as you can see below i made an experiment painting the hull in a bright color so i could see what it afectted it turned out like this
the purpose of this was making some versions of the 1920's 1930's S-boats that had under the water line painted in brick red , this and the fact that sh4 uses reflective textures would make the numbers in conning tower apear backwards on one side made me give up ... also the alpha layers arrgghh