@General_Dave_1
There is completely no need to use gradients.
Of course, SB shading of hulls is a rather vague matter, but there are certain "usual practices". Back in the day not too much attention was attached to representing the cross-section of the hull, so sometimes just a 1-2-3 pixel thick darker stripe was applied along the bottom edge (keel) - and sometimes brighter stripe along the upper contour, if relevant - to show that said place is rounded (and not of square-ish cross section). Over time, though, the so-called "45-degree rule" gained popularity (though it's not mandatory), which generally says that brigther/darker shade is applied if the surface is facing the viewer at an angle equal or exceeding 45 degrees (sample shown on drawing below under number 1)
As for the Skate, "your" shade goes (unusually for SB) from roughly middle of the hull. I wasn't looking too hard for detailed plans of this submarine, but quick look into google gave me this:
https://live.staticflickr.com/7692/1705 ... 1b12_b.jpg
Applying the 45-degree rule, IMHO the shading would
very roughly look like on the drawing 2 (and I mean rather general concept than specific number of pixels at specific places).
Finally, regarding the Barracuda. Indeed, sources seem to be scarce, but as it is, the bow is represented like it wasn't rounded at all in front (along the vertical axis), and shading of the bottom, which is getting wider towards the bow would suggest that it's shape is like on drawing 3 - mind it's not to scale and only meant to represent the general idea, not the pixel-by-pixel details).