All tutorials are good, Overally your technique has nothing wrong in it, its good way to do things. Its only proplem is that it really does require quite good references, specially in terms like good pics of the ship (or a model) that shows the entire hull, or cross-sections from most of the frames. Naturally thats not possible to have from all ships, thus we cannot make this type of drawing the ultimate rule, since it would basicly mean, underwaterhulls to be offlimits in all cases except the ones mentioned above. Thats why I added into the rule the part about shading underwater hulls according to their real shape IF ONE KNOWS what he is doing. That means you can use this method (or other similar way) alongside with the more original SB method of underwater hull shading.
this is EXACTLY what I have in mind myself
if it is possible, I would even make it an rule to NOT do this kind of shading unless you know what you are doing for ships uploaded to the main site.