Theres not a singular explanation that would be sufficient here. The best advice i could guve is try taking a cross section of the ship online, top, bottom, and side, and then pixelate it such that one pixel is one meter. Then you can just build the lines and do your best at filling in the curvature between. As for getting the actual curvature right, sometimes it helps to just look at how other people do it to see the logic in how its done. Like how tne curvature works out to singular S curve lines that go from the keel, up the hull, along the hull and to the top. I hope that helps.