In WWII the Germans built a large number of big PT boat type craft called fast boats. Here is one I am working on in 1/72nd scale by Revell Germany. I got the bridge area done in this photo.
I cut the hull in half so that the boat would be waterline. The big trick is to align the location where the cut will go for the waterline.
The directions are are step by step with drawings rather than any written instructions. They are pretty good, but test fitting is essential.