Like everything you have to start somewhere,when I first started building these boats I thought they were the bogs dollocks, Looking back now I have to question the glue I was using? These first boats have clockwork motors and do sail but they dont dive also the stern glands leak, Bottom right is a boat which I fabricated from a copper boiler,on its maiden voyage it sank sadly killing the entire crew.
Building them however was a good way of trying different hull designs and ironing out various glitches.
The breakthrough came when I realised that the only way to control buoyancy was with an internal ballast tank. The development of the tank system means that the boats are able to be trimmed to neutral or negative buoyancy. Ideally the subs need to be just above neutral (nearly sinking) so the forward motion submerges the boat and then it resurfaces when the motor runs down.