You are right, servos for Schottle drives are heavy duty servos, with metal gear and BB. I have there not so expensive Hitec 645 BB MG servos, working good. I did not used in my Tito any plywood, I do not like this material for ships, I make new deck and everything exposed to water by fiberglass, 0,8 mm thick. In the hull are installed two ballast tanks, instead kilos of lead.I make them also from fiberglass. On the bottom of the hull are openings- inlet for water, on the top is vent pipe. Water is 2 cm below waterline, so they are full all time. I am happy with this system, water is everywhere for free, lead is always problem.