A seaplane is a powered fixed-wing aircraft capable of taking off and landing (alighting) on water. seaplanes that can also take off and land on airfields are in a subclass called amphibious aircraft.seaplanes and amphibians are usually divided into two categories based on their technological characteristics: floatplanes and flying boats; the latter are generally far larger and can carry far more.. The twin vee boats float high, so high that they can plane on one engine in less than 3 seconds.. Running on one engine is definitely saving fuel: friction losses in one engine, gearbox and auxiliary equipment is reduced by 50%. the actual gain is a bit less because prop slip increases due to the higher blade load and there is some extra rudder resistance, but is still significant..
A twin engined boat is designed to perform with two engines and will be difficult to manouvre with one engine. apart from that it is bad for the engine & gearbox of the engine not being used to be dragged along which is why our sailing chums have a feathering prop or a means to stop the shaft rotating whilst under sail.. I know on a large outboard center console or race boat. the third engine adds at best 13 mph, and the 4th adds only 7mph say for a boat with twins that does 45-65mph with twins. extra engines and drives will help with getting a heavy boat or heavy load onto plane and out of the hole.. In south africa, trailer boats that travel more than five miles offshore must have two outboards and be able to plane on just one, so the authorities there obviously acknowledge the safety.
