Steven, you are correct about the efficiency of the pup and motor. Those two things have the least loss in a Hydraulic system. The big issue is the energy it takes to push the oil
through the hoses. Then you have to have flow controlls, pressure reliefs and the fact that whether the hyd.motor is turning or not, the pump is turning and pumping oil
of which is being pumped through the system back to tank. A system can only be hopeful of 50% efficiency in reality. And then add the energy being wasted while the pump is running. Add to that the noise
. They make a very noisy system and most likely would drive most boaties nuts.
However, Hydraulics have their place. Kinda like a Plane vs a Helicopter. Both fly, one is far more expensive to run than the other, but each have their own purpose that neither can fit the others role of.
Here is an example of what can be done with hydraulics. These propulsion
devices have big Cats powering them. The props are on hydraulic motors and the entire motor/prop can be spun around 360deg and the entire system can be raised and lowered. http://www.cruisersforum.com/gallery...p?i=4595&c=517