Talador,

  I agree on the second plate to smooth the flow when the prop is deployed, and also raising the motor high enough to be clear of any water when stowed.

  You make a good argument for going with an outboard -- a single 20 hp Honda outboard costs less than $5,000 and weighs 130 pounds.  At that weight and cost, you could even stow a complete second motor in a vacuum bag should the first one fail.

  The equivalent electric setup might be closer to $30,000, weigh nearly 1,000 pounds, plus require multiple "real" holes in the boat that could leak.

  A motor in each hull would be handy, but it may more important to a catamaran than a proa with two deep foils that can counter-rotate.  Plus, with a single motor, everything can be kept in the lee hull.

---

  A motor-in-well related admission: I'm currently building a 26' plywood dory that's being built around a 27 HP Yanmar outboard diesel in a well. 
 
  Basically, I fell in love with that motor, found one in Missouri with only 24 hours on it, and decided to build a boat around it.  Since it would be silly to hang a 300-pound motor 27 hp motor off the back of a planing skiff, I went with the dory shape.  It won't care about the weight in the slightest.  That, plus the dory has nice salty lines.

  I'd consider an outboard diesel in a well for a proa, but Yanmar doesn't make these any more, and I'm not sure there's a clean replacement from other manufacturers.  There are plenty of diesel outboards in China, but I'm not sure I'd want them running inside my lee hull.  For that matter, I'm not even sure I'd want the Yanmar in the lee hull -- I don't yet know how much smoke will make it up from the underwater exhaust into the well.

        - Mike

 

Mike, - " I would go with a retractable motor, in a tall well, with a hull section mounted below its cavitation plate so that it presents a smooth surface when retracted. "

Definitely something to seriously consider, except that I would make the cavitation plate fit the floor and seal it off when the prop is deployed too : )

I like this solution better than the outboard in the pod, except for the flooding in the sealed hull section. I think that the prop needs to be retractable all the way above the water line.

On the other hand, a diesel and sail drive is going to be a lot simpler and more reliable, Just the permanent drag of the prop : ( is a problem.

Mike - "The key is not to just get a maneuvering thruster that will overheat in 20 minutes, but one that is designed for use as a main propulsion unit.  Some are even used in tugs, ferries, and commercial boats."

Don't forget locomotives, big trucks, etc. and the regenerative power of a generator in the water when under sail.

Here is the bottom line with electric power, lets say the hp required is 30 hp.  That is roughly 22K Watts, which requires a 30KW generator.....  and we are off to the races cost and weight wise.

Typically a cat will have two 30 hp engines.

Talador