Surface Drive - propeller protection for beaching

Hi Drew,

I can feel your pain... the same problem here as I have started as you did with the thought of building or modifying a tritoon but than I just starting seeing the same problems as you did. As I want to transport 15 people on board the raised deck and handrail is a must... the outboard is out of question due to economics and what I am left with is a dream...

A nice evolution you got there in your design. I like the catamaran with covered surface drives. My problem with catamaran boats is that I would like to use one engine only ant that's impossible for inboard diesels.

After a lot of research and reading I have envisioned the ideal boat:
- m-hull just like the workboat I have posted above (luckily I found someone here in the forum that know the owner of that boat so I asked for some details... hope to get them soon. First impression is that the owner really loves the boat and the way it is handling rough water an payload)
- power-vent propulsion - I have contacted power-vent but I am not sure if they will reply. It's a pity all this patents keep this innovation out of reach for most people. I would also need to fit the power-vent system with a sandshoe to protect the prop as I was describing in my first post
- the engine should be a keel cooled 300-350 hp with dry stack as the boat will be driven sometimes in shallow muddy water. A V6 from Toyota or a V8 fro VW would be nice .

For the moment I am waiting for some answers from m-ship and power-vent to see what their conditions are for licensing etc. but I fear the worst...

The deck will be just a flat deck with benches, a bimini top, a toilet and drivers sit etc. Simple and efficient but has to be reasonably priced.

So the surface drive seems a good way to go for you. You might try to ask M-ship for the blueprints of that workboat too... maybe being an American they will listen to you ).

All the best,

Daniel

 

There seems to be a mis-conseption that surface propulsion gives a shallow draught operation.That is not necessarily right for all round good performance.
If you want good steering with s/p.. a deep rudder set down into the denser water area is needed,taking you back to conventional drive draught. Some s/p
drives do have a deep dagger rudder. When a propeller is operated in shallower water a bigger prop is better and also a deeper rudder.

 

Hi Tom,

I know about the bigger rudder and conventional prop and I know the boat closest to that requirement is the Rescue Minor but that is not a planing boat and it can not do more than 25-30 km/h plus no one has build a bigger version and you would have to go uncharted territories.

My idea is to use the power vent type of propulsion as it uses the same tunnel drive as Rescue Minor does but in a ventilated mode. When the boat is at low speed the hole prop is submerged and there will be enough thrust considering that the prop will be much bigger than a conventional one. The rudder can be bigger I suppose with not so much influence on the performance at speeds between 30-50km/h. Hence the two step rudders used in surface drives. The only downside is that you have to have power steering to control that rudder.

Using a conventional prop in a tunnel is complicated and can give you a lot of trouble (ask CDK) especially in fast boats.

For the moment the set-up of Power-Vent with sandshoe and bigger ruder used in a planning hull seems to be the best way to go, for a fixed shaft surface drive running at slow speed in shallow water.