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  #16  
Old 01-02-2011, 07:34 PM
yodani yodani is offline
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Quote:
Originally Posted by claydog View Post
Right now I'm thinkin 25-30 foot aluminum Cat with twin 150 hp 2 strokes attached to surface drives.

I started out with the thought of modifying an existing pontoon boat to suit my usage as there are 100s of used ones for sale within a couple hour drive of my home on any given day. A 25-30 foot pontoon with 150-200 hp it would be good about 70% of the time for fishing/family/friends on inland lakes and rivers. The other 30% is fishing 3-5 miles off shore on the Great lakes in calm weather. To do that with a pontoon I would want the deck raised 6 in to a foot above the stock deck height, then I would want to sheet the underside of the deck and deck risers with aluminum to reduce drag and help handle the bigger chop on the Great lakes. Once I raised the deck, the motor mounting system would have to be lowered to match the raised deck. At this point starting with a clean sheet of paper seemed like a good idea.
The 2 main problems I have with pontoons is that the power head of an out board or the doghouse of an I/O is an inconvenience at best for fishing off the back and in the way of loading kids and their tubes/skis/wake boards on the back. I also feel that the best looking pontoons have about as much aesthetic appeal of a farm tractor with custom paint. To clean up the rear deck space, and since Id be moving the motor anyway, I thought that going to twin jet drives (maybe from a PWC) mounted in the rear of each pontoon would be a slick solution for rear deck space. That led me to a Cat hulled boat and having little personal experience with jet drives I found my way here and am now learning about surface drives .


regards Drew
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
Attached Thumbnails
Surface Drive - propeller protection for beaching-m-hull_04.jpg  Surface Drive - propeller protection for beaching-m-hull_01.jpg  Surface Drive - propeller protection for beaching-m-hull_03.jpg  


Last edited by yodani : 01-02-2011 at 07:38 PM. Reason: Added picture of M-hull
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  #17  
Old 01-04-2011, 08:45 PM
tom kane's Avatar
tom kane tom kane is offline
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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.
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Surface Drive - propeller protection for beaching-tunnel-s_p-mode.jpg  
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  #18  
Old 01-05-2011, 04:03 AM
yodani yodani is offline
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Quote:
Originally Posted by tom kane View Post
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.
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