Displacement (as opposed to planing) boats are impractical to drive over 1.34 times the square root of the waterline length. That means you are unlikely to go any faster than about 4 mph. You could do this easily with a medium size trolling motor with a fairing and a better prop. This would avoid all the issues you are asking about. Two motor mounts, thrust bearings, packing glands, shafts, struts, etc will probably cost 5x one decent 50# thrust 24v trolling motor. Plus it will work perfectly after you take 20 minutes to clamp it on and connect two wires. Engineering an inboard installation is an expensive and complex job, there is a reason outboard power has 100% market share in the under 100 hp skiff market.
If you are really determined to build an inboard setup Glen-L has a good book about inboard installations. It's more aimed a the V-8 ICE crowd but you need most of the same parts they do, just smaller.
Also you would be much better off with a single prop and rudder. Half the cost and complexity and more efficient. One big prop is much better than two smaller ones. Dave Gerr's "Propeller Handbook" is the bible.
Good luck with your project.
Denny Wolfe
www.wolfEboats.com
On 3/19/2011 11:02 PM, stollte wrote:
Hi everyone!
I'm new here and this is my first boat build. I built a small (7' 6") two sheet boat(I'm surprised how well it turned out) and now I'm considering using two scooter motors to propel it. I figure with two props in the back I could steer by varying the speed of ether motor or even reverse one to turn tightly.
I'm good with the electronics so I'll have no trouble making a motor controller etc. I just need help on the boat part as I'm a total beginner.
My questions, to anyone who has any ideas or knowledge.
a) How do I run a shaft through the hull without leaking water?
b) How deep/what angle does the prop need to be for effective thrust?
c) How far from the back of the hull should the prop be positioned.
d) anything obvious that a beginner would miss.
e) What kind of torque is typical of a trolling motor, rpm, picking a prop etc?
Any links to DIY inboards for really small boats would be helpful and anyone using a scooter motor.
Comments suggestions are appreciated.
Thanks!
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