Thinking about it a cat is the way to go, as the solar panels are very heavy and need to be flat for max efficiency. A cat would give you the stability you need. unless there is a need for the project to incorporate a spring, it may be best left out..the drive from it would only cause drag unless retracted. A space frame could easily be made from kite rods and sockets made from aluminium tube bits welded together, and epoxied to the rods, megga stiff.   Ashley

Hi Rowan,

Any chance you can put some photos on the forum ?

Len.

Len,

No, sorry but it can’t be done.

Vinnie

Rowan. I would have thought that having a cat would be better than a hull and two outriggers, from a drag point of view, as the outriggers do not contribute to the floatation of the overall mass, they just add drag…unless they are so large that they DO add floatation as an integral part. What comes first..the motor or the prop…good question. i think that in model boat building the prop comes with the hull and style of vessel…for instance if anyone was building a modern warship of so and so dimensions, then a prop of approx so big and of such a style for that vessel/navy would be chosen, in proportion to that normally used on a full sized vessel. Undoubtably a large prop turning slowly is the most efficient, and so you would want to go with that basis. How big ?? it might be an  idea to talk to the man at the "prop shop" –Simon is it?(help me out here chaps)  as he designs props. No doubt he will want to know what power there is available. The prop for the electric motor on a known gear ratio would be easier, as the engine power is known and the overall RPM could be calculated and so a prop could be chosen on that basis.

I was going to suggest using a bulbous bow, as this gives an improvement in hull efficiency…up to 15% I have read at cruising speeds, or even trying a semi submersible twin hull arrangement, however you may actually be going TOO slow for these devices to be effective.

Perhaps a Kort nozzle might help? no experience of them myself, but they aid low speed push apparently. Having two props near each other might not be a good idea, as one might interfere with the other (and you dont have much power to play with) so siting of these items needs to be considered…again easier on a cat, not so easy on a monohull. Is this craft required to be radio controlled or a simple free runner???

Ashley

why dont you try putting some plastic bottles around the edges as that will help with bouyancy problems

Yes,

you jam in the biggest motor you can! 

Len  

Two things that might help the research in to the alternative propulsion – first go back in time and see if anybody has copies of magazines pre WW2. It was common in the early 1900’s to have boats powered by clockwork springs and any photos you could find might give some idea of prop size. The second idea is why limit yourself to a water prop? If I was wanting a lightweight reliable propulsion system I would be trying an air prop driven by strands of rubber as some of the old model aircraft were. You would need some sort of lock that was radio controlled so you could release it when required but my memory of aircraft with multiple long strands of rubber wound up with an old eggbeater hand drill was that they were powerful and ran for a long time relatively speaking. It never hurts to think outside the square. Cheers, Ian.