Well, a 12-volt motorcycle battery or one of those smaller gel-batteries might do the trick.electric trolling motor with 12v deep cycle battery would be plenty to push a little sunfish safely to port. A lot of extra weight to carry though.
All good thinking!I'll draw a sketch this weekend. It would sort of look like a Sunfish stuck under a Catamaran. Objective would be to make something a cheap a possible yet sturdy enough to last the whole season. The trick is to find something in the junk pile that would work as pontoons. If I did not think it would be stolen I'd say mount the motor on the rudder bracket and when you are ready to sail, remove it and place the motor in a water-proof container with a bicycle flag on top and let it float till retrieval. Perhaps mounting the motor in a foam cooler chest with the lower unit stuck through hole in the chest and strapping the chest to the Sunfish? That's about as simple as I can think of.
I would look into a mount to the rudder for the motor/prop.
Kind of stealing the idea of one of the modern high end trolling motors that mounts to an outboard...
Engine Mount
And I'd go with RC model aircraft LiPos for power (because I have a lot of them and they are VERY light.)
Use of a common RC electronic speed control and a "servo tester" as the throttle control would allow use of a modern brushless motor (small, light and inexpensive.. and they do fine running underwater in fresh water if you dry them out afterward)
Some creativity and I could rig this all up and be lighter than that drill rig and have more power... (I have up to 5000 watt or 6 hp motors available..)
the expensive part of all this is the batteries if you were to go out and buy everything needed.
And easy to install/remove...
Would a 9-volt brushless motor be compatible with my 9.7 volt Makita batteries? (This would be a freshwater application).
The motor should work with the batteries.
A brushless motor requires a brushless electronic speed control and that would need a method to operate the throttle.
My point was to have some additional poop to beat the cell home. (I should have lowered the sail, and used the "bare pole" to get me home)."...If there is enough wind to bend the mast the drill is not going to have enough poop to do anything..."
The Sunfish shouldn't need 2-HP to move reasonably fast, but my take on the above advice is that a brushless motor powered by a 9.7 volt Makita battery isn't going to be efficient.Actually... get the ESC rated for 10% to 50% more current than the motor. The size prop will be dependent on the motor power... and with a 9 v rated motor its probably going to be small. (probably too small to move the Sunfish). I'd expect to need a 1500 watt minimum (appx 2 hp) and probably want 2500 to 3000 watts to be able to "motor out" at a reasonable speed. Its not going to spin a standard trolling motor prop. Its going to spin an RC boat prop. Much smaller and much faster RPM and very inefficiently.