Solar boat

thank you all for your great input. We did have one question. On the canoe if we go with a direct drive motor, at what angle should the prop be relation to the bottom of the boat?

 

Another difficult question. The lower the prop slip, the more important a horizontal prop becomes. Many sailboats operate at 15-20 degrees drop angles. That works because they are high slip. If you go for higher efficiency and lower slip, you want less than 15 degrees, and ten would be better. But it's hard for me to think you will get the slip so low that you could tell the difference between anything less than 10. At that point you have to consider all the drag contributions from the shaft and worry about bearing spacing and such since shafts tend to get longer. It usually comes down to selecting from the available stock material sizes and lengths. Start with the prop. Then the shafting, then the motor. There are tons of motors, not so many good props for your ap.
the fact that the contest involves such wide power band doesn't help matters. Honestly, there are much more important things to fiddle with. Finding the best balance in the boat (trim) will be at least as important as shaft angle. If you end up at fifteen degrees, I wouldn't lose any sleep over it.

 

update

we have accquired a canoe and a trolling motor. We have designed our circuits and things are coming together. will send more when time permits.
k & J

 

need some advice

Our boat is coming together nicely,but we need some recommendations on mounting our motor. We are using a 16 foot canoe and have manufactured a motor housing that will mount our motor under the boat. Our question is where from front to back is the best place to mount the motor housing. Our prop must be inside the stern of the boat. Is there a perfered position to mount it? Your help would be appreciated.
Thanks,
Jennifer

 

Racing canoes & kayaks offer best speed if the bow is pitched down ~1 inch. In short, you're slightly bow heavy. Thus, you need to completely rig out your canoe, person and all, and load it until you optimize the bow position. Move your the seat & gear slightly forward until you achieve this slight bow heavy condition. Mark the bow with a black grease pencil on the outside if needed.

Once you have a well balanced, slightly bow heavy position achieved, mark the location of the motor, batteries, etc. and begin to permanently mount that equipment.

This slight bow heavy strategy also applies to most larger boats. It reduces the waterline length of the hull just a touch to give you optimum performance for the hull.

All this said, if you haven't taken these steps and your canoe is already stern heavy, you may not win the race. Stern heavy boats move less efficiently through the water.

Good luck!

Joseph

 

Motor location

Thanks for the input. We have mounted our steering assy , solar panels and control panel. So the cockpit, batteries and misc have not been mounted yet. So this is great input but how do we position the motor assy. The rudder is at the stern but we can mount the motor anywhere in front of this assy. as long as the prop is inside the stern. So do we position it for balance or is there postion that will optimize power and steering?
Thanks,
Jennifer

 

Mount seat & batteries forward as needed to achieve the slight bow dip I pointed out. As for the motor, without seeing a sketch or pic I couldn't say. It shouldn't be as heavy as the batteries, so perhaps ~18" to 24" forward of the stern. find a good spot that's accessible so you can do maintenance if needed.

Also, unless the trolling motor housing already has a weed/rock guard, I would also suggest mkinting one just forward of the prop.

Feel free to send a PM if you have additional questions or need a better explanation on balancing the load.

 

is it possible at this late stage to nix the rudder and go with a rotating azipod style motor mount ? would save resistance and overall weight, weight being a key factor in lowering resistance.

 

If you're using a trolling motor housing that might not be a bad idea for this particular race. As I recall part of the race included making tight turns. I would mount it about 24" to 36" aft of midship so you can nearly turn on a dime.

 

Pic of our solar boat

Here is our boat. We are in the process of mounting the motor, but would like to optimize the postion. Any comments please.
Thanks,
Jennifer

 

As much as I hate the idea of agreeing with Boston, I'm afraid I have to.

I'd replace the rudder with the motor.

Less weight, less wetted area (drag), and you just can't beat directable thrust for maneuvrability.

Failing that, you could consider mounting it on the bow, making it steerable of course.

 

Yep, I concur that rudder doesn't look good. I would mount the rolling motor directly on the back of this canoe.

Do the rules allow that?

If not, they should. There are many flat-back canoes with trolling motor mounts. You're essentially doing the same here, but providing solar vs. direct battery power.

e.g.



Now,turning on a dime with a motor & rudder mounted on the very aft end of the boat will not allow it to turn on a dime. If the rules are flexible on the location of the trolling motor & rudder, I would mount them at least 24" forward from the aftmost point on the hull. Granted the shaft may be between the steersman's legs, but it will pay off on turns. It also means you'll have to drill a hole through the hull and add a mounting bracket for the motor mount. At the end of the day it all depends on what our competitors are doing and whether or not you want to win the race.


Also, move the seat (every inch counts) as far forward as you can to properly balance the boat, paying close attention to keeping the weight (batteries, etc.) centered and balanced equally left/right.

 

mounting the motor

We are at a point that the motor assy which is a home made housing that houses a 250W 24vdc scooter motor (could not find a trolling motor that would meet this spec), either needs to be mounted aft of the stern so that the prop is inside the stern (but where?) or redesign the steering and mount the motor to the bottom of it and move it inside the boat. This part is getting difficult to figure out, so some good advice would be appreciated.
Ken & Jennifer

 

this is where your speed will come from ......aero prop 8x8 8x10 + aero spinner

 

Just behind that seat would be a good spot. Build a small box/well with high walls, gunwall height, that runs clear through to the water. Fiberglas it in and drop down your leg making it pivot 120 degrees.
Now take that finely crafted rudder off and reroute the steering cables to the motor.