How much thrust needed for kayak ?

D

DeaninMilwaukee

1 mW
Joined
Jan 20, 2011
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My wife and I use some inexpensive 10 ft " sport " kayaks for some recreational boating and are looking for some power assist to extend our range on these slow kayaks.

A trolling type submerged motor would not be a good choice due to the shallow and log/weed infested areas we frequent, so we are looking at an air propeller assist instead. What I had in mind was to use one of the myriad of low cost quadcopter setups available from Hobby King. Mounting will be easy, mount the motor in a milk crate ( for safety ) and bungee the crate to the kayak.

My question is how much thrust do I really need? We are not looking to boat without padding, more like help to raise the average speed at the same effort we are already doing. There are lots of inexpensive setups in the 1/2 to 1 kg thrust range, but is that enough?

Thanks,
Dean
 
Have you thought about the noise level of an air jet? I think it could ruin the quiet nature of the kayak experience IMHO. Having the motor submerged would keep the noise minimal, especially at your suggested power assist. I've seen some pretty sleek motor designs here that keep things streamlined, which shouldn't get you thick into trouble.

ES traffic on anything boat related is sparse. There are numerous threads & builds to get ideas, but getting direct feedback from experienced members is a waiting game. I've a hunch there is another electric forum with higher boat traffic :?:
 
I see your point, but having some experience with rc stuff I know they aren't automatically loud, and can be surprisingly quiet.

It has a lot to do with using a large prop at lower rpm as opposed to a small one spinning fast. Also, it wouldn't be running all the time anyway, mostly to help with headwinds or going upstream.

The other point for me is that a submerged prop would be nothing but trouble where we go, broken and fouled props would be common and make it more trouble than they are worth.


Dean
 
Maybe you do some testing by towing the kayak with a tow line that has something like a fishing scale attached. It seems kinda' PITA but with a little experimentation, it might give you an idea of how many pounds it would take to pull (or push) your kayak.

Maybe a small paddle wheel. DIY for sure but it could be shallow and not foul as easy as a regular water prop.
 
submerged setup like rc boat.....with enough power to unfoul itself...... :mrgreen: i also like the paddle wheel idea, but i think the quadcoper idea isnot good
 
Stand on the shore and see if she can paddle away while you hold her back with a fishing scale.
 
Even better...I guess I like complicated solutions. :?
 
Eclectic said:
Even better...I guess I like complicated solutions. :?
Click to expand...

The idea was yours pal, I just executed it differently. The credit goes to you.
 
The towing with a fish scale would actually work pretty well I think, would measure actual force required to go a given speed which I could measure with my phones gps.

I know you guys are joking about a paddle wheel, but that could probably actually work without getting fowled up on underwater stuff. I wonder what sort of rpm it would need to turn to absorb say 100 watts on a 12" diam paddle?

Dean
 
Once you have an idea how big your paddle is, and what kind of movement makes what kind of thrust, then estimating the required paddle wheel will be much easier. I believe 4 times more paddle would be twice as fast, and such returns make paddle sizing quite flexible. Enough to just guess and get results
 
DeaninMilwaukee said:
I know you guys are joking about a paddle wheel, but that could probably actually work without getting fowled up on underwater stuff.
Click to expand...
I thought it might be a better idea than a standard prop. I could see issues with where to put it. Any where around the cockpit and it would interfere with your paddling. Any where else and it is difficult to deploy. I could also see it causing aerodynamic problems when it is out of the water. A side wheeler could be being pretty tall if you had to keep a single axle above the top of the hull.
 
It would actually make more sense for a kayak paddle wheeler to have just one and to put it on the back, like an outboard motor.

It could then be steerable as well, with a pivot that would allow it to pop up if it hits something, or be tipped completely out when I don't need assist.

Now if I only had a clue what rpm the paddle wheel needed to be at so I could figure out how much gear reduction I need.
 
How fast do you paddle? say 5kmh. 5000 meters per hour. 85 meters per min. Your wheel is how big? Your trying to have a paddles worth in the water. A 50cm wheel might do. That is about 1.5m circumference. So at about 60rpm your sending 90 meters of paddle through the water per minute.


Just having my first brew of the day. That will need another look.
 
While you are out testing to find out how much it takes to pull your kayak around, maybe you could do some test paddling. Do some quick short strokes trying to emulate a paddle wheel cadence. Counting your paddle strokes should give you a handle on where to start with the paddle wheel rpm. Paying attention to how much of the blade you put in the water should give you a ballpark idea of how big you would need to make the paddle wheel blades.
 
I can't resist. Get one of these "Redneck Trolling Motor"
http://www.ebay.com/itm/REDNECK-TROLLING-MOTOR-4-KAYAK-TUBE-GATER-HUNTIN-FLYFISH-BOAT-CANOE-PONTOON-bass-/181650143444
$_35[1].JPG
It's just a prop on a long shaft that you hook up to a cordless drill. You could mount it like one of those long-tailed outboard river boat motors.
 
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