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Trolling Motor Props

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Has anyone experimented with different props for better speed or efficiency?  I ask because I have a canoe for getting onto lakes without ramps.  Some of them are still pretty big.   I think most trolling motor props are designed for heavier bass boats.  With a light weight canoe are there any benefits to changing props?  

15ft Canoe with 2 men, batteries, gear is only 650 lbs.  Currently using Endura 30# and getting 3 to 4 mph depending on tail wind.

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I have been playing around with props on my MK40 for a while. My boat is a kayak kit that should be very similar to your canoe. Here is what I have found.

Most props on trolling motors are designed to provide max thrust and not much speed. They have a pitch of 4 inches (they move 4 inches thru the water for each revolution) and are very effecient for this purpose. The motor driving the prop is a constant rpm / volt motor. All I have tested are 150 rpm per volt. So with 10 volts on the motor it spins 1500 rpm, and with 12 volts its 1800. It doesn't matter if the prop is in the water or out of the water, it always spins at 150 prm/volt. Trolling motors are rated in lbs of thrust (when the boat is not moving) and draw about 1 amp per pound of thrust.  30 lbs of thrust sounds much better than 1/2 HP and it will draw 30 amps when generating it rated thrust.

Kipawa offers an aftermarket 3 bladed prop that looks attractive. I called them and could not find anyone that knew what the pitch or diameter of their prop is. So it is hard to estimate if it is right for me. I think they wanted about 45 bucks for their product.

I now run a Nissan 3 blad prop from their 3 hp O/B. It has a pitch of 7 inches and at 7 1/2 inches is about the right diameter. With this prop, at full throttle my motor draws 28 amps (yours is rated for 30amps) and the boat speed is 4.3 mph. My objective is to have the motor drawing its rated current (40 amps) at full throttle on my boat. So it is not quite big enough for my motor, but is about right for yours. At 3 mph this prop draws 25% less current than the stock prop, so it extends my run time if I don't get in a hurry.

Incidentally I have tested this and other props on a 28, 40 and 50 lb motor and all provide the same top speed, because they are all turning the same rpm. Also all draw the same battery current, because they are all doing the same amount of work. The upper limit is set by the current rating of the motor. So the 50 lb motor could swing a larger prop safely, but offers no advantage over the 30 lb motor with this particular prop.

The down side is the tohatsu prop has a 1/2 inch shaft size and the MK shaft is 3/8ths. So a bushing is required to make it fit. Aslo the tohatsu motor doesn't have a prop nut (it uses a pin to retain the prop), so the prop must be machined to provide a recess for the MK prop nut. The tohatsu p/n is 3FO641010M. These can be found on line. I made my first one using a hand drill and don't recommend it. It is hard to get everything perfectly centered and an off center prop will cause the motor to vibrate. So if you are good with tools and have a drill press, you might make this work for you. Good luck ;)

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Thanks sneaker.  i went back and reread some of your older posts on this topic.  It appears I have a theoretical hull speed of 5.96 mph.  So I have some work to do.  I se no reason to go only 3 to 4 when 5.5 should be fairly easy if I find the right set up.  I have ordered a 55lb and will try it first since it should have a bigger prop.  Then on to some more pitched props.

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