I have a very tiny, ancient trolling motor on a 14-foot fishing boat that weighs about 350 pounds and has an extra 200 pounds of permenant gear on board (outboard motor, battery, and two anchors). I think the thrust is only 12 pounds, but it will power the boat into any wind, just not real fast. It's nearly as strong as a person powering the oars. I once used a motor with 30-pounds of thrust on a little Jon boat overloaded with two people on board, and the motor had a whole lot more thrust than one strong rower, and pushed the Jon boat faster than hull speed. Thus I think the smaller or those two motors will be more than adequate on your canoe.
Hull resistance Well, for a 14’ kayak, drag at hull speed will be in the general range of 5 to 10 pounds. You can deduce this by looking at a few Sea Kayaker boat reviews. A canoe shouldn’t be much different, so I’d say the smaller motor will do fine.
Of course, we have no way of knowing whether the thrust values quoted by the mfg have any relation to reality. But given that 45 lbs thrust is so far over the needed value, I’d guess it should be more than adequate.
Speed difference? thanks the canoe weighs 45lbs so the 45lb should be plenty. There would not be any speed difference as it couldn’t break hull speed? Just winding what others get for speed with their electrics
Speed Yes, you can surpass hull speed, you then transition to the planing regime. I think you can aid the process by trimming the stern heavy to allow the bow to pop up.
It’s worth considering that trolling motors and their propellers are designed for low speed, e.g. a couple of knots. If you’re going much faster than that, the propeller isn’t really designed for it. It will go, just not be as efficient. There is a kayak motor called the Torqeedo that is designed for faster speeds - it has a smaller, higher pitch propeller to send the boat around 4 or 5 knots, I believe. I’d like one to play with, but they’re surprisingly expensive.
First, I don't think any of the regular posters here ever use electric motors, so I doubt that anyone can answer your question about how fast your motor will be.
As far as the bigger motor being faster, yes, it will be faster. However, it won't get you planing like a speedboat. Instead, I expect that the speed will be in that "wallow in the hole" zone that's faster than hull speed but slower than planing efficiently. I once read about a fuel-economy experiment that someone did with a gas outboard motor on a small fishing boat. By far the best fuel economy was gotten at the lower end of the slow-no-wake speed, and by far the worst fuel economy was at "wallow-in-the-hole" speed with the bow high and the stern sunk deep (for those that wonder, the most efficient cruising speed was "just" fast enough to be planing cleanly). If it were me, I don't think I would want to waste battery power trying to go just a little bit faster while traveling at a speed that's already making the least-efficient use of "fuel". Perhaps the larger motor will run more efficiently at slow speeds than the smaller motor, but I only say that as a way of pointing out that I have no idea which motor will run longer when used "wisely". Still, my hunch is that the smaller motor is the better choice.
My 35# thrust electric motor powers my 15' canoe about 4 mph, which is good considering the hull speed of a canoe is not over that (additional input of energy over 4 mph has diminishing returns). A larger motor will go through your battery too fast. I can power the canoe for one hour at 4 mph with the 35# thrust motor. Mostly I use it to extend our range and get to the more interesting paddling areas more quickly, and then we paddle like normal after I stow the motor.
Good thing someone thought of the floatation issue. Many canoes only have enough floatation to float themselves, and in most cases that's okay because gear packs float too. A battery on the other hand, really could sink the boat after swamping or capsizing (and the motor isn't all that light either)
Here's another issue to think about. Local boating regulations will almost certainly require the battery to be securely fastened to the boat so it can't slide around or tip over. The battery will also need to be enclosed so that cable connections are not exposed. The original poster might already know this, but no one wants to get a ticket for rule violations.