Torque vs speed

[woodsailboat]

I have a 40 lb thrust Motor Guide trolling motor that has a three blade prop that will push my 14 ft jon boat at about 5 knots, I also have a 27 lb thrust Minn Kota trolling motor that has a two blade prop that will push my boat at about 4 knots and my question is, does the amount of blades determine speed vs torque like a transmision.

 

[steelespike]

Re: Torque vs speed

Torque is almost never discussed except when comparing same hp motors of different displacement.
It is generally felt that the larger displacement motor will have better hole shot/pulling power due to its higher torque.
Thats about as detailed as it gets.
A 3 blade prop should have better control and probably acceleration. it is harder to turn that a 2 blade.
Being easier to turn and said to be more efficient may be why 2 blades usually appear on a smaller motor.
I think a 3 blade on your 27 set up to run at the same max amperage would produce about the same speed maybe less because of the additional drag
from the additional blade.
2 blades usually don't do as well pushing a load.Your 40 has almost 50% more power to produce about 25% more speed.
I think trolling motors are designed to provide good control and produce long operation so they are designed to run at a power saving rpm.So I believe a tinkerer with a long slender displacement type boat could tinker with a trolling motor to produce higher speed
but at a higher amperage.