Joe wrote:
>
> 1. everyone talks about reduction gears and the like...
I'm running direct drive on a 5m 'half cabin cruiser' (not a sail boat :-)
> if you had a (and i don't know if my terminology is correct here) direct drive set up but placed a 2:1 ratio with the larger pulley or gear on the drive shaft it would seam like i could have the prop spinning twice as fast as the motor and achieve hull speed with out having to have the rpm's on the motor as high, therefore using less power from the battery bank? does this make sense or is my thinking flawed... remember I'm still trying to figure out this electric thing...
>
This is back to front. People are gearing down the motors to enable the
motor to run faster and possibly make the system more efficient.
(increase the voltage, the motor spins faster, but the current drops to
keep the power the same - lower current, lower 'I squared R' losses). A
slower prop is also more efficient than a faster prop.
I must note that while my boat works well with a direct drive motor -
it's also lighter and smaller than your average sail boat - I weighed my
boat and it's approx 750kg 'ready to run' (i.e. all the kit for a day
out on the water on board). My motor (a Perm 132 permanent magnet
brushed DC motor) has more than enough torque at low speed to turn my
prop and move the boat with out exceeding it's current rating. A bigger
heaver boat with a direct drive set-up might overload the motor.
I'm still running my original prop which was part of the 2 stroke 2
cylinder (direct drive) petrol engine kit that used to power the boat.
No comments:
Post a Comment