I am running 540 motor in my boat and it heats up real fast. Is there a way to solve the issue like gearing etc? How much should I gear down?

If you gear it down it'll mean that prop will turn slower, will do less work, but let the motor do it easier/cooler. You could do the same thing by using a finer pitched prop. Same prop rpm as without the gearing, but less water being moved by each revolution. Or, keep the same pitch as now and reduce the props diameter. Just a few methods of doing the same thing, some less expensive than others. Then again, it depends on what the boat's purpose and hull type are. A reduction in prop speed, or water moved each revolution of the prop is sort of counter productive for a 'go fast' boat, not so bad for a slower one... sort of.
Water cooling the motor is another solution, depending on just how hot the motor gets. Would you like to narrow the playing field a bit and tell us what kind of boat you have so we can make more guesses?
- 'Doc

My extensive discussion on gearing is [link=http://www.rcgroups.com/forums/showthread.php?t=700329]here.[/link]

Depending on where you are starting, a geared motor MAY run the prop at about the same speed... because the prop is lugging down your too-small direct-drive motor, which causes it to pull more amps and get hot. The same motor will speed up with the gearing, somewhat counteracting the gear reduction... but it will pull fewer amps. Like magic!

Easy things first - does the prop shaft spin freely? A tight shaft is very good at making a motor work too hard and heat up.
A fairly useful rule of thumb I was given was that the prop should be of a smaller diameter than the motor.
Any gearing then makes the motor think it has a smaller prop to drive.

It's the midwest boothbay lobster boat which I diy myself. I am running 540 motor on it and after 1 pack of batt, the motor really heats up. I am considering gearing it down but not sure where to find the gearbox for 540 motors? Really appreciate the great advice rendered.[sm=thumbs_up.gif]

Judging by other building and running threads, your boat, in combination with the right prop should ba able to run about an hour on one charge.

What prop are you using and what motor (as there are several types og 540 motors).

If you're going to gear down, I'd advice a belt reduction as used in electric flight, very smooth and virtually noiseless (as opposed to many gearboxes).

Regards, Jan.