got a prop problem. what size do I need for a yamaha 250?

[letsbarbq]

Was wondering if anyone can help me with any information. Because I am clueless.<br /><br />I have a 23 foot walk around. I have a yamaha 250 hp outboard. When motor is fully trimmed down. I can only get about 3400 RPM and the steering is very hard -- it breaks to the right just as soon as I let go. I feel like I am fighting th steering all the time. Now if I slowly trim the motor up while I am running, I noticed the rpm going higher and the speed picking up and the steering easier to control. Can anyone tell me if this is because the prop is not right for my set up? <br /><br />I want to add that from a stand still, I push the control down and the rpm will slowly go up then slowly accelerate ---- this is not instant, it takes the rpm awhile to go up. is this the prop pitch? anyone know what prop pitch or size is factory for this motor? And anyone know how I can tell what I have now? any help would be appreciated. Thank you ahead of time.

 

[Forktail]

Re: got a prop problem. what size do I need for a yamaha 250?

That motor should run between 4500-5500 rpm at wide open throttle (WOT).<br /><br />Your prop will not have much to do with the steering issue you mention. This is a common problem on boats called torque steer. It is a result of the direciton the propeller is turning which causes a torque in one particular direction (same affect and reason why helicopters have a tail rotor). Hydraulic steering rather than cable or rack steering will help considerably. There is also a little trim on the cavitation plate that you can adjust to compensate somewhat.<br /><br />When you instantaneously push the throttle to wide open, the engine will not reach maximum rpm instantly. The outboard does not have a variable transmission or a variable pitch prop, so the the prop is a compromise for speed and power combined.<br /><br />There is really no particular prop pitch size for that outboard. They do not come from the factory with a particular prop installed. The dealer usually installs a prop which is selected from a series of props sized to fit your boat applicaiton. The dealer's experience comes into play here. The diameter X pitch should be stamped on your current propeller.<br /><br />When your boat is fully trimmed and running at WOT and maximum speed, your outboard should be turning between 4500 and 5500 rpm. If you are unable to get 4500 rpm then you need a smaller pitch prop. If you are above 5500 (without cavitating) then you need a lager pitch prop. So go by the rpm.<br /><br />A smaller pitch prop will help with accelleration from a stand still. And a larger pitch prop will increase top speed. A compromise between the two for your rpm is the best.<br /><br />Most props for that outboard and your application will come in a 17, 19, or 21" pitch.

 

[letsbarbq]

Re: got a prop problem. what size do I need for a yamaha 250?

thanks forktail, that help clear up alot. I'll get to that and let you know what pitch I have tomorrow.