Re: the Right Propeller?
Hi there, welcome to iboats Burnsy.<br /><br />Probably best to ask this question in the "prop forum".<br />But here goes.<br /><br />The prop needs to be selected so it will put your motor at the correct rpm's at full throttle. If you have a tach, this is fairly easy.<br /><br />Generally, a higher pitch prop will give you more speed but lower rpm.<br /><br />Conversely, a lower pitch prop will result in slightly lower speed but higher rpm, and more pulling power.<br /><br />1 inch difference is approximately 175 rpm difference.<br /><br />If you have a tach, what are your WOT (wide open throttle) rpm's ?<br /><br />If you do not have a tach, you can guess and get a prop with 2 inches less pitch. This will give you a bit more power to get on plane.<br /><br />Really best if you can get the current WOT rpm and use it as a baseline.<br /><br />I think the "target WOT rpm" for your motor is approx 5000 rpm.<br />If you know the WOT rpm, post them here, and we can make a recommendation.<br /><br />Here is an article from the "frequently asked questions" page:<br /><br />Wide Open Throttle RPM's - WOT, Why its important to know.<br /><br />When running your engine at WOT, if it is reaching, but not exceeding the recommended rpm range, the current set up is acceptable. By setup, I mean engine performance, prop, engine height ("x" dimension), trim setting, etc.<br /><br />WOT is used as a measure of how the whole package is working. If your engine is functioning properly, but not reaching recommended rpm, then something is putting too much stress or resistance on the engine. It could be a prop with too high a pitch.<br /><br />If your WOT rpm have been in recommended range, but now they have dropped 500-1000 rpm, you know to look for the cause, before it causes further damage. Perhaps its an ignition failure, a carb problem, low compression, 500 lbs of water in the bilge, etc.<br /><br />Outboards run best when the resistance, or load on the engine is limited to the point, that recommended rpm's can still be achieved at WOT. Any more load than that would "lug" the engine, lowering performance, and decreasing the life of the engine. Not enough load, and you would over rev the engine. <br /><br />The engine operates best when the load matches the engine. Your setup is how you match the load to the engine. On a car, you have a transmission that does this.
