Re: Aussie needs prop advice.
Sales brochure for the 225 says 5000-5500 so your target (per the experts) should be 5500 or as close as you can get.<br /><br />Engine height gives you reduced drag but allows for prop ventilation (cavitation). The right prop and it is not a problem and the Laser II should take care of a lot of that as it is a high performance raked and cupped ss prop....but you might read Kenny's prop report, 1st entry in the prop section and go to the last section where he talks about the larger boats; heavier loads.<br /><br />Again, per the experts, to change prop types/manufacturers you would introduce a new unknown.<br /><br />I guess I have learned here that the first thing you would do would be to jack your engine up and and when you have all of that that you can stand (cavitation) back down one notch to stop it and then look at another Laser II.<br /><br />Just ran your numbers thru the prop calculator:<br /><br />Gear ratio 1.64:1<br />Pitch 19<br />Rpm 5400<br />Theoretical speed 65<br />Actual you say 53<br />That's 18% slip (Probably ok for a 22' boat)<br /><br />Assuming you jack up 1 or 2 inches and your top speed and rpm's go up you are doing the right thing. If you just blow out, you have to stay where you are.<br /><br />Assuming you don't, Then take your new rpm's, say they now have moved up to 5800. Then we assume the slip has been reduced by the reduced drag (going faster, less hull in the water, less lower unit to push thru the water) so I'm going to drop it to 15% then your new theoretical speed is 60 mph....pretty fast. <br /><br />Anyway, theoretically then to come back to your max WOT rpm's of 5500 you would have to prop up to a .....calculating.....22 in pitch. Not much change for the cost of a new prop. <br /><br />But anyway hopefully you get the idea. <br /><br />HTH,....but I ain't no expert.<br /><br />Mark
