prop selection

mattttt25 · Nov 14, 2002

original post deleted by steve... 1997 sunbird neptune 200cc (approx 2200lbs) 1998 johnson 150hp oceanrunner great acceleration and top end. but at wot my rpm's were only 4600, and based on other posts, it sounds like the wrong prop. suggestions on best prop to maintain good acceleration and top end? i know i sacrifice one for the other, but how about a good compromise? are there charts or other sources for this info? thanks-

janichol · Nov 14, 2002

Re: prop selection

Matt, Although not an expert, I have found out that just WOT isn't the only indication of how well the boat as a system is running. I thought I was underprop'd until I got everything running right, put in a working tach and ran it. TRIMMED at WOT is now 5600 rpm, 44 mph (21 ft Aquasport w/200 Johnson, 3300 lbs). If I trim down forcing the bow into the water, I'll lose about 800 rpm. I also replaced the mini wing on the cavitation plate with a better (more aquadynamic one)and can get on plane faster. First thing to do though is find out what size prop you've got (mine is 14 1/4 x 17 SS)

mattttt25 · Nov 14, 2002

Re: prop selection

yes, i need to figure out the current size. i was on smooth water and trimmed up to maximize rpm's and still ran at 4600. i asked before if it could be the tach or throttle and i was told by the experts it was the prop size. would hate to buy different props just to figure this out. thanks-

wilde1j · Nov 14, 2002

Re: prop selection

That motor should turn ~ 5800 WOT. You probably need 5 to 6" less pitch if motor is at max power.

Dhadley · Nov 14, 2002

Re: prop selection

Make sure its an OMC tach and then look at the back of it and make sure its set on position 6. If the tach never changes from trim down to trim up, I'll bet its the tach. Have a dealer run it with a shop tach just to verify accuracy. Good luck!

rickdb1boat · Nov 14, 2002

Re: prop selection

15" X 17" Prop should be right or at least close.

janichol · Nov 15, 2002

Re: prop selection

Hey Rick, I'm going to pick up a spare prop... If I'm running a 14 1/4 x 17, would a 15 x 17 be a good choice? I'm assuming the larger diameter would reduce RPMs but possibly increase speed. Correct? Thanks,

rickdb1boat · Nov 15, 2002

Re: prop selection

It would be comparable to what you have, although you may pick up a couple of MPH with the larger Diameter! Good Luck,

rickdb1boat · Nov 15, 2002

Re: prop selection

Did you figure out the RPM problem?

mattttt25 · Nov 15, 2002

Re: prop selection

unfortunately the boat has been winterized and i won't be changing props until spring. just wanted to see what sizes i should be looking for. thanks-

radsrh · Nov 15, 2002

Re: prop selection

From the information I have, increasing the pitch 1" will lower the RPM 150-200 and reducing the pitch by 1" will increase 150-200 going from a three blade to a four blade will reduce the RPM by 50-100 RPM at WOT. If you want to test your boat with different props before buying go to the Mercury Marine web site and find a dealer in your area that has demo props, you can use a Merc prop on your Johnson with there hub kit that way you can demo different pitches on your boat to find the best WOT and Hole Shot you are looking for before you put your money down. There site also has a feture called prop selector where you can input your boat weight, HP select your gear ratio primary use ect. and it will guide you in the right starting direction

prop selection

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