Propeller size

[toms4w]

I have a '95 3.0 L OMC cobra in a 17.5 ft boat and new to boating. Manual calls for 14.5x19 prop as standard, came used with 15x17 prop on. Manual WOT calls for 4,200-4,600 rpm, with the 15x17 I can get to 4,000-4,200. Also barely gets 1 average skier (2 skis) out of the water (with 2 adults in boat). Engine was previously rebuilt before purchasing. Isn't the 15x17 prop better than 14.5x19 for hole shot and getting a skier up? Since I can barely get a skier up I'm thinking I should change to maybe 15 pitch, but that is getting pretty far from the 14.5x19 prop the boat is supposed to have. Maybe it lost some power with rebuild? Would any of you experienced boaters recommend going to maybe a 15 pitch or staying put? Also, is there much difference in 14.5 vs 15 diameter? Thanks!

 

[WillyBWright]

Re: Propeller size

It isn't carved in granite that you HAVE to go full throttle. Watch the tach and adjust accordingly with a 15. Diameter doesn't have nearly as much effect as pitch. But it can mean more blade area for better (or worse) bite. Elevation has a significant effect on what prop you use. Where are you?

 

[ron7000]

Re: Propeller size

Find out the outdrive gear ratio, should be near 2:1. If it's lower, like around 1.5:1 then going to a smaller pitch prop (because it's turning more rpm per engine rpm) is ok to do. Otherwise you either have an engine problem, or a hull drag problem.<br />I recently pulled my 19' out of the water, after the torrential rain we had the hull, drive, and prop was loaded with barnacles. Boat wouldn't get over 30mph and 3500rpm. Usually does 45mph at 4800rpm no problem. For comparison, I have a 19' bayliner, 2002, 3L merc 130hp, 1.98:1 drive with a 14x21 3-blade prop. It's a little rough getting up on 1 ski, 2 skis no problem at all.

 

[QC]

Re: Propeller size

You sure the tach is right? If so, I'd definitely go with the 15. Engine should not have lost power, but the boat may have gained a little weight. Soaked foam etc. <br /><br />You might try this on the prop forum. You'll get more attention over there.

 

[toms4w]

Re: Propeller size

Appreciate the responses. To answer some of your questions:<br />-elevation is 1600, so I wouldn't think it is an issue.<br />-don't know the outdrive gear ratio, will need to look into that.<br />-the hull is clean, so drag shouldn't be an issue.<br />-just assuming tach is correct, need to check.<br />As suggested, I'll post on the prop forum.<br />Thanks.