Prop Help 4.3 Merc

ttrip

Recruit
Joined
Jun 4, 2019
Messages
3
Hello! I'm looking for some guidance on a new prop for my old mans boat. It's a 19' Maxum (approx 2400#) with a fresh rebuilt 4 bbl 4.3 Merc and a 1.84 ratio Alpha One. It currently has a 4 blade 17 pitch Trophy Plus Stainless prop. The boat runs good but over revs, going 39 MPH at 5300 RPM. This works out to about 16% slip. I'm thinking that going to a 19P 4 blade should get it back into it's power band, but any advice would be appreciated.
 
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porscheguy

Chief Petty Officer
Joined
Jan 17, 2013
Messages
441
I run 21p props on my 19’ wellcraft with a 4.3 2barrel and the same gear ratio as you.
 

Sea Rider

Supreme Mariner
Joined
Sep 20, 2008
Messages
12,345
Welcome to Iboats,

What's the min-max wot rpm range factory stated for that motor ? You like boating lightly, medium light or fully loaded ? Load if extreme is a natural wot rpm killer.

Happy Boating
 

ttrip

Recruit
Joined
Jun 4, 2019
Messages
3
The WOT range is 4400-4800. The boat might see 4 adults on occasion, but is typically loaded less than that. The boat is definitely under propped right now
 

Watermann

Starmada Splash of the Year 2014
Joined
Jan 12, 2013
Messages
13,747
Yeah I agree that 17p is way too low, a 19p SS 4 blade should drop your RPMs by around 4-500 which would get you right at max RPMs.
 

ttrip

Recruit
Joined
Jun 4, 2019
Messages
3
I think we'll go with a 19P Quicksilver Nemesis and see how that goes. Thanks for the replies!
 

TunaFish389

Petty Officer 2nd Class
Joined
Apr 26, 2018
Messages
184
I would try a 21p three blade. You will loss about 700rpms and your slip will go down compared to the four blade.
 

Sea Rider

Supreme Mariner
Joined
Sep 20, 2008
Messages
12,345
If like 4 blades props try same 4 blade with 19 pitch, definitely will lower wot rpm a lot but only a wot run on flat calm water cond will determine so. It isn't know if going 3+ pitches will render -700 wot revs as the rule of thumb not always works spot on all combos will depend entirely if being, light, medium light or heavy ones.

Happy Boating
 
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QBhoy

Fleet Admiral
Joined
Mar 10, 2016
Messages
8,286
I’d be at a 21” 3 blade good quality stainless like a enertia, mirage + or laser 2, for sure. I’d have a 23” for cruising and too end too, haha.
 
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