will changing from prop 15x19 to 14.5x25 be better? 3 blade to 4?

letsbarbq

Petty Officer 1st Class
Joined
Jan 6, 2002
Messages
241
Hello to all. got a long shaft oceanrunner 225 on a big boat. its a wellcraft 25 foot walk around.<br /><br />my goal. --- 1 rpm = 1mph.<br />Lowest RPM, fuel effient, never WOT, 20-30 mph. I dont care about holeshot or fast. Just need to conserve gas tank for long offshore fishing trip.<br /><br />what i got now stainless 3 blade 15x19 cupped little. WOT can be above 5900. rpm is 4000 and i get about 25 mph.<br /><br />Will the rpm be lower and my speed pick up if I goto a 14.5 x 26 pitch? <br /><br />What about if I change to a 4 blade prop with hig pitch. what kind of performance do i get? i read some posting about 4 blade and it has made me confused?<br /><br />any help would be appreciated.
 
D

DJ

Guest
Re: will changing from prop 15x19 to 14.5x25 be better? 3 blade to 4?

BBQ,<br /><br />Long time, no here from. If you're the same person?<br /><br />You're winding that engine up about right (5900).<br /><br />A four blade will, definetely, get you out of the hole quicker and will hold on better in turns.<br /><br />If you're running a 19" pitch now, you can probably do the same with a four blade. You'll lose a few RPM's, but you're in the RPM range.<br /><br />Dhadley will come along, soon, and make me look like an idiot.
 

WillyBWright

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Dec 29, 2003
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Re: will changing from prop 15x19 to 14.5x25 be better? 3 blade to 4?

26 is probably way too steep. You'll probably drop to under 5000 if you can even get out of the hole. I can see one on a light bassboat, but not a 25 footer.
 

Dhadley

Supreme Mariner
Joined
Feb 4, 2001
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16,978
Re: will changing from prop 15x19 to 14.5x25 be better? 3 blade to 4?

The guys are right. A 25 will kill everything. Holeshot, top end, mpg and eventually the motor.<br /><br />5900 is perfect for that motor with an average load. The thing now is to concentrate on set up. Yes, a 4 blade should help. But it will run at a higher X dimension. That reduces drag which helps increase efficiency. <br /><br />For some reason your numbers for cruise sound off a bit. 4000 rpm with a 19 should be way more than 25 mph. Now, when you say "WOT can be above 5900" what do you mean? How far above 5900?<br /><br />Whats your top (accurate) speed? At 15% slip you should be in the upper 40's.<br /><br />BTW DJ -- I have a feeling nobody could make you look like an idiot....
 

Dhadley

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Feb 4, 2001
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Re: will changing from prop 15x19 to 14.5x25 be better? 3 blade to 4?

Hold on a minute... just read your other post<br />
its gonna be be on a wellcraft 25 foot walk around.
Have you run this motor on the boat or not?
 

letsbarbq

Petty Officer 1st Class
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Jan 6, 2002
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241
Re: will changing from prop 15x19 to 14.5x25 be better? 3 blade to 4?

hey, yes its the same ole me. Got married and had 2 kids since last posting. <br /><br />so it sounds like a 4 blade, smaller diameter 23 pitch? might help?<br /><br />yeah, i can rev it to bout 6300 rpm, isnt that high?<br /><br />sorry, mistype. it is on boat. and rpm at 4000 cruise the boat at only 25 mphs.<br /><br />would a smaller prop. higher pitch help? or is the boat just to big for a johnson 225. i am hoping i haven't prop correctly thats all.
 

letsbarbq

Petty Officer 1st Class
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Re: will changing from prop 15x19 to 14.5x25 be better? 3 blade to 4?

o yeah, glad to see that the website and all familiar names are still around.
 

walleyehed

Admiral
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Jun 29, 2003
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6,767
Re: will changing from prop 15x19 to 14.5x25 be better? 3 blade to 4?

You need to stay with a larger diameter prop with the load you have. It's not going to be a speed boat regardless.<br />See what Dhadley thinks, but I think a large, high efficiency 4-blade in a 21 pitch will be a good choice
 

letsbarbq

Petty Officer 1st Class
Joined
Jan 6, 2002
Messages
241
Re: will changing from prop 15x19 to 14.5x25 be better? 3 blade to 4?

I dont want a speed machine. i'm on a offshore boat and most of the time we barely get a nice calm day on the seas so cruising 15-20mph is consider a good day. i just want to lower my rpm at cruising speed. I just want to cruise about 3000 to 3300 rpm and cruise about 25+ mph. <br /><br />would a 14.5 by 21 pitch 4 blade do better?
 

walleyehed

Admiral
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Jun 29, 2003
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6,767
Re: will changing from prop 15x19 to 14.5x25 be better? 3 blade to 4?

That would be a good starting point, but please understand you must still prop for 5800-5900 max. your cruise will likely be closer to 3500-3700 for max efficiency, but again, this only works if proped for the high-end RPM.<br />If you over-prop, the throttle plates are wide open at your lower RPM, which equals pi$$-poor fuel economy.
 

fireman57

Captain
Joined
Aug 24, 2004
Messages
3,811
Re: will changing from prop 15x19 to 14.5x25 be better? 3 blade to 4?

Married, 2 kids, and still have a boat much less time to use it? You're doing something right.
 

letsbarbq

Petty Officer 1st Class
Joined
Jan 6, 2002
Messages
241
Re: will changing from prop 15x19 to 14.5x25 be better? 3 blade to 4?

hey fireman57 --<br />its alot easier when you get them involved<br />you're right, i need to go home and thank her
 
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