3 blade or 4

steplift20 · #1 02-18-2012, 05:34 PM

i am curently turningto go with a 4 blade a 13x19 in prop on my 19 foot polar and want put on a 4 blade 13x19 inch the question is whtshould i expect in the diferance of performance
thanks

spareparts · #2 02-18-2012, 05:37 PM

?

reelapeelin · #3 02-18-2012, 06:19 PM

Quote:

Originally Posted by spareparts

?

...might consider a re-do on that one..

If yer considering going from a 3 blade prop to a 4 blade of the same P & D, you may not notice much difference except a couple of MPHs off the top...generally 4 bladers are considered "stern-lifting" props, so it might get the bow down a bit...

smokeonthewater · #4 02-18-2012, 08:30 PM

Quote:

Originally Posted by steplift20

i am curently turningto go with a 4 blade a 13x19 in prop on my 19 foot polar and want put on a 4 blade 13x19 inch the question is whtshould i expect in the diferance of performance
thanks

yep, pretty sure those props will perform the same lol

now from 3 blade to 4 is another thing.... what rpm are you running at wot with a normal load now?

Generally going from 3 to 4 blade warrants a drop in pitch to maintain rpm and OFTEN you lose a few mph.

steplift20 · #5 02-19-2012, 02:23 PM

its a 115 yamaha 4 stroke and wot is 6300 it should be 5700 plus its hard to get her to plane, im not looking to go faster just lower the rpms and bring the bow down faster. i think the biggest diameter is 14 that i can go, sorry about the original post , i guess i left out a few things

Genie Aye · #6 02-19-2012, 04:36 PM

You will loose RPM for sure by staying the same on dia and pitch. The question is how it will pull out of the hole??

You will have to let us know---theory is it will pull out better, but if it is to much load--you know what will happen--

This is the prop change question we all have for sure.

smokeonthewater · #7 02-19-2012, 10:41 PM

I borrowed the following from another forum I frequent:

"ESSENTIAL DATA REQUIRED
When posting a question about propellers, you cannot get a reasonable answer unless you provide the following information in your post: Items 1-4 are essential for meaningful response to most questions.
1) Performance issue you are trying to correct.
2) Current prop manufacturer, model, aluminum or stainless as a minimum.
3) Current prop diameter and pitch (required).
4) Wide open throttle RPM and speed with an average load (very helpful)
5) Engine/drive make, model, year, and HP
6) Boat make model, year, length and weight"

(posted by JB on Iboats.com)

With this data we can figure you prop quite accurately.

steplift20 · #8 02-21-2012, 08:14 PM

response to most questions.
1) Performance issue you are trying to correct.--- get on plane faster and lower rpms to with in range 5800
2) Current prop manufacturer, model, aluminum or stainless as a minimum.--- aluminum, 13x19 its the prop that came with the engine
3) Current prop diameter and pitch (required)---. 13x19
4) Wide open throttle RPM and speed with an average load (very helpful) ---6400 rpms
5) Engine/drive make, model, year, and HP--- yamaha 4 stroke 2003 115hp OB
6) Boat make model, year, length and weight"--- 19 foot polar 2003 about 2000lbs center console

smokeonthewater · #9 02-21-2012, 10:24 PM

Got the fellas on iboats workin on it... I have a couple ideas but waiting to see what they think.

smokeonthewater · #10 02-21-2012, 11:25 PM

are you certain that your tach is correct? I have been running some prop calculators and am coming up with a lot lower pitch than you have now.
what is your current top speed?

any chance that your hub is slipping or that your prop is ventilating?

Such a high wot rpm should go hand and hand with a dynamite holeshot.