3 blade or 4
 

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

?:head:

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

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...

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.

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

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.

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.

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

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

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.

That has been my experience as well...if your prop turns too many rpms at wot then your holeshot should be neck snapping.

first reply on iboats
Unless I missed it I didn't see a wot speed.A brief check of Yamaha performance bulletins
a 20 ft11" Polar Craft CC with a 115 using a 13 X 19 al prop 2500 lbs ran 38 mph @ 5850
0-20 5.25 seconds. (antiventilation) Plate is 1/4" above the bottom It seems his setup is right though perhaps check the height.
Does he trim down for hole shot?

soooo yeah what is the motor height and top speed is gonna be an important key in solving this issue.

whoops... double post

its my sons boat and i think he said 34mph,but he did tell me that when its about 3/4 of the way down the throttle and puts it all the way down he sees no differance in the speed. its a white prop that came with the boat, probably not a very good one but an all around prop, and it tachs out at 6400rpms, to high

I'm betting that the tach is reading wrong.

steelspike on iboats posted: "A 19" prop at 6300 makes about 50mph.@ 6% slip.
As I'm sure you have figured, not likely.
I suspect the tach."

I agree with him... I posted your last comment just now.

I suggest checking out the tach.... maybe obtain another for testing purposes.

so what im hereing is that the prop is the correct size and its the tack thats giving wrong reading, well i will serently look into that and i will get back to you and let you know what the outcome is thanks for all the help
this problem will get correccted for sure

we are not certain of anything yet but we feel that the logical next step is to verify rpm and gps speed.

My calculations came up with a lower pitch prop but that would raise rpm's..... The only thing we can say for sure is that your stated rpm, speed, pitch, and engine do not match up.... there's a skunk in there somewhere and we need to find him.

THEN we can recommend a prop for ya.

we are not certain of anything yet but we feel that the logical next step is to verify rpm and gps speed.

My calculations came up with a lower pitch prop but that would raise rpm's..... The only thing we can say for sure is that your stated rpm, speed, pitch, and engine do not match up.... there's a skunk in there somewhere and we need to find him.

THEN we can recommend a prop for ya.

I did the exact thing you are considering on my 18 and did not like it. I had a new 4 blade stainless given to me. I lost about 6mph top end with a little better whole shot. It went in the bow for a spare and my 3 blade Stilletto went back on the motor.