3 or 4 Blade for Pontoon 40hp Mercury

wilsontowing

Cadet
Joined
Sep 19, 2009
Messages
29
Hello, I just got a new Pontoon boat and know slim to nothing about props.

I know now it’s not a speed demon but would like a few more mph and rpms.

2001 Mercury 40 hp 2 stroke. Pushing a 21’ all aluminum fishing barge toon.

its only pulling 14mph at 3900rpm. Sweet spot for motor is 4500-5500.

its currently fitted with a 4 blade Michigan Vortex, only miners I see are C06 and I measure it at 11”

i also have a 3 blade 10.25/14p prop that came with it.
both aluminum.

what one would raise my rpm and a little more top end.

Thanks in advance
 

wilsontowing

Cadet
Joined
Sep 19, 2009
Messages
29
Also that speed was during a test drive before I bought it. Loaded with about 1000pounds, tubes were a little messy but not bad as it was stored in water. I washed tubes but haven’t checked speed since I washed them.
 

NYBo

Admiral
Joined
Oct 23, 2008
Messages
7,107
If the motor is running properly and the tach is right, neither. You need something on the order of 9" pitch, most likely. I run this one and get around 18 MPH at 5100-5200 RPM.
 

wilsontowing

Cadet
Joined
Sep 19, 2009
Messages
29
I felt that these are both too big. Tach was New last year and idles about 800 and idles in gear about 1000. It was used on an inland lake with a lot of pontoon traffic and channels so maybe that’s why they did it so they have better response?
 

NYBo

Admiral
Joined
Oct 23, 2008
Messages
7,107
Response will be worse when over-propped. They probably jut had these hanging around, or they didn't know how to prop a boat properly.
 

NYBo

Admiral
Joined
Oct 23, 2008
Messages
7,107
No way I would use a 14" pitch prop. Are you sure of the pitch? Aluminum props are usually sized in odd numbers.
 

ahicks

Captain
Joined
Sep 16, 2013
Messages
3,957
The pitch is likely more relevant than small changes in the diameter. 8" pitch is getting pretty small....
 

wilsontowing

Cadet
Joined
Sep 19, 2009
Messages
29
Ok, correction on speed with the 4 blade. I downloaded a new speed app and checked with 2 phones. 12mph wot..

got the new 12.1/9 and put it in today. Took her out tonight and I’m at 14-15moh at 4800rpm. I even pulled an open bow out to open waters that was pushed up on a break wall in the bay.

There may may be some room for a different prop but I’m happy for now with the performance. And today we had 1-2’ swells
 
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