Too much prop?

Message

beermunk · #1 Post by **beermunk** » Fri Mar 20, 2009 7:19 am

I've done some reading up on this and wanted to get ya'lls opinion. Our new boat with the Mercruiser 3.0 Alpha One came with a 15x15.5 three blade prop on it. When we took it out WOT was about 4200rpm. From what I have been reading, that seems like a bit low in the RPM department for this motor. What are your thoughts?

Seems like people are getting a better top speed with a 14x13 prop on longer pontoons. Also does anyone have any experience from going from three to four blade? I've read what the differences are supposed to be but I was wondering about actual experience.

FloterBoter · #2 Post by **FloterBoter** » Fri Mar 20, 2009 12:06 pm

I'll give you what I experienced, but our boats are different enough that it may not help.

28 foot Harris with two logs, not three like yours.
Mercruiser 140 I/O

The boat had a four blade prop on it, I think it was a 13" pitch. It blew out around 3500 rpm
or even lower. Wouldn't hold bite at all in turns. Tried various three blade props. One 16" or
17" pitch prop was pretty amazing for top speed, but getting started was mushy and it would
lose bite in wavy conditions. My current prop is a 15-1/4" dia x 15" pitch three blade. Works
very well. Good starting (wouldn't really call it a hole shot...), good top end, holds well
in rough water. Every once in a while it loses bite on sharp turns in rough water or even
straight ahead in really rough water--so then you have to be ready to pull back the throttle
ASAP or it'll go above redline.

Look at that, I even typed this with capitalization. Better go check my temperature..............

beermunk · #3 Post by **beermunk** » Fri Mar 20, 2009 12:19 pm

Sounds like I may have to wait until I can get a new prop on to find out. I may already have the correct one... hmmm

firebob · #4 Post by **firebob** » Fri Mar 20, 2009 1:17 pm

Your motor has a WOT range, your prop should allow you to run that range. It's a trial and error type of thing. Most dealer have props that they will let you try out.

WaltF · #5 Post by **WaltF** » Sat Mar 21, 2009 1:24 am

wot for the 3.0 is 4400-4800.
with just a couple people in mine, i can just reach 4400.
im running a 3 blade aluminum 16x14.
id like to try a 15x13 or so this summer to see what happens...

beermunk · #6 Post by **beermunk** » Sat Mar 21, 2009 6:05 am

WaltF wrote:wot for the 3.0 is 4400-4800.
with just a couple people in mine, i can just reach 4400.
im running a 3 blade aluminum 16x14.
id like to try a 15x13 or so this summer to see what happens...

Do RPMS's go up or down with more weight in the boat? I noticed our 4200rpm WOT with three adults and a child in the boat. That's about half the normal weight we'll probably be hauling.

WaltF · #7 Post by **WaltF** » Sun Mar 22, 2009 9:17 am

Do RPMS's go up or down with more weight in the boat?

Yup! They sure do.
I can reach 4400 with only 3 in the toon.
Once i have like 12, its crawling.... like may reach 3800 ish...

I usually just set it at like 3300 when im that full n putt around...

BUT HEY!! having all those friends is most of the fun!

mikeherb · #8 Post by **mikeherb** » Sun Mar 22, 2009 10:01 am

RPM's also go up and down with the change in pitch. More pitch = less RPM's at WOT.

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