right prop size-help

[mhope01]

I have a 1990 115hp merc
Currently has a 3 blade aluminum prop, I can't tell what size because the paint is covering it over.

The 17ft proline I have it on is turning 5600 at WOT and runs around 39-40mph on the speedo.

What size prop should this motor have and I thought the spec WOT rpm was supposed to be 5250?

 

[croSSed]

Re: right prop size-help

This should really be in the prop forum, but, be that as it may...

There's no way to really tell what prop you SHOULD have without first determining what prop you DO have. It's "probably" anything between a 17 P to 20 P. Take it to your local prop repair shop and have them look at it. They could find out what pitch it is by simply dropping it in a pitch block or two. Now, having said that...

How often do you run your engine @ WOT? If you are like most people and only run it that high in short bursts, my own feeling is that 5600 is not a problem. How does your boat perform? Does it have good overall performance? Does it come out of the hole pretty hard? If you like the way it performs over all, I'd say leave it alone. If you go up one more pitch size (whatever pitch that is) you are going to give up low end and midrange acceleration. You "might" gain a mph at top end - maybe 2. Just my 2 cents.

TG

 

[Scaaty]

Re: right prop size-help

Your fine..5600 is spot on good'nuff. I think you are confusing the torque/horsepower equal, which is 5252