'93 115HP Mercury - Prop Suggestion

[convergent]

I have a '93 115HP Mercury on a 17.5' Fish and Ski that I bought several weeks back. The owner put a new prop on it right before I bought it and I'm not sure if I want to change it. It is a 2040P21 Quicksilver which I measure to be 13" and assume the pitch is 21. At present, it doesn't perform bad, but at WOT it is going to go over the recommended RPM range which is 4,750-5,250. If I go WOT it gets to 5,500 and I back off... I think it would go higher if I let it. I don't have a problem just not going that high, but wondering if there is some more performance to be had.

My top speed now is about 45mph if the speedometer is correct, at about 5200 RPMs. I use the boat for fishing and skiing. For skiing, it gets lighter skiers up fine, but I tried this week to get a guy up that was about 215 pounds with 3 of us in the boat and we wore the poor guy out and never really got him up. I'm sure part of it was him not knowing what he was doing, but seemed like we were dragging him a bit. I am 190 and intend to try slaloming behind this thing, so a good tug is going to be needed.

So my understanding is that if I go up to a pitch of 23 and maybe a 1/2" or more larger prop, that it will slow down the RPMs at WOT a bit. Will this increase top speed or lower top speed? Will this increase low end pull, or decrease it? What about a 4 blade prop or going stainless? More or less speed, and more or less pull?

 

[ono_55]

Re: '93 115HP Mercury - Prop Suggestion

Had the same problem with my boat went form a 21 to a 17 degree prop.The 17 degree prop will give you more pulling power down low.

 

[steelespike]

Re: '93 115HP Mercury - Prop Suggestion

With your rpm and sking problem you might consider a 4 blade in the same pitch.
Will lower your rpm slightly,improve your hole shot,stay on plane with less power
handle better around the dock.It will allow a higher motor installation and higher trim.It may cost you a little top end

 

[convergent]

Re: '93 115HP Mercury - Prop Suggestion

That's kind of what I was thinking... go with a 4 blade stainless same pitch and diameter. I am not that worried about the top end, although I have a question on that. I will need to be around 35-40mph for me to ski on one, based on past experience. At 190 pounds do you think I'll loose enough top speed to take me below 40 at WOT while pulling a skier?

Another idea... what if I went with a 4 blade with one pitch lower. The 4 blades will slow down the RPMs a little on the top end, right? So I could go down one more on pitch possibly. I wish you could rent a prop or something to try out and see if it gave the results wanted before buying.

 

[steelespike]

Re: '93 115HP Mercury - Prop Suggestion

Nothing is concrete in a prop change.To me based on your present rpm
The 4 blade will solve it all and (probably maintain your 40 mph limit.
I feel your speed will survive well.