24ft pontoon. 115hp mariner typical prop?

[dmoriarty51]

Hey folks, I have picked up a 1993 Fisher Freedom 240 Dlx it has a 115hp 4 cylinder Mariner of the same age. What prop would you expect to run on it? Looking to get a ballpark idea is all I know I need to know rpm and weight to get accurate.

 

[Sea Rider]

Will depend entirely if combo will be used with few boaters or a complete family, that OB must revs inside its wot rpm range, if around middle to max wot revs much better with current load you expect to transport.

Happy Boating

 

[steelespike]

As a starting point a 11" pitch.
If it has a prop check the numbers under the prop nut.
11 May be a little light. But your better off light.

 

[dmoriarty51]

Are you thinking 3 or 4 blade steelspike? I will pull the current prop tomorrow to see but i'm guessing its at least a 15 pitch but appears on the small end diameter wise, the boat came with a few others but they are larger diameter and 15 pitch or greater. I will get tach readings as soon as i get it functioning properly.

The boat came from an older fella that just fished alot so i'm thinking slow was his standard procedure, I realize a 24ft pontoon isn't a speed boat but i understand the need to be propped correctly for the load.

 

[steelespike]

Other than a need to grip the water A 4 blade may not be necessary.
A 4 blade can improve grip and resist ventilation .The boat may respond better around the dock.
Again a 11" may be light.

 

[dmoriarty51]

Pulled the current prop this morning, numbers on the back of the hub are 48-16988-18 Google says its a mercury vengeance stainless 13 x 18 pitch 3 blade.

I do have a couple other options like

13 3/4in x 15p aluminum michigan wheel
12in x 18p aluminum unknown manufacturer
13in x 18p quicksilver stainless

I am going to borrow a tiny tach off another motor for this weekend if I can't get the in dash to work right, it floats a bit and shows idle at something like 4k rpm. my ear says more like 800-1000. The motor drank fuel like crazy last weekend, and sounded heavily loaded last weekend. I had probably had about 11-1200lbs on the boat people and gear at the time.

I'm thinking I should go ahead and drop to the 15p at least.

 

[steelespike]

As long as you have a 15 give it a try.

 

[dmoriarty51]

Tried the 15 yesterday, it sounds alot happier. Still no tach because I'm dragging my feet

 

[Sea Rider]

A lot happier is no indication is revving towards max wot range, ear tach doesn't work spot on as a real one..

Happy Boating

 

[dmoriarty51]

Ok its been a while but I finally got back to this. Got a new in dash faria tach appearing to work correctly. Ran the boat last Sunday and according to that tach it is reaching 5k rpm with the 15 pitch 3 blade aluminum prop, at 17-18mph gps indicated speed down river, i would place current at 2-3mph at this time. This appears to indicate 50% slip..... Either I still have a mis reading tach at higher throttle/rpm, a slipping hub or ? Going to pull the prop mark the hub and give it a shot in the coming days.