115 merc 4 stroke efi on 32 ft party cruiser, what rpms should be at WOT

[kenbob62]

boat is new to us so we have no info on this 2005 party cruiser,i havnt had it wide open since I don't know what rpms is supposed to run at , currently im running at 11 mph at 4100 rpms when cruising, not even sure we have correct prop since previous owner was a complete bonehead ! 115 merc efi 4 stroke.... btw WOT stands for wide open throttle, thanks in advance

 

[MH Hawker]

i am not sure of the exact rpm but i would guess 5000 to 6000 thats a common rpm

 

[HotTommy]

There is a Mercury engine forum here on iboats.com. Perhaps someone there can answer the question.

 

[ahicks]

You would set it up with the same rpm you would use if it were on a ski boat, or any other boat. You always prop for the engine's max safe rpm at wide open throttle.

 

[G Wally]

I know I'm a little late but I have 2012 Lowe tri toon with a Mercury 115 efi 4 stroke and my book says 6400 rpm at wot. But I believe you said yours is a 2005 it may be different? Like you I had no info on my boat ( it was used) I was able to order a book on my motor from a Mercury dealer. As for the prop I used the Mercury prop selector to match a new prop to my boat.

 

[rickdb1boat]

WOT is 5000-6000 RPMs on the 115 HP. Prop near the top with a normal load onboard. What pitch prop are you running now?.Running at that low of RPM will shorten the life of the engine. Make sure the engine is running it's best before switching props...

 

[kenbob62]

the only thing I can get off the prop is 2050p11 quicksilver,eng runs great,we usually have 3-4 people when cruising,i I am in the process of adding a third pontoon so I havnt finished the installation yet,we boat in Barnegat bay wich can get very rough and windy that's why I am adding a third toon

 

[BigDfromTN]

the only thing I can get off the prop is 2050p11 quicksilver,eng runs great,we usually have 3-4 people when cruising,i I am in the process of adding a third pontoon so I havnt finished the installation yet,we boat in Barnegat bay wich can get very rough and windy that's why I am adding a third toon

I would bet that is an 11" pitch which should be very close on a pontoon/tritoon.

As others have said, prop it to close to upper end of RPM range with normal load at WOT.
To possibly clear up one post. It is fine to run your engine at less than WOT as long as it is propped correctly. IF you were only getting 4100 at WOT then you have too much prop for that setup.

I just sold a 24' pontoon with a 2005 Merc 90 4stroke and it was propped to max at 5800 and would run 21mph gps lightly loaded. If you do change props check out a four blade. I went to that and really liked how it handled on my pontoon. Improved grip and low speed handling.

Enjoy your boat!

 

[Silver Eagle]

I hope that you have a tack .Run it at the rpm just below the red mark on your tack high yellow.. When I had my pontoon boat I ran it at 3700 rpms and got around 16 mph on bay waters. I had a 24 ft boat with a 90 hp 2 stroke Mercury. Some times when I wanted to bring the front end out of the water I'd punch it up to 5,000 rpms and it would hit 22 mph..It was an 2007 StarCraft and it was big and heavy.

 

[lmuss53]

Max RPM for every year of Merc 115 4 stroke I can find is 5000 to 6000, SO, you should prop the boat to run at or right below the 6000 rpm mark, with the throttle wide open and the boat loaded as you would usually load it. Get the prop that gives you the correct WOT range for your boat and motor combo, top speed and everything else will fall where it will.

I would not recommend continuing to run that motor wide open at 4100 rpm. Think of it as if you had a little 100 hp 5 speed car and you dogged it down climbing hills, with the throttle on the floor and struggling in high gear. That is what you're doing to your boat motor running it wide open and way below the recommended range.