1977 mercury 115HP Max Rpm

[Gomer50]

I have a friend call me today and ask me about his boat,so I would like to pass this on to you guy's for your opinion..He has a 1977 Merc.115 HP on a 14 1/2 foot Hydro boat weighing about 420 LBS.Also he is running a 13 1/4 by 21 Pitch Prop and he say's his Motor is screaming at 6000 RPM WOT and GPS shows 41 MPH.I think he should be cruising alot faster than this.From what I have gathered this motor shouldnt be running in the 6000 RPM's not good for them.So the question is should he think about reprop (more pitch/more speed and lower Rpm)?? Or regear the lower unit from a 2.0 gear ratio to maybe 1.78. Any advise would be appreciated.

 

[Wingedwheel]

Re: 1977 mercury 115HP Max Rpm

You should post in the prop section. There's guys there that can give you a much better opinion on your prop pitch there. even so, I don't think a prop with the wrong pitch would allow the engine to scream unless its missing the blades..

 

[Chris1956]

Re: 1977 mercury 115HP Max Rpm

I have some experience with that prop/motor set up. Something is wrong. You should see 50MPH or likely more at 6000 RPMs. Is the prop damaged? Is the hull hooked?