What RPM range is safe for WOT on '93 Mercury 115HP

[convergent]

I just bought a boat with a '93 Mercury 115HP and the former owner put a new prop on it. I'm just curious how many RPMs I should be turning at WOT... what is a safe range for this motor?

 

[Barnacle_Bill]

Re: What RPM range is safe for WOT on '93 Mercury 115HP

4750-5250 according to the book.

 

[convergent]

Re: What RPM range is safe for WOT on '93 Mercury 115HP

OK, I'll have to check it the next time I go out. I could have sworn I was up around 5000 rpm and not all the way wide open. I just bought the boat so don't want to mess anything up. Should a boat be OK to run at WOT for a period of time? I know you wouldn't do that with a car, but is that normal in a boat... assuming I'm not exceeding the RPM range for WOT? I don't intend to do it all the time but just wanted to know if it was safe?

 

[convergent]

Re: What RPM range is safe for WOT on '93 Mercury 115HP

I got back out on the water today and I think I'm hitting closer to 5500 at WOT. I didn't let it stay there, but that seemed to be where it was going to stay... maybe even a little higher. Is this anything to be concerned about. I don't have a problem keeping it off WOT so I don't over-rev it, but not sure if a boat is supposed to be OK at WOT on a regular basis... if so, maybe my prop needs to be changed.

 

[pokman]

Re: What RPM range is safe for WOT on '93 Mercury 115HP

I got a 94 125 and my manual says 90,115,125 are 5000-5250rpms

 

[emckelvy]

Re: What RPM range is safe for WOT on '93 Mercury 115HP

The 4-cyl's are nothing like their eager-revving Tower of Power 6-cyl predecessors.

You do not want to overrev this motor, there's a potential set up destructive harmonics in the crankshaft, possibly breaking the crank.

Best to stick to the mfr's recommended rpm range, if you have the need to carry heavier loads prop it to the upper end of the range with just the driver in the boat.

HTH...........ed

 

[convergent]

Re: What RPM range is safe for WOT on '93 Mercury 115HP

The 4-cyl's are nothing like their eager-revving Tower of Power 6-cyl predecessors.

You do not want to overrev this motor, there's a potential set up destructive harmonics in the crankshaft, possibly breaking the crank.

Best to stick to the mfr's recommended rpm range, if you have the need to carry heavier loads prop it to the upper end of the range with just the driver in the boat.

HTH...........ed

So what change would I make on prop to slow the RPMs down a bit. I was in the boat with just myself and my 14 year old daughter when I tested it yesterday. Combined weight is under 300 pounds between the two of us.

I assume this would slow down the top speed, so guessing that it would increase the "pull" at takeoff.

Sorry for all the questions. I'm just anticipating one of my 4 kids (age 14-23) at some point deciding to run WOT for an extended period and I end up with a yard ornament as a result. They all seem to have a heavy foot in the car... wonder where they got that from???

 

[verado7]

Re: What RPM range is safe for WOT on '93 Mercury 115HP

find the current "pitch" number on your prop each pitch higher will reduce about 200 rpm - example if your current prop is a 17 pitch and your rpm is 5500 - an 18 pitch prop will bring rpm down to 5300, - you want to get it close to max - 1 or 200 rpm higher isnt going to kill your motor - if its a 2 stroke .

 

[milehighboater]

Re: What RPM range is safe for WOT on '93 Mercury 115HP

I use a pro pluse adjustable prop and it works well on my 75hp. I use my boat for a range of uses in varing altitudes and I can adjust the pitch with a allen key and about 10 minuites. Better yet if someone takes my bass boat into sand bar I can replace the blades individually for 20 dollars a piece. And I do know they can take a bit of trama before they snap off (from experence). Best thing about it is if you are doing a day of water skiing you can change the pitch for a great hole shot or if you are just running around you can pitch it for better fuel ecconomy. Either way a prop is going to cost you around 150-200 dollars.

 

[Dave1027]

Re: What RPM range is safe for WOT on '93 Mercury 115HP

My 100hp revs the same with a 17p ss prop. It works well for pulling up skiers. If you put a larger prop on to get the rpm range correct as the manual states you will struggle to pull people. Just don't hit 5500 and leave it there and you'll be OK.