Mercury 115 2+2

[esox-lucis]

Hello, I just purchased a 1992 Starcraft SFFM 170 with a 1992 Mercury 115 2+2. The test drive was very sluggish and not much top speed with lots of rps. Inspected the prop and determined it was a 10 pitch. The owner said his wife replaced it last summer for water skiing. My search has shown a 22 pitch to be correct for this setup. My question is thought for the best prop for water skiing 3 or 4 blade, stainless, pitch?
TIA Jim

 

[flyingscott]

What is the health of the motor? A 19" pitch aluminum would be a good all around prop for that. Your MAX Rpms should be 5250. A 10" pitch should have sent the RPMs through the roof. A 10" would be a terrible choice for skiing. I buy the Factory manual for that motor and start doing test.

 

[racerone]

Wow----A 10" pitch ?-----So I would start with a compression test.----Post your numbers here.-----Next is a peak out put ignition test.----Does spark jump a gap of 3/8" on all leads ?-----And you need to install a new water pump impeller before your next launch.

 

[esox-lucis]

What is the health of the motor? A 19" pitch aluminum would be a good all around prop for that. Your MAX Rpms should be 5250. A 10" pitch should have sent the RPMs through the roof. A 10" would be a terrible choice for skiing. I buy the Factory manual for that motor and start doing test.

Agreed the motor was screaming. I think the boat shop sold her what they had on the shelf not necessarily the correct one. Hour meter only shows 300 hrs and the boad/motor look like it's true.

 

[flyingscott]

Agreed the motor was screaming. I think the boat shop sold her what they had on the shelf not necessarily the correct one. Hour meter only shows 300 hrs and the boad/motor look like it's true.

I would be very careful about overevving that motor. Anything over 5250 and there is a great chance of breaking a piston skirt. Get a tach if it doesn't have one.

 

[jimmbo]

Those motors don't take Kindly to being run above 5800.
10" Pitch? That would be for pushing something like a Tugboat
Do what racer said.

 

[esox-lucis]

Those motors don't take Kindly to being run above 5800.
10" Pitch? That would be for pushing something like a Tugboat
Do what racer said.

I don't have the boat here yet, but plan on doing the tests this weekend. I will replace the waterpump this winter. I've been looking on a few prop finder sites for the correct prop for the boat. Looks like most are recommending 13 x 21P. Since the primary use for this boat will be water-skiing many people recommend The mercury high five prop for skiing giving up some top speed. I know with a 4 blade the recommendation is to drop one pitch. So would a 20P high five be a good choice? I see a used one is available fairly local I could try. Would pn 48-816612A45 fit on the 1992 115 hp? Thanks Jim

 

[jimmbo]

I don't have the boat here yet, but plan on doing the tests this weekend. I will replace the waterpump this winter. I've been looking on a few prop finder sites for the correct prop for the boat. Looks like most are recommending 13 x 21P. Since the primary use for this boat will be water-skiing many people recommend The mercury high five prop for skiing giving up some top speed. I know with a 4 blade the recommendation is to drop one pitch. So would a 20P high five be a good choice? I see a used one is available fairly local I could try. Would pn 48-816612A45 fit on the 1992 115 hp? Thanks Jim

It should fit.
However, I am not a 4 or 5 blade fan, 3 is the Maximum number of Blades I would ever look at. And all the boats I or my Family have ever owned had 3 blade Props, except for the 5 1/2 which had a 2 blade. And the 25hp, 35hp, 40hp, 90hp, 115hp, 150hp, and current 260 I/O all pulled skiers without issue. My 84 115, even pulled a one guy out of the Water without any Skies, and that was done using the 3 blade Prop that was always on the motor, and allowed it to hit the top of the Rpm range. That was a 19in. but yours has a slightly different gear ratio than it had, so a 20 might work. I guess if you don't like the outcome, you could just list it on flea bay...

 

[Texasmark]

My 2002 115 2+2 has a 5250 rev limiter module. The serv. manual covers 1996 through the end of production so I don't know if the '92 version had one or not.

A 3 blade prop is multifunctional and made for fast running as a design objective. You can get ported props, holes under the leading edge of the blades which allow exhaust blowby, decreasing the density of the water and allowing RPM increase much faster resulting in a better hole shot, but it is slip and wastes gas. I had such on my bass boat and slalomed behind it often......but I bought that boat to run, not cruise and propped accordingly.

A 4 blade is a stern lifting prop made for things like cruising and midrange running plus water toys. Solace, for one makes both kinds and advertises as I mentioned as to the targeted application. I took my 20" 3 blade Laser II off and installed a 19" Solace 4 blade.

My current boat, is a 2002 Crestliner 1750 Fish Hawk, and changing props followed the rule. I remained just under the RPM limiter 5250 with both props and cut my WOT from about 48 to 45 MPH running alone (for a data point), which was a couple of MPH better than I expected, with a strong hole shot and nice controllable mid range where I do most of my running these days.

 

[Texasmark]

It should fit.
However, I am not a 4 or 5 blade fan, 3 is the Maximum number of Blades I would ever look at. And all the boats I or my Family have ever owned had 3 blade Props, except for the 5 1/2 which had a 2 blade. And the 25hp, 35hp, 40hp, 90hp, 115hp, 150hp, and current 260 I/O all pulled skiers without issue. My 84 115, even pulled a one guy out of the Water without any Skies, and that was done using the 3 blade Prop that was always on the motor, and allowed it to hit the top of the Rpm range. That was a 19in. but yours has a slightly different gear ratio than it had, so a 20 might work. I guess if you don't like the outcome, you could just list it on flea bay...

Well Jimmbo one September day in 1973 we had a company picnic. I had a New 1972 Johnson 125 (power tilt but no trim...that came out with their '73 year model} with the newly released 17P OMC SST 3 blade (non ported) prop on an 18' Caravelle tri-hull. It took some doing but I, alone in the boat, was able to get 5 skiers (I think at least 3 of them were light weight and on 2 skis, possibly all as I don't remember) up and ran for a couple hundred yards before the first fell off and ended my showing off. We were out fooling around and were testing Mercs against OMC and it just happened.

 

[QBhoy]

Hi. That’s way way wrong for that set up. You’d be wanting a minimum 19” and likely a 21” to see where you are with either of them. If the engine is healthy, she should manage that no problems. I’d do a compression test on her to make sure.

 

[esox-lucis]

Wow----A 10" pitch ?-----So I would start with a compression test.----Post your numbers here.-----Next is a peak out put ignition test.----Does spark jump a gap of 3/8" on all leads ?-----And you need to install a new water pump impeller before your next launch.

OK I did a compression test. From top to bottom 90, 89,90, 90 I did not have the carbs held wide open when testing
Spark was good.
Put a 21p prop on and going to try it this afternoon

 

[racerone]

Carburetors do not need to be open on a 2 stroke like that.-----Compression seems low.-----Taken at what elevation ?

 

[esox-lucis]

It did 45mph GPS typped out at 5100 rpm according to boat tach. Ran good.

 

[esox-lucis]

This boat really likes to put the bpw in the air coming out of the hole. Do you have any experience with the hydro wings on the motor? Also, Where would be the best place to get a water pump kit from for this motor?

 

[Texasmark]

It did 45mph GPS typped out at 5100 rpm according to boat tach. Ran good.

You are right where you want to be.