Need more speed

[RandS]

New boat owner, bare with me. I have a very used, 2000, I/O, 20 ft ski boat with a 5.0 mercruiser engine and a 22” prop. It’s top speed with me and two kids, and almost no gas, with the wind at our backs is 29 MPH (GPS) and 3900 RPMs. I feel like it should be going much faster, does this sound about right? Is there something we can do to add some speed? We were told a small prop would help but it wouldn’t have as much power at take off (I, personally, don’t think it has enough as it is). I’ve been driving jet skis all of my life that go much faster, so that’s just what I’m used to.

 

[matt167]

re prop it for sure. I would also verify the drive ratio's correct for the 5.0L and make sure someone didn't mismatch the leg. Also check the tune.

The only other possibility I can think of is being water logged

 

[Scott Danforth]

You have the wrong prop and you may have motor issues. A 15x19 3-blade max, maybe less with your boat. You should be hitting 4800-5000 rpm



Do a compression test as well

 

[achris]

...We were told a small prop would help but it wouldn’t have as much power at take off...

Hello RandS, and :welcome: to iboats.

Whoever is telling you these things hasn't got a clue! A smaller pitch prop will give you MORE acceleration, especially at take-off, so stop listening to them!

You need to evaluate the engine, check compressions, check timing, check the carb/throttle body is opening fully. If all these are right, and the engine is performing correctly, then you need to drop down a few inches of prop pitch. Based on your current 3900rpm WOT, look for something around 18" or 19" pitch.

Chris.

 

[Leardriver]

You aren't even getting into that engine's power band. You have 60 more HP that is not being used. Like Scott said, try a 19 pitch prop. Any aluminum will do. Buy one used online or borrow one for a quick RPM run. If that drastically improves your hole shot, top end speed, and RPM, you are on the right track and can fine tune from there.

 

[Scott Danforth]

actually the OP is severely lugging the motor

in my 19' boat (3600# dry weight) with a 5.0/Alpha combo. the biggest prop that i could use was a 15x19 stainless. anything larger and the motor would fall on its face. with just myself, 1/2 tank of fuel, i could hit 49.5mph at 4900 RPM on dead calm water.