I/O RPMS seem way too high.! Any ideas?

[Stevencpa]

I recently bought my first boat. It is a 1998 -22 foot walk around cuddy with a 4 cyclinder Mercruiser I/O and an Alpha one outdrive.<br /><br />I realized that this boat is under powered since I think it is around 130 – 150 horsepower (I don’t have the manuals). Can someone tell me what RPM’s a boat of this size and power should be running at to get it to only about 20 mph. I only go out with 2 adults and 3 small kids. My boat seem to need about 4500 RPM’s which seems way to high to run this motor for an extended period of time. I have played with trimming the engine and can’t get it any better. The prop is in good shape. Is this normal? Is it bad for the engine? Please let me know what other boats of this size run at (RPMs). Anybody have any other relatively inexpensive ways to help me? Any and all comments or ideas would be really appreciated since I am new to boating. Thanks for your answers !

 

[tommays]

Re: I/O RPMS seem way too high.! Any ideas?

your WOT (max rpm) is about 4800 <br /><br />is that speedo speed or GPS speed <br /><br />i have a 3.0 on a maxium 2000SC its about 19'and run around 41 mph at 4800<br /><br />what is the make of the boat ?<br /><br />with a boat that big and the load i would think you might get into the 35 mph range if everything is correct<br /><br />so the first question is that your max RPM or do you not want to go higher ?<br /><br />is the boat trailered or left in the water ? and what kind of shape is the bottom in CLEAN ?<br /><br /><br />tommays

 

[Stevencpa]

Re: I/O RPMS seem way too high.! Any ideas?

THanks for the response. THe boat is in the water but the bottom was just painted. It is clean. The max RPM is about 5,000 but the engine is screaming and I think 4,500 is too high to run. Speed is by speedo but I think it is accurate since I seem to be the slow boat out there. The boat is a Eurosport (out of business, and little info available).

 

[KaGee]

Re: I/O RPMS seem way too high.! Any ideas?

FYI... My indash speedo showed me going 15 while my depth finder said 21.3 and the GPS said 20.5 @ around 2400 RPM with a 3.8L, 175HP V6. That is a desrepency of around 30%. My boat is about the same size as yours, but that was with two people on board.<br /><br />These guys are better with set-ups than me, but seems like you are leaving a little on the table. But, I would not trust that Speedo at all.

 

[tommays]

Re: I/O RPMS seem way too high.! Any ideas?

current boats like that usally have a 4.3 or bigger as the base motor (trophy 2052/2352)ect<br /><br />what is you current prop size <br /><br />asumeing your rpm is correct the only thing you can try is the next size bigger prop<br /><br />if you can locate a local prop shop many will let you test props as long as you bring then back as good as they left<br /><br />i dont like to run above 3800 to 4000 rpm but thats just me <br /><br />tommays