Performance Question

[TooReel]

Engine in question is a 2004 Mercaha 225 4-stroke.

This weekend we loaded it up for a family fishing trip (Took the admiral, 14 yr old daugher, her best friend and the three year old out to a rock in 8' and they had a blast with the grunts and rock bass). Anyway, I noticed that it felt a little sluggish getting up on plane. I was running right at 4200 rpm's to maintain about 26 MPH in the channel. With my 17 pitch prop that is like 30% slip. Once we were in the gulf I pushed it up to my normal 32-33 MPH cruise and it felt fine. I forgot to note the engine rpm's at that point. Checked the prop and it had no fresh damage and with the high summertime water I have not done any rock bashing.

Is something going south in my engine? I was going to have it tuned up top to bottom after this summer but now I'm worried. Engine has about 500 hours on it now. I don't know what was done before I bought it but I've only had the oil, fuel filter, impeller and lower unit oil changed since I have owned it.

[TooReel]

Just put the boat in the water and did some more testing. At 6000 I'm running 42 mph and at 5000 she's running 33. My prop is a mirage 17 pitch so I'm not sure if I should calculate it at 17 or 18 pitch with the cupping but it works out to be

17p 18p

6000 rpm 42 mph 13% slip 17% slip

5000 rpm 33 mph 18% slip 22% slip

Boat Test magazine reported 5000 rpm and 41 mph with their 2004 boat set up like mine. That is like .037% slip with a 18 pitch prop.

Last October I hit a rock so hard it spun the hub and it (the hub) had to be replaced. Just the tips were bent and we hammered them out but I'm guessing my prop is shot and just wasn't as noticable since I've had the boat loaded light until last weekend.

[prober]

Yeah you could be right. Might see if you could try another prop before you spend the money though.

[ken2]

There is nothing wrong with your motor. RPM and prop slip is directly related. your engine running poorly can't make a prop slip more.

If all the load was in the back, and it wasn't solidly up on plane at 26, the slip will be higher. Don't know what kind of boat you have though.

You could take that prop to a good shop and see if they can referbish it and make it run well again.

As for the prop slip calculator, all props are cupped a little now days, I'd just stick with the pitch thats stamped on the prop.

[TooReel]

Boat is a Trophy 2103. Load was pretty even as I the cooler and live well are in the back, wife and I in the center and the two girls up front. Here is the running shot from that day.

There is nothing wrong with your motor. RPM and prop slip is directly related. your engine running poorly can't make a prop slip more.

If all the load was in the back, and it wasn't solidly up on plane at 26, the slip will be higher. Don't know what kind of boat you have though.

You could take that prop to a good shop and see if they can referbish it and make it run well again.

As for the prop slip calculator, all props are cupped a little now days, I'd just stick with the pitch thats stamped on the prop.

[Boz]

It's a real long shot, but looking at the picture, the top of the motor cowl appears to be almost parallel to the water, while the bow is still fairly high, indicating that the engine was trimmed upward. Have you tried trimming the motor down a bit more to see if it brings the bow down, thus getting into more of a full planing attitude?

[TooReel]

It does look like a lot of trim. I just kept bumping it and watching the gps until I got the max speed.

My motor is a little low when I watch the cavitation plate. I have one hole left to move it up so I'm going to see about getting it raised. That might be why it likes the trim.

It's a real long shot, but looking at the picture, the top of the motor cowl appears to be almost parallel to the water, while the bow is still fairly high, indicating that the engine was trimmed upward. Have you tried trimming the motor down a bit more to see if it brings the bow down, thus getting into more of a full planing attitude?

[TooReel]

Borrowed a 18" enertia this weekend. No noticable difference. I guess that with the heavy four stroke, fresh water tank and fuel tank in the back makes it a stern heavy boat that does not like going 25 mph.