[blockp]

With your original prop you were able to get up on plane, right? If you put that one back on, does it still plane out?

If that still works, then defiantly not the coupler, but it doesn't make sense as to why the new prop wouldn't get you on plane either.

[abillmann]

Prop #1: 14" x 21p. Very good shape--no dings. Still, the boat wouldn't plane at all.

Since I didn't have a spare prop with this boat, at the suggestion of a repair place (and I agreed with them), I picked up a new prop because we all thought Prop #1 one was spun. Made sense at the time.

Prop #2: QuickSilver 14.5" x 19p. Brand new. The shop installed it, and I watched them do it -- no problem there.

With Prop #2, if I'm alone in the boat, it comes up and planes just fine. With three other people, no go. This makes sense, as the lower pitch would yield a little more power out of the hole. But still... not getting up on plane with 4 adults and a 4.3L /195 HP engine? I mean, jeez, my grandparents' old 55-horse Evinrude outboard could do that.

The engine seems to be making good power...it's not missing, sputtering, or anything like that. It's totally smooth. And there's a ton of wake and prop wash being produced also, so it's putting at least SOME RPMs into the water.

(Maybe the previous owner opted for Mariah's largely unsuccessful "newly improved hull lining, now made with extra lead!")

I'm totally at a loss.

[blockp]

So if it starts to over rev, the question is, is it ventilating or cavitating? Is your ventilation plate all in tact? Is the back of the new prop showing any burning or funny marks?

What model 19p prop did you get? Maybe has bad shape or too much/little cupping?

[abillmann]

The new prop is a QuickSilver Black Diamond XT Aluminum 3 Blade (14.5 x 19). Seems like a logical choice. I watched the tech take it out of the sealed box, so there's no chance it's a case of mistaken identity.

There was a hub kit as well, with all the associated hardware (locking ring, thrust washer, etc.). Everything was installed as you would expect. And for a tech with 20 years of experience putting a prop on a totally typical Alpha One, I mean, that's a no-brainer, right? I guess it's possible they grabbed the wrong hub kit and the thrust washer isn't the correct one, HOWEVER, the previous prop (the 21p) didn't require a hub kit and exhibited the same symptoms.

The ventilation plate is completely intact -- no problem there. And there's no evidence of burning or marks at the back of the prop. The skeg has a small chunk missing (maybe a half-inch by 2 inches) on the trailing edge, but there's no way that could be the problem.

[blockp]

Sure seems like it would be a fine all around selection. Nothing specialized about it that would make me thing it's a bad blade design for your setup.

"Recommended for speeds less than 50 MPH and applications less than 250 HP"

The different hub kits are just the internal metal part of the hub that connects to the splines on the prop shaft. If he had the wrong kit, it wouldn't have fit on the shaft. Basically makes it so the same prop can be run on a volvo as a merc... just swap out the hub kit.

I agree, I don't think that small of a piece missing from the skeg would make that difference.

I'm starting to agree with your assessment of having the new lead lined hull.



If the coupler is shot, you should smell the rubber burning when it slips.

Here's some text from iboats on how to test the coupler.
"WITH THE ENGINE OFF, shift into fwd and stand on a prop blade while having someone look at the inputshaft behind the motor. If it turns and the motor dosent, the coupler is bad."
http://forums.iboats.com/showthread.php?t=311043

[300sflyer]

After reading the tread so far, a couple of questions come to mind:

With just you in the boat, what is the WOT speed of the boat, and at what RPM? If the coupler was slipping, one would think it would be doing it when the engine is under load, no matter how many people are in the boat.

The next one might seem trivial, but when was the last time your engine had a tune-up? Just like our cars, a properly tuned engine produces more power, and runs a whole lot better! Is the fuel filter clean?

When was the last time the flame arrestor was cleaned? If it's dirty, it could be holding the engine back too.

Is there fresh gas in the tank? Old stale gas can create all kinds of issues.

Hope your problem is one of these simple fixes! Keep us posted.

[abillmann]

The engine really does seem OK. It had new plugs this spring, an oil change last fall (before being winterized) and the gas is fresh clean. (And less than half a tank, so the extra weight of a full fuel tank isn't coming into play.)

Not sure about the flame arrestor. Still, the engine seems smooth -- it always starts without a problem, doesn't hesitate or miss, doesn't sound clunky or rough.

With just me in the boat, the WOT RPM is about 4600. The speedo reports 44 mph, but I've yet to test it with GPS.

I agree with you about the coupler -- if it was going bad, it would be kinda obvious.

I'm taking the boat out now with my girlfriend to see what happens with two people. (For the record, she's 5'4, 130#, if that plays a role in any of your calculations.) I'll make a note of the WOT RPMs if we can get it to plane.

[Z 202]

Well I don't know, if you come back here and post up that you couldn't get it up with just the girlfriend, we may just have to refer you to a doctor, for some pills.

Back on topic; is your bilge empty? Check the ski locker too. There were some members who were missing a drain hole at the back to the engine compartment. Result was the ski locker holding a lot of water.

[abillmann]

OK.

With just my girlfriend and I, no problems whatsoever -- it quickly planed out. So apparently the problem is occurring when someone sits on the back bench seats.

Could an extra 200 pounds back there really cause a 195HP boat NOT to get up on plane? Especially if there's another 200 pound person up in the bow?

To answer other questions: Bilge is empty, ski locker is dry and contains only an old canoe paddle, trailer is definitely not still attached.

Last night, with the two of us, on calm water, WOT was 4400 RPM.

[300sflyer]

It still sounds to me like your engine is not making the power it should for some reason. Perhaps some kind of exhaust restriction? Just a guess...

How many hours are on the engine? Have you done a compression check? I'm sure this is not what you want to hear, but perhaps the engine is simply worn out?

Your boat should be able to pull a water skier out of the water, even with 3 or 4 people in the boat. Not sure if you tried that, but I can imagine the results based on your other comments.

If I were you, I would take an experienced marine mechanic for a ride in your boat along with 1 or 2 other people, and let him see what it does first hand. Perhaps then he would be better able to diagnose the problem.