Prop cavitating - GW Tournament 19

[gigem]

Hello!

I just got my 1987 Grady White Tournament 19 back in the water today. It got a motor swap - took off the original 1987 Johnson 140 and replaced it with the 1995 Evinrude OceanPro 175 that came off a Whaler I just sold.

Mounted the "new" motor in the same position as the old one. Put it in the water today for the first time. Prop blows out quickly, pretty much whatever I do with the throttle, unless the motor is trimmed all the way down. When it's all the way down, I can get the prop to bite but I have to be very careful with the throttle. Baby it up to speed. Forget holeshot, not with this setup.

I will say that once I got it moving, I hit a max of 44 MPH at 5500 RPM's, for whatever that is worth.

So as I am sitting there floating in the ship channel, trying to think of what the issue might be, I remember that the old Johnson 140 had a Doelfin hydrofoil on it. I bought this boat used, about 20 years ago. That fin has been on there so long that I forgot about it!

Now I am thinking that this boat blew out the prop when it was new, and the previous (original) owner put the wing on to address it. And it was addressed, as the old 140 ran great for many years.

I know that some people say that hydrofoils are a bad idea, and a bandaid to address an underlying problem. Motor mounted at the wrong height. Wrong prop. Bad hull design, etc.

The Evinrude OceanPro and this prop ran like a top on my Boston Whaler Outrage 21. This Grady is different, of course. Deeper V.

My inclination is to go get another hydrofoil to install, as opposed to playing the prop changing game and/or changing the height of the motor. Lazy? Maybe...

Any thoughts? Any particular brand of hydrofoil you recommend?

Anyone else have this problem on a Tournament 19?

 

[fishbust]

The foils are usually better on the I/O's.

It will not do anything to help you if the motor is too high. It will raise the stern faster, which would make the problem worse.
The motor should be down when planing. That is right but you should not have to baby it in that position.
I would lower it a notch.

 

[DennisG01]

Do both motors have (had) the same shaft length?

I agree, don't mess with adding anything. Adjust the height of the engine. Actually, often times a fin can CAUSE ventillation or prop blowout. It worked with the old engine, but don't assume that engine worked because of the fin.

 

[gigem]

Do both motors have (had) the same shaft length?

BINGO! I am actually going to close this thread and start another one, based on the weird stuff I learned today...

 

[gradydriver]

We always start with the motor trimmed all the way down..... :-|

 

[BobP]

A buddy had a 19 ft Grady with an old carb Yami 225 on it. Except for being a gas pig. it sure was that, it could move.

You are not cavitating.

 

[mboyatt]

Did you all read the entire thread?? As DennisG predicted, the motor shaft was too short for the transom on the boat. Don't know how he suspected that one, but he hit it. :hmm

 

[DennisG01]

Sometimes a guy just gets lucky!

Actually, it didn't make sense that a fin was making that much of a difference. If anything, it would of caused the cavitation, not prevented it. Since you've had experience running boats, I figured you were on top of things in terms of trimming. There could of been something fouling the prop, but I also figured you would of seen that. After all that, I figured it was a combination of just a simple mistake of not checking the shaft lengths and excitement to have a new motor and get out on the water and play. In the end, all it took to figure it out was some simple "boat logic"... Which isn't always logical.

 

[fishbust]

Definitely not logical Dennis.
No one would guess that one. Who would hang a different size motor and not know it? People can see where the anti-ventilation plate is and know where it needs to be in relation to the hull, depending on setback, give or take.
The issue is usually just being 1 or 2 mounting holes away from being dialed in.

He could have also been starting to spin the hub with those symptoms.

 

[DennisG01]

Thought about the hub, but since he was able to reach full speed I discounted that. Maybe others have had different experiences, but mine has been that with a slipping hub you can't accelerate fast nor reach full speed. Figured it would be obvious to tell which holes to use since there would be wear marks. The next thing that I thought about was "Hey, I wonder if this guy was so excited to get a new motor on the boat that he never checked the shaft lengths". I agree - kind of an obvious thing to not notice, but we've all done some strange things... or at least I have!

I once dried my sneakers on the engine of my wife's BMW while it was in the garage. I figured it was "free heat" and if I gently lowered the hood (but not latch it... hint, hint to what's coming, if you haven't yet figured it out) that they would dry even faster since more heat would be retained. Later that night I took her car to the store. Everything was fine until about 40MPH, then... WHAM!!!! Holy crap!!! Turns out that drying your sneakers on your engine isn't so "free" after all. Yup, done some stupid stuff in my day. And, yes, it's OK if you feel the want to laugh at my expense. I did.

 

[mboyatt]

So let me get this straight. You were drying a 20 dollar pair of sneakers under the hood of a 50k car, and forgot to remove them when you took the car for a spin. Two questions. Were you on a beer run? And are you still with your wife? So I guess the shoes went into the cooling fan?? Dang! :<><

 

[DennisG01]

Hey now. They were $45! :lol:

Nothing so noble as a beer run. Just milk and bread. Not the fan... the hood flew straight up!!!! Didn't hit the windshield, but it bent the hood and the hinges. The shoes were dry and still laying nicely on the engine. :roll:

 

[TonyD]

That is one funny $#% story, Dennis!! lol

Anyways - so now that I have the boat back in the water.. I have a new problem that did not exist last year - some cavitation or ventilation. I bought a new yamaha 150 - had a service dealer install. All last year everything ran fine. But now, it seems the prop is slipping. The RPM's are up there, engine sounds fine but I lose speed. It's also not consistent - I am trying to nail down when it happens but mostly at full speed - when I turn.. not really sure. And then sometimes, it doesn't happen at all. Very strange.

I plan on taking the boat out of the water again to check to see if the aviation plate is centered with the keel but I don't suspect that to be the problem. I know very vague with my symptoms here but does anyone have any thoughts on this?

 

[mboyatt]

Not too clear on what you are saying. I think you are indicating that you had the Yamaha installed last year and that it ran great all year with that prop and set up. If that is the case, then I doubt seriously that you have a prop issue or issue with the height of the motor. If it ran fine all last year, then I would look to a fuel issue. I have an evinrude ocean pro, so I can't speak to the Yamaha. You would need to check your filters on that model and make sure you do not have a restriction elsewhere in the fuel lines. Lastly, the fuel pump. I would start with ruling out the easy stuff first - filter, no leaks or restrictions in the fuel line, good primer bulb, etc. Good luck!

 

[TonyD]

Hey mboyatt - yeah just to be clear, I don't lose power on the engine, otherwise I would just bring it back to the serviceman since I am still under warranty.

For example, my RPM's were up at 4000 but my GPS speed read 13mph. The engine itself isn't losing power, it sounds just the way it should, not misfiring, no choking, no loss of engine power - it does seem like the prop is losing it's bite.
On my old engine, I spun out my prop once - that is exactly how it feels. However, I checked that all out, the prop is fine so I am assuming some kind of cavitation or (I heard of a new term called) Ventilation.

I also checked for weeds wrapped around the prop, threw her in reverse to blow anything off but nothing and still had a bit of an issue. But also like I said, it doesn't seem to be consistent - yesterday afternoon, I was out all afternoon into the evening, took the kids tubing for awhile, then ran about 6 miles up the lake and then back with a little more running around and nothing. Everything was fine.. :head scratcher: