Trim won't stay DOWN under Power?

[h20mobius]

Hi -

I have a 20', 1995 Maxum with a 5.0L Mercruiser and Alpha 1 Outdrive; original Owner. Recently I've noticed my trim seems to creep "up" under power and the boat begins to "porpoise" shortly thereafter. I can press the trim down button for 1-2 seconds and it resolves... then 10 second later starts creeping up again. I've seen a lot of posts about trim not staying up, but very few about it not staying down.

Earlier this year I switched to a 4blade 17pitch prop, and have been running a Stingray foil for years now.

Any suggestions on where to start? We're nearing the end of our summer here in the Pacific Northwest, so I'd really prefer not to pull the boat from the water just yet, as it will be in the shop for months.

Thanks!

 

[QC]

Re: Trim won't stay DOWN under Power?

Sounds like a sticky or flakey switch to me. I've seen a Volvo handle do this once before . . .

 

[Fordiesel69]

Re: Trim won't stay DOWN under Power?

Pull the foil for now until you can resolve the problem. The valving for this is internal to the trim cylinders I beleive in that year. Are you loosing fluid or does it look milky?

 

[Don S]

Re: Trim won't stay DOWN under Power?

You aren't for some strange reason running a counter rotating drive are you?

 

[h20mobius]

Re: Trim won't stay DOWN under Power?

Pull the foil for now until you can resolve the problem. The valving for this is internal to the trim cylinders I beleive in that year. Are you loosing fluid or does it look milky?

Fluid is nice and dark, and level hasn't dropped. Foil has worked great for years... just out of curiosity, why do you suggest pulling it if the problem just started? Will that help me diagnose?

 

[h20mobius]

Re: Trim won't stay DOWN under Power?

You aren't for some strange reason running a counter rotating drive are you?

I am not. Single prop.

 

[h20mobius]

Re: Trim won't stay DOWN under Power?

Sounds like a sticky or flakey switch to me. I've seen a Volvo handle do this once before . . .

Spent awhile yesterday trying to rule this out... and think I have logic to exclude it. Under power and when it begins to porpoise, you can still hear the trim motor if you press the up/down button and have someone with an ear near the transom. If it was a faulty switch, I would think I could hear the trim raising slightly... and that it would do so anytime the engine is running, not just at higher (waterskiing) speeds. Correct?

 

[Don S]

Re: Trim won't stay DOWN under Power?

I am not. Single prop.

The reason I ask, the direction of a prop pushes the outdrive down when in forward. Without the pump running, there is absolutely no way for the pump to lift up against the force of the boat going forward.

 

[h20mobius]

Re: Trim won't stay DOWN under Power?

The reason I ask, the direction of a prop pushes the outdrive down when in forward. Without the pump running, there is absolutely no way for the pump to lift up against the force of the boat going forward.

Very interesting. The electric pump is definitely not running when it starts to porpoise (it's rather noisy, so you can hear it pretty easily). This configuration has been great all summer until last week.... haven't changed a thing in terms of prop, foil, # of people, body of water, etc. Prop is still in great condition and free of damage.

Out of curiosity, what is your opinion on this potentially being a partially spun hub on the prop? As I mentioned, pressing trim down resolves the problem when it porpoises, so that's why I assume it's been raising. I dont know for certain that the trim is actually raising, as there is no trim gauge. I also feel like the boat has begun to cavitate more easily since last week - especially on tight turns...

 

[Fordiesel69]

Re: Trim won't stay DOWN under Power?

The foil will provide lift on the drive. That is the only thing you have installed that could possibly raise the drive. If anything the drive will lower itself if there is a trim problem.

 

[h20mobius]

Re: Trim won't stay DOWN under Power?

The foil will provide lift on the drive. That is the only thing you have installed that could possibly raise the drive. If anything the drive will lower itself if there is a trim problem.

Thanks FordDiesel... the foil has been installed for years without a problem. The foil/prop combo worked beautifully up until last week, so there is some other variable contributing to the issue, right? Just trying to get to the ROOT cause, which is obviously not the foil.

 

[Don S]

Re: Trim won't stay DOWN under Power?

Out of curiosity, what is your opinion on this potentially being a partially spun hub on the prop?

A spun hub doesn't work at all, a good hub works, A partially spun hub works just like a good hub until it suddenly becomes a spun hub.

When you pull a skier (or anything else for that matter) there is more drag on the back of the boat.
Adjusting the trim for different conditions is why drives have trim to begin with. When things change, weight, load, load distribution, etc. you will have to adjust the trim. That's just the way it is and why they put trim on boats.
Look at it this way, if one position would do it all, you would have up and down. No need for trim.

 

[h20mobius]

Re: Trim won't stay DOWN under Power?

A spun hub doesn't work at all, a good hub works, A partially spun hub works just like a good hub until it suddenly becomes a spun hub.

When you pull a skier (or anything else for that matter) there is more drag on the back of the boat.
Adjusting the trim for different conditions is why drives have trim to begin with. When things change, weight, load, load distribution, etc. you will have to adjust the trim. That's just the way it is and why they put trim on boats.
Look at it this way, if one position would do it all, you would have up and down. No need for trim.

Thanks... I realized that I guess... had just read on another forum where someone had similar symptoms and they diagnosed it to be a slipping hub. I've been finessing my trim as I pull skiers, boarders, more people, etc for nearly 20yrs... I feel like I have a good grasp on how it works holistically in the system, how the hyrdaulics work in principal, the foil, etc... which is also why I'm so baffled. Since holding the trim down seems to temporarily solve the problem, I have to believe it's related. Maybe I'll have to yank her early this season...