Boat revs up and loses power up on plane

[badcarma58]

I have a 2002 Sea Ray 225 weekender with a 5.0L EFI motor and Alpha One i/o. Running 14x19 SS prop.

When boat is on plane, usually 3300 rpm and over, I have on mulitple occasions tried to trim the drive up. Every time I do this, out of nowhere, I will hear the rpms race up and feel speed decrease. I trim the drive back full down, and it goes away.

It happens at different points though. One time, I will trim up, and it won't race for a couple of seconds. Another time, I will trim up, and will immediately notice the rev-up.

It's almost like the it comes out of gear or the prop hub is spinning. I've taken the prop off to inspect, and all seems well. When put back on, it is properly torqued.

The problem is that when the drive in fully down, the boat is porposing. I need to trim the drive up a little in order to stop to porpoising, but that's when the boat revs and loses power.

Any ideas or suggestions?

 

[paultjohnson]

Re: Boat revs up and loses power up on plane

It appears you are getting prop ventilation. As opposed to a spun prop hub or bad engine coupler, as it does just when you trim up, correct ? I mean you can go WOT with the drive all the way down and it doesnt slip? Ventilation is when your prop catches air. Could be exhaust or just good 'ol air. Normally happens if the prop is to high [ as in an OB] turning to sharp, over trimming, or a damaged or incorrect prop. Whats the condition of your prop? Are you sure your not backwards on your porpoising issue ? Usually over trimming [drive up] causes that, not when its all the way down. Putting the drive all the way down normally stops that from happening.

 

[emilsr]

Re: Boat revs up and loses power up on plane

That's a dilly of a pickle...

It does sound like the prop is ventilating and that means you've trimmed up too far for conditions. Like Paul alluded to, a properly set up boat will tend to porpoise when overtrimmed, not when the drive is buried.....with yours doing the opposite there's some other problem that needs to be addressed. Sorry to answer your question with more questions, but here we go.....

1. When trimmed all the way in (down), is the drive tucked up to the transom enough to give the prop a slight (+ or - 10 degrees) down thrust angle? Could be that the drive isn't in the position it should be in.....check that first.

2. Sometimes this is a balance issue; do you have anything particularly heavy onboard that wasn't in the boat when they built it? Extra batteries? Lead porta potti? Try changing the weight distribution fore-aft (if you can) and see if this doesn't help.

3. What drive and prop(s) are you running? Sometimes a bow lifting prop can cause this; changing to a neutral or stern lifting prop may reduce or eliminate the porpoising.

4. Does the boat have trim tabs? If so, have you tried using the tabs rather than the drive trim to stop the porpoising?

 

[badcarma58]

Re: Boat revs up and loses power up on plane

The prop isn't showroom new. I just bought the boat, so it's still new to me. Only had it out a couple of times. When I had prop off, I filed down some of the dings in the blade edges. There wasn't really any damage to the prop that I could see.

If ventilation is the problem, I've never experienced it to this extent before. That is, by barely triming up the drive. I've experienced it in turns before on other boats, at low speeds. When it first occured, ventilation did cross my mind, but didn't really think it would be happening going straight forward.

I've experiemented a little, one day out, to see exactly what was happening and when it was happening. Like above, in one instance, the rev up happened immediatley after adjusting trim. In another instance, the rev up took a couple of seconds. If it was ventilation, wouldn't the rev up and power loss been constant? The speed, rpm's, and and lake surface were the same each time.

 

[emilsr]

Re: Boat revs up and loses power up on plane

If it was ventilation, wouldn't the rev up and power loss been constant? The speed, rpm's, and and lake surface were the same each time.

Not necessarily....even IF all the conditions (drive position, speed, throttle setting, wind, load, weight/balance, etc) were EXACTLY the same which is almost a mathematical impossibility.

 

[ziggy]

Re: Boat revs up and loses power up on plane

another vote for ventilation.
trimming up/out i don't believe will cure it. porpoising is the boat trying to climb up the wave (water) in ft. of the boat. then falling back and forth into the trough created by the boat. trimming out will make it worse.
one thought would be, are you stern heavy for some reason? maybe carrying water on board ya don't know ya have.
or i think stingrays really like some tabs of some sorts. smart or real. this will get your bow down some and help with porpoising. or maybe a 4 blade prop for some stern lift?
what's your wot? are you reaching or exceeding it with yer 19p prop.
i'd fix the prop at the very least if it's in question.