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Thread: Sudden high RPMs when trying to get on step

  1. #1

    Default Sudden high RPMs when trying to get on step

    My boat is in the shop. Maybe somebody has opinions on what the answer is to my problem. Mercruiser 5.7L engine, about 600 hours. Bravo 1 outdrive. Bayliner 2452 Classic. Here's what happened.

    Cochran Bay and tried to get on step, but boat just couldn't seem to make it and then rpms suddenly shot up. Tried again and same thing happened. Thought I had a spun prop so changed it out with my spare. Tried again to get on step and same thing. Tried one more time and rpms started to shoot up and I barely touched the outdrive trim button and suddenly things "caught hold" and got up on step. Rough seas, so had to slow down and ended up heading to Whittier at about 6-7 mph.

    Thought maybe engine coupler, or gear in outdrive, or clutch. Didn't smell any burning rubber (coupler). Mechanic took it out and it got right on step easily several times, so couldn't replicate the problem. I did take lots of weight off the boat before I took it in to him, and there was no extra fuel, cooler full of fish/ice, etc. that you'd normally have on the boat when using it.

    I'll talk to the mechanic more tomorrow, but during a call from him over the weekend when I had bad cell reception it sounded like -
    Not clutch - either a clutch works or it doesn't.
    Not coupler - either a coupler works or it doesn't.
    Wouldn't be gears in the outdrive - I asked him to go ahead anyway and at least check the top gear.
    Not a spun prop - he marked the prop and after running the boat the marks hadn't changed any.

    I'd rather he had said he found the problem and it'll take $X to fix than to tell me he couldn't find anything wrong.

    If he finds nothing wrong with the gears, my only guess is that it's a spun prop(s). He tested it with the second prop (spare) I'd put on. Maybe that spare was one that had spun before (although I don't see myself as having a bad prop as a spare but who knows). And if when I had it on and it finally "caught" before I had to slow down for the seas, then maybe with the light boat it never slipped for him.

    When I pick up the boat, I'll put on the first prop and give it a good run on the lake to see if I can get it to spin. If it doesn't, guess my only choice is to take the two props in to a prop shop and see if they can tell me if they are any good assuming there is a way to tell. Last choice is to buy two new props and hope for the best. Any suggestions?

    I just now called A-1 Prop. No testing for a spun prop but they said they can usually look at it and tell. Said it's possible that with a heavily loaded boat and too much power that the prop can cavitate and sound like a spun prop. I've never had this problem before and have often had the boat as heavily loaded or more heavily loaded.

  2. #2
    Member theultrarider's Avatar
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    My money is on a couple even with what you said. I had one years ago act very similar.

  3. #3
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    Maybe a humpback whale was screwing with you. Put a bubble net under your outdrive right as you were trying to go.

    It really does sound like a spun prop or a prop that was biting at air and not water.

  4. #4

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    Not at all sure, but it sounds like cavitation to me. I had the same thing happen suddenly a couple of weeks ago, stopped the boat, and found a small stick wedged onto the lower unit. It doesn't take much to disrupt the flow of water over the lower unit. Something similar could have caused your problem if you aren't able to reproduce it next time out. Hope you figure it out!
    "Miss Mary"
    Kingfisher 2725, twin Yamaha 150's

  5. #5

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    Quote Originally Posted by healerf18 View Post
    Not at all sure, but it sounds like cavitation to me. I had the same thing happen suddenly a couple of weeks ago, stopped the boat, and found a small stick wedged onto the lower unit. It doesn't take much to disrupt the flow of water over the lower unit. Something similar could have caused your problem if you aren't able to reproduce it next time out. Hope you figure it out!
    Had a similar problem with a stick that caught under my trim arm once. Was cruising at the time and stb prop began cavitating. Usually a sign that I pickrd up something on the drive. Typically I can just go to neutral then reverse her back and clear the debri but on this occasion it was a no go. Lifted the drive but could not find anything out of order that I could see. Figured the prop was breaking loose. I could get on step but could only make 20kts instead of the usual 29kts so I continued to my fishing hole we were close to. Later that day I got out my under water camera and found a small stick that hand managed to catch just right under the trim arm. Once removed the issue was gone. It's possible you had a similar problem. If you can't duplicate it agian I'd say it was just trash caught on the drive.

  6. #6

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    Could have been something like a stick. If you lifted the outdrive and missed it I suppose that might have happened to me.

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