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Thread: Bumpy ride

  1. #1

    Default Bumpy ride

    My 21foot Hewes Craft River runner is porpoising (sp) like crazy if I get above about 4900 RPM. It just started this last week when we were dipnetting. Not sure if it was the load distribution or if something is out of whack (technical term). The jet seems to be running fine. Anyone have any ideas?

  2. #2
    Moderator stid2677's Avatar
    Join Date
    Apr 2006
    Fairbanks Area

    Default Trim???

    Did the trim switch get bumped. In my experiance, trim or load is about the only thing that I have found that will cause that. You did say you were dipping, a boat load of reds can weight more than you think. 5 to 7 lb average times how many fish.


  3. #3
    Member broncoformudv's Avatar
    Join Date
    Apr 2006
    Anchorage, Alaska


    I will have to second what stid2677 said. The load is usually the culprit of a boat porpoising when it has never done it before. A load of reds can weigh a lot. Did you have most of your weight towards the stern?

  4. #4


    I couldn't find the trim tab so it may be gone. And all the weight was in the rear, to include two big bubbas and one smaller one. I'll have to get her out again and try it with the load different. Gives me a good excuse to tell the wife I need to go chase Silvers at Seward >

  5. #5
    Member AKBassking's Avatar
    Join Date
    Oct 2006
    SE Alaska-Summer Columbia River-Winter


    I have trim on my engine and I find the more I trim it "up", I start to porpoise. If I am in rough water just trimming a little will push the nose over and I start to feel like I am on a roller coaster ride. It also causes the jet to catch a little air.

    1988 M/Y Camargue YachtFisher
    MMSI# 338131469

  6. #6
    Join Date
    Apr 2006

    Default another option

    I run a 20' hewes Sea Runner 115hp yamaha... I'm sure load placement has a lot to do with the ride but my boat had a similar issue. I installed a Stingray Hydrofoil... It did not cure the problem but helped tremendously.

    I can still suffer from the "roller coaster" if I trim up too much but I've found it to be much less frequent. It also helps hold the boat on step at lower RPM's.

    I've read Doel-fin is a good Hydro foil as well.

    Here's a link from a Hydrofoil discussion earlier this year.

    Hope this helps.. Winmag

  7. #7


    Check the bottom of the boat and the very end and make sure the band that extends the bottom past the transom is straight and not bent up. Sometimes that band will push up from the boat bouncing on rocks while it is tied up.


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