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Thread: porpoising (?)

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    Have a 19 ft duckworth and recently changed it from an inboard to and outboard with a 225hp 4stroke motor. Took it out the other day and we started to porpoise really bad. Even trimming it out it would still want to porpoise. I guess my question is what are some causes of porpoising and how would I be able to fix it? Any ideas are greatly appreciated.

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    Member Frostbitten's Avatar
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    Quote Originally Posted by snowcrab24 View Post
    Have a 19 ft duckworth and recently changed it from an inboard to and outboard with a 225hp 4stroke motor. Took it out the other day and we started to porpoise really bad. Even trimming it out it would still want to porpoise. I guess my question is what are some causes of porpoising and how would I be able to fix it? Any ideas are greatly appreciated.
    Sounds like it might possibly be trimmed out too far to begin with.

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    Member patrickL's Avatar
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    Alot of times its weight distribution in the boat. Sounds like the weight of the motor hanging off the stern is the problem. A cheap fix is just to try a little ballast in the middle or further forward in the boat. Try moving gear or a person around to find where you need the weight. I routinely did this in the bush running an 18ft lund with a 40hp Etec when i was rinning empty. It would porpoise at high speeds but adding a little ballast up front would solve the problem. A better but more expensive solution is trim tabs. On my old 22 Ocean Pro if I ran full speed with the tabs up it would porpoise...add a little tab and it ran great.

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    You moved all the weight from inboard to outboard put weight back into the boat. Porpoising is caused buy the hull not being in the water, it rises as you come on plane to the point it doesn't have enough hull in the water then it falls back down keeps repeating till you slow down or change weight forward.

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    You probably need to lower your engine on the transom. Try going down one hole and if that doesn't do it, you may need go down further. Your engine's cavitation plate needs to be even or lower than the bottom of the boat.

    If your are porposing, trimming out the engine will generally make it worse. Start out with the engine all of the way down, which pushes the bow down. Then, you trim to lift the bow to get your untimate ride.

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    Member DRIFTER_016's Avatar
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    Quote Originally Posted by idakfisher View Post
    You probably need to lower your engine on the transom. Try going down one hole and if that doesn't do it, you may need go down further. Your engine's cavitation plate needs to be even or lower than the bottom of the boat.

    If your are porposing, trimming out the engine will generally make it worse. Start out with the engine all of the way down, which pushes the bow down. Then, you trim to lift the bow to get your untimate ride.
    Yep, as he says adjust your engine height to begin with.
    If you are still having issues with porpoising after motor height adjustment throw on a pair of these: http://www.cabelas.com/product/Boati...3Bcat104655780

    I guarantee they will fix the issue as well as giving you shorter times to get on plane, be able to stay on plane at slower speeds and they usually give an increase in fuel mileage. Everyone I know who has installed these on their boats raves about them.

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    Member pacific23's Avatar
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    Actually your Motor may be too low...
    On a transom mount motor your Cav plate should be FLUSH with the bottom of the hull.
    On a BRACKET, for every foot the motor is behind the transom the Cav plate should be on inch higher than the bottom of the hull.

    You may have to shift some weight forward to the bow locker.

    Your boat, if set up properly, should run fine without any trick parts [ I.E. trim tabs, dolphins, welded on parts or witch craft ]

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    Is the motor hanging from a bracket made to accept it, or is it mounted over the original transom ? A boat built to be an inboard may not have the correct angle at the transom to satisfy the trim of an outboard.

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    Member Grizzly Man's Avatar
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    I've got a 19" Advantage and I put a whale tail on it and that really helped out
    "What is it about a beautiful sunny afternoon, with the birds singing and the wind rustling through the leaves, that makes you want to get drunk?” --Jack Handy

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    Thanks for the info guys. Im going to try a few of these suggestions and hopefully something will take.

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    Member DRIFTER_016's Avatar
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    Lets us know how you make out and what worked.

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    I'm in the same situation. Can't decide between the whale tale and the smart tabs. Both are about the same money. I'm leaning toward the whale tale because I don't want the tabs on the boat while running my jet. Thoughts?

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    Member Akgramps's Avatar
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    To my understanding the whale tale is stricly for the jet and of no value if you have a tunnel.

    I am using a Permatrim on the prop and it works well, but I doubt it will solve the porposing issues, its a weight and balance thing.
    You need to get the bow down, either by rearranging the load inthe boat or by trimming the motor farther forward, did you look and see if the trim stop on the motor is adjustable?

    Some motors have a long bolt that limits the travel when the motor is trimmed in, if so it may have several posistions to choose from. Make sure its in the farthest forward posistion.

    Heres the permatrim: http://www.permatrims.com/

    They are well made aluminum units and work good, at least on my bost, good luck, John
    “Nothing worth doing is easy”
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    Trim stop is entirely removed. I'm not sure this is a good idea, but it's the only way I can run the prop and stay steady. If I trim it only a degree or two, it will start to porpoise. I suppose this is why I'm getting such good fuel mileage, but it's not very fun in heavy waves. I am POUNDING! Sure wish I could trim it down some to make the ride a little smoother when it's windy.

    Do you guys see any problem with the trim tabs and use with a JET? My stern tends to rise in hard turns, resulting in the occasional ventilation at the very worst time. I would have to have this worsened with trim tabs.

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    Member DRIFTER_016's Avatar
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    Quote Originally Posted by Orelk6x6 View Post
    Trim stop is entirely removed. I'm not sure this is a good idea, but it's the only way I can run the prop and stay steady. If I trim it only a degree or two, it will start to porpoise. I suppose this is why I'm getting such good fuel mileage, but it's not very fun in heavy waves. I am POUNDING! Sure wish I could trim it down some to make the ride a little smoother when it's windy.

    Do you guys see any problem with the trim tabs and use with a JET? My stern tends to rise in hard turns, resulting in the occasional ventilation at the very worst time. I would have to have this worsened with trim tabs.
    You can pull the top mounting pin on the smart tabs and set the top mount to it's highest (softest/least amount of downforce) when running the jet and reset lower when running the prop. Heck you could even make a short solid rod (to replace the shock) to completely raise the tab out of the way for that matter.


    Here's a crappy diagram to show what I mean.

    Tabs.jpg

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    Well, maybe I should try the Smart Tabs.

    The Wooldridge boats have an extension on the stern that allows you to bend it up or down to help trim the boat. With the Smart Tabs, I should be able to maximize my jet performance with the hull extension adjusted to keep the arse DOWN, and allow the Smart Tabs to compensate when the prop is on.

    I guess it's worth a try? What could go wrong, right?

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