Results 1 to 11 of 11

Thread: porpoising (?)

  1. #1
    Member
    Join Date
    Mar 2009
    Location
    Wasilla
    Posts
    117

    Default porpoising (?)

    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.

  2. #2
    Member pacific23's Avatar
    Join Date
    Dec 2010
    Location
    Whitesboro, Texas
    Posts
    534

    Default

    Most causes of porpoising are running to much pitch of prop, weight distribution, and motor mounted to low.

  3. #3
    Member SkinnyRaven's Avatar
    Join Date
    Feb 2007
    Location
    Anchorage
    Posts
    320

    Default

    Raise the mount and retest.

    07 Ocean Pro 220 ET HT
    115 Yamaha
    Garmin 740S, GMR 18 HD
    Airmar TM 260-MM

  4. #4
    Moderator stid2677's Avatar
    Join Date
    Apr 2006
    Location
    Fairbanks Area
    Posts
    7,274

    Default

    Everything they already stated, but adding a hydrofoil fin helps dramatically with porpoising and hole shot.

    One like this

    http://www.amazon.com/Sporttec-Sport.../dp/B000ZFTKUG
    "I refuse to let the things I can't do stop me from doing the things I can"
    Founding Member
    http://www.residenthuntersofalaska.org/

  5. #5

    Default

    I second the SE Sport hydrofoil...will improve your holeshot and give you more trim leverage and also lift the rear of the boat at cruise. Keep the bow down and it won`t porpoise. Mine is incredible on my boat it makes the trim very touchy. Have someone look at your cavitation plate while doing 30mph and see if it is in the water or on the surface...if under move the engine up as noted above.


    Heavy Hitter Fishing
    https://www.facebook.com/pages/Heavy...54441957966186

    Kodiak Custom Fishing Tackle Pro-Staff


  6. #6
    Member
    Join Date
    Feb 2007
    Location
    Los Anchorage
    Posts
    481

    Default

    I buddies of mine boat did the same thing. He had some trim tabs put on the boat and worked like a champ.

  7. #7
    Member
    Join Date
    Mar 2009
    Location
    Petersburg, Ak
    Posts
    114

    Default

    First, I noticed you said "trimming it out didn't help," trimming out would make a porpoise worse, to keep your bow down stay trimmed down. Second, a lot of boats have an inch or two of the bottom extend past the transom, if that is bent up slightly it will cause the bow to raise, you can bend that down to help keep the bow down. Those things in addition to the other tips mentioned above may help your situation.
    Casey
    Yamaha Dealer
    Petersburg, AK

  8. #8
    Member akblackdawg's Avatar
    Join Date
    Aug 2009
    Location
    Wasilla
    Posts
    1,456

    Default

    Porporsing is a common problem when setting up airboats. Remidy should be the same. Cause of your problem is moving the weight to the rear more then it was when you had the inboard. One easy fix on a aluminum boat. On the rear transome you will see a lip from the bottom going across where the transom is welded onto the bottom, it will protrude about 1/2 inch back. If you take a big hammer, and go across this lip, rapping on it hard, it will bend down the lip slightly, don't worry you won't hurt anything. The amount that is bent down is minimal, but enough to produce a little more drag at the transome, simular to a trim tab. This will cause the rear to lift slightly thus forcing down the bow. If you transome is painted and you don't want to scratch it up with hammer blows, use a metal block to hit against with the hammer. This really works except in extream situations. If the first time doesn't do it, do it again with a 2nd treatment. It will not damage your boat. There are other things you can do, such as movig your fuel tank forward, moving batteries forward, and any other major weight you carry. But the easiest and most perminant is by bending down that lip a tad. I had to do it to my new boat, no problem. Bud
    Wasilla

  9. #9
    Member
    Join Date
    Feb 2011
    Posts
    1,959

    Default

    You stated that you changed from a inboard to a outboard. If you mounted a outboard on a stinger type mount you can have a real hard time getting you boat not to porpoise. The only way I could stop porpoising on one boat was to change from a stinger mount to a full hull extension type mount. If you have any questions you can PM me.
    Best of luck

  10. #10
    Member
    Join Date
    Mar 2010
    Location
    Anchorage
    Posts
    19

    Default

    I had that same problem real bad with my 20 ft wooldridge and as akfish1 had mentioned, there is an extended piece in the back of the boat that needed to be bent down (level with the bottom of the hull). Now, I have tried the hydrofoil first and it made no difference. It wasn't until I bent the tabs down, after that it completely went away (even when I trim up). If you don't have the tab, maybe trim tabs can be an option?

  11. #11
    Member Gundog's Avatar
    Join Date
    Apr 2007
    Location
    1250 miles S/O paradise in the lwr 48 dreaming of SE AK
    Posts
    255

    Default

    Porpoising = The lack of enough of the hull in contact with the water to make a planning surface. It helps to understand what is happening the hull is lifting and falling off a portion of the hull and lacking a large enough area to plane on. There are several things that can cause this motor height is one a hull with no flat running area is another. Many of the things discussed are designed to fix the symptom such as bending the tab adding trim tabs hydro foil Etc. Another thing that can be done is adding lifting strakes. I would start with a strait edge on the hull bottom to see if you have a rocker in the hull. Improperly loaded or overloaded boat can cause this. Good luck I had this problem with a boat I owned and this is the info I learned after months of trying to figure out what to do. In my case a floatation pod on the offshore bracket did the trick it gave me enough flat area for the hull to ride on while on plane. This seems to be an issue more often with boats under 22' and lower HP applications 150 HP and lower.

    Mike

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •