New Boat Porpoising

Discussion in 'Powerboats' started by wheelybin, Aug 7, 2011.

  1. tunnels

    tunnels Previous Member

    Some people get in a boat and get carried away pushing the trim button up and down without thinking , when it dosent work and wont trim the boat properly they blame the boat, always the boat !!
    small boats as so easy to upset the trim just by moving thing inside or people sitting where they shouldnt again without thinking . do the basics watch and listen 99% or the time it works . trim slowly till you get it right and remeber where ot is and dont jab the buttom up and down all the time . :D Water in the hull is nearly always in the back only !!and it dosent move about that much !
     
  2. Easy Rider
    Joined: Oct 2009
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    Location: NW Washington State USA

    Easy Rider Senior Member

    Both my 16' aluminum skiff and my 18' FG OB have power trim and neither boat is sensitive to porpoising. If I have the 18' w 60 Suzuki adjusted for normal trim (a bit up) I need to put it all the way down to do very sharp turns or it will cavitate. But no porpoising.
     
  3. tunnels

    tunnels Previous Member

    IF YOU HAVE CAVATATION IN SHARP TURNS , MOTOR IS TRIMED TO HI SHOULD NEVER HAVE TO TRIM ALL WAY IN!! , DOES IT CAVITATE ONE SIDE BUT NOT THE OTHER IN A SHARP TURN ?
    tHE DIRRERANCE IF 1/4 OF A INCH MAKES ALL THE DIFFERANCE WITH ENGINE HEIGHT ON THE TRANSOM !!:D
    MOST MOTORS WILL CAVITATE ONE SIDE MORE THAN THE OTHER BECAUSE OF PROP ROTATION , THE AIR GETS SUCKED DOWN THE SIDE OF THE GEARCASE AND AIRATES THE PROP BY LOWERING THE MOTOR ON THE TRANSOM JUST 5 MM CAN AND DOES SOMETIMES STOP IT FROM HAPPENING BUT HOW MANY TIMMES DO YOU NEED TO LOCK THE MOTOR ROUND ON SUCH A ANGLE ?? ONCE EVERY BLUE MOON ?? .
     
  4. Mr Efficiency
    Joined: Oct 2010
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    Location: Australia

    Mr Efficiency Senior Member

    Wheelybin gone into smoke, for some reason. Be nice if he could report how it panned out.
     
  5. tunnels

    tunnels Previous Member

    No news is some times good news !,
    silence is golden !,
    never wake a sleeping dog thats wearing a chain !. :eek:
    Maybe he forgot his way home ??
    Or the wife said pack your boat and go ?? and he went !!
     
  6. Jimboat
    Joined: Feb 2002
    Posts: 261
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    Location: Canada

    Jimboat Senior Member


    wheelybin - Porpoising is pretty common...any vee hull (or tunnel hull) can be susceptible to porpoising, depending on design and setup. Flatter bottom vees are more prone to porpoising than steeper deadrise vee hulls, but there are several contributors to the occurance and any hull can find the problem caused by dynamic instability.

    The "bouncing" or porpoising comes from a rapid change in the location of the center of Lift as the boat accelerates. The relocation of static weights is one way of dampening the rate of change of the CofL...so it's not always obvious whether to move weight fore or aft in order to cause the "dampening". The solution can be calculated, but it's also not too difficult for you to find out through testing, whether moving weight fore or aft will help your particular problem.

    The resolution to a porpoising problem with a hull design is most always addressed by causing the boat to run with less trim. There are many different ways of achieving this.

    Porpoising is a function of the lift generated by your hull, the deadrise of your running surfaces, and the trim angle that is needed to get that lift. The onset of porpoising is, in part, influenced by the weight balance in the boat. Altering the deadweights in your boat (fuel, payloads, etc) can affect the speed and trim angle that porpoising will initiate. If a boat is porpoising at a given speed and load, lowering the trim angle will reduce or eliminate the porpoising. There are several ways to get there, but the bottom line is to reduce trim at the velocity of porpoising onset. (Higher deadrise hulls are less suseptible to porpoising.) Even if the hull design is operating in the "Porpoising Regime" through a full range of velocities, reducing trim in some way will improve or resolve the problem.

    For your hull design and setup, the speed and trim angle at which you will see the onset of porpoising can be determined. Changing trim angle, changing motor height, changing propellers, moving weight foreward, will all help to reduce porpoising at a given velocity. Changing design variables such as running surfaces design, deadrise, engine setback, etc. can help maintain the hull in stable planing regime, avoiding porpoise regime.

    Trim tabs (or more extreme whale fins) will also improve a porpoising problem, but these will also affect overall performance of the hull. Adding transom wedges can often help too, since they will allow for more negative trim travel, if it's required. Raising the prop shaft higher will shift CofG foreward and reduce trim angle. More HP also reduces trim angle. Reducing your trim angle in some way will always help a porpoising problem.

    Have a look at this article on "Hump Zone/Why does my Boat Porpoise?". It may be of some help to understand the problem.
     
    1 person likes this.
  7. Easy Rider
    Joined: Oct 2009
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    Location: NW Washington State USA

    Easy Rider Senior Member

    Tunnels,
    Yes. It seems it's too high but I mounted the cavitation plate 1" below the bottom of the boat and the boat is a deep V without a keel. Now the holes are in the transom and there's no adjustment down. My bad. I would need to cut out some of the bracket to lower it and that would only be a small amount. I like to run my engine tilted up a bit but it has'nt been a problem yet. I have bigger problems w the boat to address.
     
  8. pistnbroke
    Joined: Jan 2009
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    Location: Noosa.Australia where god kissed the earth.

    pistnbroke I try

    usual thing wheelybin gone missing ..last thing was a 60 hp motor fitted but no report n results ....SSDD as they say .. On to more important things
    WHERE IS FROSTY .....
     
  9. IMP-ish
    Joined: Jan 2011
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    Location: united states of america

    IMP-ish powerboater

    My guess is they finally got wheelybin all set and he's out enjoying his boat :D

    Wish people would post a followup though to let us know what the result was.
     
  10. tunnels

    tunnels Previous Member

    Yeah i know what you mean . But if it didnt work you'd have heard all about it !!:eek:
     
  11. wheelybin
    Joined: Aug 2011
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    Location: Australia

    wheelybin Junior Member

    Hi every body, l'm back
    Sorry that it has taken me so long to reply, l work in the mines, home now, Well just to let you know, they have come to the party after l gave them 3 choices 1/ fix the boat 2/ give me new boat 3/ give my money back, they came back to me with an free up grade to the Signature 493 F 2011 model, l took up the option to go to a bigger motor 90 hp Merc opacity-max (had 75 hp Merc) and they have taken my traveler 157 back with all the trimmings, They Haines Group will do all my transit covers and over night cover in the factory, New trailer, new Compass, dual battery's, lights.
    Should have the new boat in 2 weeks time, delivered to my door.

    l Have taken some photos of my old boat, will post soon, when new boat arrive will post photos of that,

    As for the problem, the 157 left Melbourne to day 22 September 2011, to go back to QLD on a truck, They will do some testing to see if they can find issue, then crush they tell me.

    At this stag l would like to thank every body so much that has made comments, l don't think that l would be where l am now, with out your most valuable in put, So thank you Again

    as a result of this l have come out of this with a $6000-$7000.00 free up grade from a traveler boat to a signature boat.

    very Best Regards

    Wheelybin.


    P.s Have lost some weight.
     
    1 person likes this.
  12. pistnbroke
    Joined: Jan 2009
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    Location: Noosa.Australia where god kissed the earth.

    pistnbroke I try

    great result ..last boat I shipped out of queensland ( 16 ft ) they picked it up on a forklift trailer and all and dropped it on the outboard ripping out the transom.....no worries not mine I had sold it and got paid ....good luck with the new boat and we await the pictures .
     
  13. Landlubber
    Joined: Jun 2007
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    Location: Brisbane

    Landlubber Senior Member

    Thank you Haines, nice work fellas.....I can just imagine Chinese made manufacturers doing that eh....in ya dreams.

    Buy Aussie made and trusted like Cruise Craft, Haines etc and at least you are dealing with local families that KNOW boats and why they make them. Others are just making gadgets to get some money, have no idea how to fix anything or even why subtle changes make all the difference.
     
  14. wheelybin
    Joined: Aug 2011
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    Location: Australia

    wheelybin Junior Member

    Hi Pistnbroke,
    It is a good result, l am so keen to get the new boat and go cruising, Cant wait, l must say that l think that l have been so lucky that they did not just wipe me, like you here with so many car company's do, that you see on the TV.

    Both the Boat dealer and Haines company rep have been great, other then them trying to pull the wool over my eyes just a bit, after joining the boat forum and firing question after question at them l was not about to go away, Hence the offer of a bigger boat at no cost. l'm Happy

    Best Regards
    Wheelybin.
     

  15. tunnels

    tunnels Previous Member

    News is all good !!
    What mine do you work in ?? :D
     
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