New Boat Porpoising

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

  1. powerabout
    Joined: Nov 2007
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    powerabout Senior Member

    IMHO you have driven too many consumer dogs that are made to be safe hence you can trim the engine till the prop slips but the hull is designed to jam the nose down and it will never porpoise.
    You can always tell as if they go faster with the engine trimmed past parallel with the water surface they are stuggling to get to nose up because driving the gearcase through the water on a tilted angle is not fast

    How about a vid of this hull so we can all see what this boat does?
     
  2. keysdisease
    Joined: Mar 2006
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    Location: South Florida USA

    keysdisease Senior Member

    80's vintage Seacraft, Contender, my father in law has an Intrepid. All South Florida Boats where we boat hard year round, fish in the middle of the gulfstream and sometimes run to Bimini for Lunch. I'm a noob

    Steve



     
  3. Frosty

    Frosty Previous Member

    Its not uncommon to see boats driven without proper trim. Its not uncommon to see bad driving on the road. Many just don't seem to get it.
     
  4. wheelybin
    Joined: Aug 2011
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    Location: Australia

    wheelybin Junior Member

    Hi To All, Have been Away,
    You have hit the nail on the head their, The boat dealer and company rep have both said to me, This has got them stumped a bit, and has been a challenge for them, what they have done is fit a 60 hp Merc EFI, they tell me that it will not under power it, l can only go on their word until l drive it for my self, If l am not happy with the outcome, they have two options Money Back or new boat, Thats it, l do beleave that l am being very patience with them, But time is running out for them.

    Regards Andrew.
     
  5. keysdisease
    Joined: Mar 2006
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    keysdisease Senior Member

    Sounds fair Andrew, but be sure you have the boat loaded as you will use it. The boat may perform OK with you and a salesman aboard but you need it to perform with your family, friends and a cooler of beverages aboard.

    Steve


     
  6. wheelybin
    Joined: Aug 2011
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    Location: Australia

    wheelybin Junior Member

    Hi,
    When l get the boat back, l will film it if it purposing and post it for everybody to see, In theory, Should have filmed it, then posted it, for every body to see. what l am talking about.

    Regards Andrew.
     
  7. Frosty

    Frosty Previous Member

    That would be a good idea. Ive been biting my lip at wanting to say that 60 HP is tiny. I would want at least twice that. There I said it.
    You will have difficulty pulling one skiier with 60HP.


    Next time you go out with your 100Kg frame ( same as me exactly, well 99.9) walk about the boat try at the back and at the front.

    If the boat is hooked it will respond in the strangest of ways.

    Cant wait for the VDO.
     
  8. wheelybin
    Joined: Aug 2011
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    Location: Australia

    wheelybin Junior Member

    Hi Frosty,
    Me and my 100kg frame, do appreciate your comments, these are the little idears that l am after, so that l can check, l hope that the 60 hp is not going to under power her. will be in touch soon.

    Cheers Andrew.
     
  9. Submarine Tom

    Submarine Tom Previous Member

    Andrew,

    If your boat is purposing, then it sounds determined.

    Now if it's porpoising, that's a whole different matter.

    -Tom
     
  10. pistnbroke
    Joined: Jan 2009
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    Location: Noosa.Australia where god kissed the earth.

    pistnbroke I try

    if its only 4400 at WOT then it sounds like you need to drop the pitch about 4 inches ....having a small motor means you need to run it harder and then its noisy more fuel consumption too.....it all sounds like a balance problem to me and constrant trimming may be required more on some boats than others ...wake ahead ..trim down a little ...turn ahead ..trim down ..straight run trim up a little ..going over the bar ..full down trim ....just depends on how tuned the boat is to max performance....why dont your salesmen take you out in another boat of same similar model with one of there other customers ...Agree with frosty ...motor too small wants a 90 hp
     
  11. wheelybin
    Joined: Aug 2011
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    wheelybin Junior Member

    Hi Frosty,
    Just thinking, what you said, May l please ask you, could you list some of the strange response l might get. thanks

    Have spoken with the dealer today, They are happy with the way it has gone with the new 60 hp motor, They are getting another company Rep to give his appinion on situation. And go from there. They have said that they were concerned that the boat was a bit slow to get out of the water, they have dropped the motor one more hole & put a different prop on it, It will probably be even slower coming out of the water, when we have two bisects being towed behind it, This is their last chance.

    Regards Andrew.
     
  12. Frosty

    Frosty Previous Member

    Hooked boat will cause porpoising, chine walking, poor cornering, chine flopping, poor trim response. Google it.

    The bottom of the boat should be flat, if its hooked it is higher in the middle that it is at the bow and stern. This can cause the boat to stick to the water and literally pop up off it, releasing itself from the suction. This suction can make all sorts of handling probs as you can imagine.

    All you have to do is get on your hands and knees at the back of the boat and with one eye look down the hull of the boat. The trailer gets in the way most times but a straight edge of some sort.

    Im a little confused at this story to be honest if its porpoising then they should know that and know what to do. It seems from where Im sitting they are trying to improve it to a state that you will accept.

    Yes a 60 will have difficulty coming up on the plane and with you and some more, it may not at all.

    Dropping the engine does not help it out of the hole unless its cavitating, normally it will break free and cavitate just as it has got out of the hole.

    Your getting deeper and deeper in a mess here.

    Ive never heard a boat shop having so much trouble with a little boat. If you get the chance to drop it and get your money back I would, and start again with another boat shop.
     
  13. tunnels

    tunnels Previous Member

    ok
    Fitting a outboard to any sort of power boat hull !!
    The cavitation plate underside should be about 5 mm above the bottom of the level of the hulll !!
    Lay a long straight edge on the hull not the keel and check !!.
    An outboard the size you are referring to will have power trim Yes ??
    While the straight edge is along the bottom of the hull check the trim and adjust the motor trim ina and out till the plate on the motor is paralell with the straight edge . That is your starting point . WHEN YOU HAVE ACHIEVED THOSE THINGS PUT THE BOAT BACK IN THE WATER .
    Get the boat going at a comfortabel speed just on the plane with the motor and the trim tucked right in !!
    Dont touch the throttle but listen to the sound of the motor !!and watch the needle on your tacho Most important !!!
    Slowly work the trim button little by little till the boat starts to come alive !! The sound of the motor will change and the needle on the tacho will come up a few rpms all by its self , Watch the spray out the chine it will gradually move back and at that point the boat should pick up speed all by its self just by trimming the motor without touching the throttle .
    When its reach it optimum trim if you move the trim a little further it will start to Porpose !!!
    Back the trim down to where it was when it felt good !!!. Take particular note where it is on you trim gauge !! Thats where it should be for the way that boat is set up !!!!.
    Each time you use the boat repeat what i have just told you . Small boats change with the way it loaded and where people are seated . if some one moves to a differant place the trim changes if you move tanks etc the trim changes . There nothing magic about it its just common sense . Porposing is a boat out of trim and balance . We are alway in to much of a hurry and never listen to what the boat is telling us . Each boat is differant to the next even if they are the same sort and modle they are all individuals . :D

    Rocker in a hull also can cause porposing but if you load the boat slightly tail heavy you can use the power trim to sort that . Be gentle with the power trim !!!! ,Use it little at a time not hold your finger on and go up and down all the time .
    Its a fine adjustment between porposing and not porposing . Take your time and get the feel !!!!
    become one with your boat know what it likes and dosent like , understand it !!! or you will continually be fighting with it forever !!.

    Rocker is introduced in fast boats to get the hull up and going very quickly so it rides on the cushion of air beneith the hull with just the last few inchs of the transom/keel touching the water .
     
  14. tunnels

    tunnels Previous Member

    Hi
    I see that the havent been anymore posts on this sight , How did the re-setup go ??
    Did you get what i was saying ??
    I hope its fixed and going well !
    Take care and get lots a time behind the wheel and become one with the machine !!
    Bye :p
     

  15. Easy Rider
    Joined: Oct 2009
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    Location: NW Washington State USA

    Easy Rider Senior Member

    I'm curious how this all turned out too. I've got an 1977 18' Winner w 60hp Suzuki (much the same I think) and I don't ever recall the boat porpoising. I'm guessing it was water in the hull but would like to find out.
     
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