Cannot get boat onto plane??

Discussion in 'Outboards' started by dawzo, Mar 5, 2013.

  1. dawzo
    Joined: Mar 2013
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    Location: newcastle australia

    dawzo Junior Member


    I have recently purchased a 4.3m American sea strike fitted with a yamaha 1995 85cv
    Im honestly not relly than onto it when it comes to outboards and hulls on the technical side of things, So i will pass on what i was told and leave it to your opinions.

    I was told as the sea strike is an american hull it was not designed for a yamaha motor, so the transom angle is wrong and a set of wedges would get the motor in the right position.
    On the water the boat will come up onto the plane no dramas at all, but as soon as its came up it nose dives straight away and pushed the bow into the water. i can trim the motor out all the way untill it cavatates and it makes no difference at all.

    At about just under half throttle it will kind of plane nicely but if i accelerate any further straight into the water it goes. I went to purchase wedges and was told they wouldnt do anything! the motor had to be lower.
    Ive added wedges, and lowered the motor to the top hole and still no difference, - Honestly its worse.
    So far i have tried
    - Lifting the motor as high as i can get it- lots of cavitation, not any better.
    - using the hole 2nd from the top. can almost plane in slow conditions but burys when accelerating
    lowering the motor to the top hole and adding wedges - still burys the bow.
    I have run a string line down the center of the hull so you can see there the cav plate sits in relation to the bottom of the hull, one photo with it trimmed right in, one with it trimmed out a little,
    Any thoughts would be awesome.

    Cheers Matt
  2. dawzo
    Joined: Mar 2013
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    Location: newcastle australia

    dawzo Junior Member

    I have also been advised the Hull may have a '' hook '' in it.

    I will also add a few pics of the back of the hull i have taken with a straight edge.

    The Starboard side towards the transome has about 5mm's where it '' sinks in, where the port side has the same, about the same depth, but with a large buldge poking out about 1m in about 5mm high.

    Ill add the pics so its clear what i mean
  3. dawzo
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    dawzo Junior Member

    engine trimmed right in.jpg

    first Pic with the motor trimmed right in. - To me it looks way too low, but as soon as i trim it out a little I think it looks great.

    - having said that, Thats my opinion and i dont really know
  4. dawzo
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    Location: newcastle australia

    dawzo Junior Member


    Hopefully this Pic works.

    As you can see on this second Pic, with the motor trimmed out a little the string line is sitting on the cav plate.
  5. tom28571
    Joined: Dec 2001
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    tom28571 Senior Member

    Can't tell much from the photo or explanation other than you have received some bad advice. All outboards have essentially the same mounting configuration, including Yamahas.
  6. dawzo
    Joined: Mar 2013
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    dawzo Junior Member

    This is What MAY be a hook.
    This is the starboard side. one end of that angle sitting on the bottom of the boat right at the transom. as you can see the angle is just over 1meter long, and there is quite a gap just over that distance.

    Starboard side
    hook in star side.jpg

    This is the Port side, angle in the same spot,

    port side hook.jpg

    Any help would be definatly appreciated.
  7. dawzo
    Joined: Mar 2013
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    Location: newcastle australia

    dawzo Junior Member

    Thanks Tom.
    You are right, definatly seems I have been given some bad advice.

    - not sure how visable the orange string line is, But u have that running along the bottom of the boat in a straight line.
  8. CDK
    Joined: Aug 2007
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    Location: Adriatic sea

    CDK retired engineer

    In the picture of post #3 the engine is a bit low and trimmed too far in. Put the pin in the middle hole, that should make things better.
    If the boat still goes nose down when planing, there must be something wrong with the weight distribution, like water under the floor moving forward when the boat is in horizontal position.
  9. daiquiri
    Joined: May 2004
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    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    Yes, that is a hook. And it will definitely want to pitch your bow down.

    It looks like the boat was made (or modified?) for a larger outboard motor. In that case the hook might be there to carry the weight of the large OB, help it get on plane and trim down the boat at high speeds. With a smaller OB (talking about a difference of some 50 kg, 110 lb, hanging from the transom), above a certain speed the hook starts giving too much lift for a weight of a smaller OB, and digs the bow in the water.

    Possible solutions (in order of increasing cost):
    - shift the weights (console, items, ballast) aft;
    - sell this motor and get a bigger one;
    - get rid of the hook and eventually install the trim tabs.

  10. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Take some foam sheet material, from the local big box store and use a spray mount adhesive to glue it to the underside of the boat, temporary. Next using a long board, sand the foam, so the hook areas on each side of the centerline are filled in and made dead flat. Clean the surrounding hull area good, then apply a layer of duct tape over the foam, effectively taping it to the hull. Now place the ventilation plate at the bottom of the hull on the centerline, no lower then take her for a ride. With the hook removed, she'll probably run out just fine.

    You'll probably need to play with pin holes, but this is easy enough. Once you discover the hook is causing your problems, you can remove the hook with 'glass and filler. The foam and tape will just tell you it's the hook, which might be designed in or more likely it's from a poorly fitted trailer.
  11. Yellowjacket
    Joined: May 2009
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    Location: Landlocked...

    Yellowjacket Senior Member

    Also make sure the stringers are sound. You most definately have some hook, and you need to address that, but you also need to make sure the hull isn't flexing more (and giving you more hook) when it is loaded by the planing forces. The amount of hook you have will cause it to plow, but it should plane ok with that much hook. If it's plowing as soon as it planes off you may well be getting more hook if the hull isn't sound.

    If you can pull up the flooring in the area near where the hook is, or look under the floor when you are undeway you may well see that the amount of hook is increasing when you are planing, and giving you even more hook than what you are seeing under the hull when it is on the trailer.

    A friend had a boat that had broken stringers and it would plane ok, but as you went to higher speed it plowed like crazy. There wasn't much hook visible on the trailer, but the cracked stringers allowed the bottom to distort and the hook got much bigger when it was planing...

    If the stringers aren't sound just filling the hook you see now won't help much.
  12. Submarine Tom

    Submarine Tom Previous Member

    "Cannot get boat onto plane??"

    I think you're going to need a bigger plane.
  13. boatbuilder41
    Joined: Feb 2013
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    boatbuilder41 Senior Member

    Yellow jacket is right. I can tell this guy knows boats. Im new here and i dont know him but i been building boats all my life. Im happy to know there is some people in my line of work that really knows about a boat. Most are just full of B.S.
  14. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    He's likely a smart guy, but you did not need much grey matter to figure out what the problem was here, imo. :p

  15. tunnels

    tunnels Previous Member

    ok the panels each side have hook !!what about the keel ?? has it got hook as well ??
    If the transom angle is wrong then wedge the motor !!!
    as for height sound like you really dont know what your doing !!!
    its reall simple the under side of the plate above the prop should be just a couple of mm above the hull bottom !!
    raising the motor is completely the wrong thing to do if anything you should have gone down not up !!! try and load the boat heavy right at the back !!!The hook is acting like a trim tab raising the back and pushing the nose down !!!!
    So how do you intend to get the hook out of the hull ?? filling it up with a few kilo grams of bog or doing the repairs from inside the hull and pushing the panels back out ,because thats where the problem really is inside needs pushing back out level again . rollers in the wrong place on a trailer will do that real easy and you never even notice it !!!!

    Any 85 motor yamaha , omc or merc hasnt got the guts to do anything to get the nose up after its gone down so it will plane and keep it planeing !! double the hp and then your talking

    And just because its and American hull doesnt make it any better that any other boat if anything it possibly why its like it is !!! :p
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