Best way to adjust trim?

Discussion in 'Stability' started by CapeCodAngler, Jul 14, 2009.

  1. CapeCodAngler
    Joined: Jan 2009
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    CapeCodAngler Junior Member

    I am restoring a 1978 19' Midland Skiff. We installed a 90 HP Four Stroke Honda and the boat sits back more than it should. (boat is rated to handle up to a 115 HP two stoke). I moved the gas tank and console forward, but still need more weight in the bow to level the boat. What is the best way to do this? Lead in the ballast?

    Suggestions would be appreciated.

  2. Stumble
    Joined: Oct 2008
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    Stumble Senior Member

    I am normally opposed to adding any dead weight to a boat for trim issues since it will decrease fuel efficiency from dragging around all the weight. On an outboard slightly adjusting the trime angle of the engine should solve this problem, but if it wont then I would look at a set of small trim tabs. Probably a set of fixed ones would work, though hydrolic ones offer more control.
  3. DaveJ
    Joined: Jun 2009
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    DaveJ Senior Member

  4. stimulous check
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    stimulous check Junior Member

    At speed the type of prop will also make a difference. A cleaver would help as it won't create the bow lift.
  5. TeddyDiver
    Joined: Dec 2007
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    TeddyDiver Gollywobbler

    At rest? If so reckon it's the 4stroke engine being more heavy than 2stroke 115's..
  6. Yellowjacket
    Joined: May 2009
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    Location: Landlocked...

    Yellowjacket Senior Member

    Since you have a lot more weight aft you obviously need more lift aft (assuming that you are talking about planing trim here). An afterplane (full width trim flap) set to be level with the current bottom will do the job nicely, you will gain both speed and efficiency if you are too nose high currently. A flap of up to a foot in length could be added to give you what you are looking for here.

    I would suggest that you model your current boat in a Savitski calculator (the one by Dingo Tweetie is find for what you are doingm and it is available right on this forum in the software area here is the link... Simply match what you have to the best of your ability in the spreadsheet and that will be a good starting place. Then add additional bottom length and move the cg forward the same amount as you added to the length and that should give you a very good idea as to how much it will do for you.

    This is the best thing you can do to solve your problem with the minimum impact on cost, efficiency and performance.
  7. pistnbroke
    Joined: Jan 2009
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    Location: Noosa.Australia where god kissed the earth.

    pistnbroke I try

    what we have not establiished from this guy is the actual problem

    Is it that its low in the water when stationary ..there is little you can do about that but build a motor well ....whats the transom height ?

    Is it a problem on the plane ....and so whats the problem ... motor should tucked right under when you hit the gas and then trim up once on the plane ...keep trim down in rough weather ....

    A 90- hp 2 st is 125 kg 50 kg lighter than a 4 stroke but thats only 1 light guy standing at the back hauling in a fish and a 115 2 st V4 is the sameweight as the 90 4 stroke ( yamaha quoted )

    More details please ...
    adding another foot to the back is an ugly idea that will not help at rest ....two boyancy chambers either side of the motor or side fitted pontoons can give more lift and have been used before and are in fact over the counter items in the USA...

  8. CapeCodAngler
    Joined: Jan 2009
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    CapeCodAngler Junior Member

    Thanks Gentlemen

    I took the easy way out and sold the boat. Thanks for your comments.
    1 person likes this.
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