Little RIB performance.

Discussion in 'Boat Design' started by corsair.p, Sep 15, 2007.

  1. corsair.p
    Joined: Jun 2006
    Posts: 23
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    Location: China

    corsair.p N.A.China

    Hi,gentlemen,
    We have troubles in testing our 12' RIB,the boat has too big trim angle when starting to planing.And even bad,when it's planing,always have porpoise movement make it very uncomfortable for people.
    We are thinking to add one more sprayrails each side(currently only have one) and add an outboard stabilizer on the 50hp OB to test again.
    But i am not sure it's gonna work,so if someone can give some idea to solve the problems we will very appriciate.
    Or maybe someone can tell me where i can find some technical informations to study?

    Thanks

    David
     
  2. lewisboats
    Joined: Oct 2002
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    Location: Iowa

    lewisboats Obsessed Member

    What horsepower is the boat rated for...50 hp seems way to high.

    Steve
     
  3. corsair.p
    Joined: Jun 2006
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    Location: China

    corsair.p N.A.China

    we just test the boat at it's Maxium Power as calculated from ISO standard.And it's 50hp.
     
  4. marshmat
    Joined: Apr 2005
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    Location: Ontario

    marshmat Senior Member

    I believe your problem is that the boat is way overpowered and thus way off balance.
    For comparison purposes, Zodiac's 340 DL and 380 DL (11'2" and 12'6" respectively) are rated for no more than 30 hp and 40 hp respectively; Zodiac advises against using more than 30 on either.
    A 50 hp outboard weighs about 100-120 kg. There will be a person sitting right in front of it, another 80 kg. So you have as much as 180-200 kg at the transom in a boat that is only twelve feet long. Couple that with a lot of thrust from a propeller down below the bottom and you have a recipe for excessive bowrise.
    I have two suggestions before you start gluing strakes and foils onto the thing.
    (1) Recheck the maximum power calculations.
    (2) Replace the 50 with a 30, move the crew forward a bit, and try again.
     

  5. corsair.p
    Joined: Jun 2006
    Posts: 23
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    Location: China

    corsair.p N.A.China

    Thanks,matt.We will try..
     
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