Chine and stability

Discussion in 'Stability' started by crowsridge, Mar 24, 2012.

  1. crowsridge
    Joined: Apr 2010
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    crowsridge Senior Member

    Hello,

    So, my sons want a boat. Smaller sled, 15'. Jet.

    I want to have a very stable boat, but Im seeing conflicting info. One builder says a round chine is best. Then I see a sharp chine and still another reverse chine.

    I lean towards the reverse chine but would love youre educated input.

    Thanks,

    Chris
     
  2. Petros
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    Petros Senior Member

    Do not shop for a boat based on hard chine/round bilge thinking one is more stable over the other. You were misinformed. The design of the hull/cg height and other factors has more effect on stablity than hard chine or round bilge. You can get a bit more stablity with hard chines of identical hulls, but no two brands are identical, other factors have FAR more influence than chine/no chine. A good designer can make a hard chine hull behave identical to a round bilge one by trading off other design features.

    Usually a fast planing hull will come up on plan much faster with hard chines, and that is why there are used. If you are getting a heavy and slow boat, you will never come up on plane so rounded hull forms will have less drag. Primary stablity is what the designer choose, no matter the hull form they might use based on ability to plane and/or construction method.

    It really depends on your intended use and how much you want to compromise any or all of your desired performance ideals. Best to go try as many out at a local on-water boat show to get a better feel for how they behave.

    Buy based on the performance/bahavior you want, not on hard chine vs. round bilge.

    Good luck.
     
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  3. crowsridge
    Joined: Apr 2010
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    crowsridge Senior Member

    Sorry, I left out a part of info I see. I am looking at plans for building this boat.

    One build i saw here was a sheet of aluminum that was formed with a roller and break. First stage looked like a flat bottomed U then capped the stern and curved the bow up and towards the center. He claimed the wide roumd chine made it stable.

    A garvey style is a harder edge and the the Boston Whaler style have reverse chine. Sorry, I never think of just buying a boat any more:D
     
  4. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    The guy making the suggestion that the rolled chines, make his boat more stable is talking out his butt. A rolled chine or round bilge hull form, doesn't have any significant advantage or disadvantage in the stability department (all things being equal). Stability is considerably more complex then this, but boiled down to layman's terms, is purely a function of beam and weight location.

    A round bilge or rolled chine hull may be more "tender" initially, but only if the WL beam is decreased as a result of the bilge turn shape, in comparison to a hard chine form of similar dimensions. This isn't comparing apples to apples, so a moot consideration.

    The same would be true of a "reversed" chine, which I'll assume is a down turned lifting strake along the chine. Hydrodynamics and flow dynamics are pretty complicated subjects, which leads one to believe the aluminum builder is speaking about things, he clearly doesn't understand.
     
  5. crowsridge
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    crowsridge Senior Member

    That makes sense. If it were better, the big boys would be doing it and saving all the weld and fab time of seperate parts and pieces.
     
  6. PAR
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    PAR Yacht Designer/Builder

    What plans are your interested in?
     
  7. crowsridge
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    crowsridge Senior Member

    I have a set already for the Glenn L Rogue Runner 20' version. Buy its more narrow than Id like. Bateau has the Garveys, but they lack style in my opinion. Still looking..........
     
  8. messabout
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    messabout Senior Member

    Crowsridge; why do you believe the Glen L boat is too narrow? Does your boat have a special application, requiring excess width, that you have not mentioned yet? How much power will you use and how fast do you wish to go?
     
  9. crowsridge
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    crowsridge Senior Member

    Hi Messabout. I have plans for the Glenn L Rogue Runner. It is only 6' wide at the widest outside. Then there are the frame members and gussets. Here is one completed in the picture below. Lots of lost space and all the new boats are wider here. My boys just ordered one 25' sled thats 9.5' wide. Very nice, but I dont want to drop the 50K
     

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  10. Ike
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    Ike Senior Member

    Are you planning on trailering this? If yes, then you don't want a boat 9.5 feet wide. frankly 6 foot beam on a 20 foot boat is more than adequate and stability has little relation to that as has been pointed out. What are you planning to do with this boat? That should be the major criteria that determines how big it is and what type of boat it is. You should not let yourself get bogged down in all these extraneous factors, length, beam type of chine etc. In boats form follows function. Boats are designed for a specific use and for ease of building depending on the material it's made of.

    Give us more info on how you plan to use this boat.
     
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  11. PAR
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    PAR Yacht Designer/Builder

    The 20' boat you're interested in is actually a stretch of a shorter design, so 6' seems a bit narrow, though is sufficient. You could have a 8' or 8' 6" beam on that 20' boat, but it will need more power (a lot more) to get the same preformance and your mileage will drop quickly, in comparison to the 6' beam version.
     
  12. crowsridge
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    crowsridge Senior Member

    If you look at how much space is lost in that picture, you'll understand. I use it here at home in a river that gets very shallow during the summer. I will take it to the Columbia river(can be big water at times) and take it over to the coast to do some crabbing and clamming. On a nice day even go over the bar with it. Crab rings take a lot of space. Then you have buckets to put them in, bait, guests and gear. Why be crowded? 9.5' is legal trailer width.

    Yes it is a GL sanctioned length change. And you are right about narrow. It would feel like a canoe if I'm not careful about my choice. ; )
     
  13. crowsridge
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    crowsridge Senior Member

    Oh. The 9.5' x 25' is just what the boys bought. They are branching out to guide service and need that much space. I'm good with the 8'x20'
     
  14. johneck
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    johneck Senior Member

    A difference between the bilge/chine is roll damping. There will be higher roll damping with a sharp bilge.
     
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  15. Hawkboat
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    Hawkboat Junior Member

    Exactly.
     
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