CE and CLR moved forward, balance problems?

Discussion in 'Boat Design' started by dustman, Aug 17, 2022.

  1. dustman
    Joined: Jun 2019
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    dustman Senior Member

    Would moving the center of effort and center of lateral resistance well forward of mid ship cause any handling/balance problems?
     
  2. Milehog
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    Milehog Clever Quip

    Probably.
     
  3. bajansailor
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    bajansailor Marine Surveyor

    Can you elaborate a bit more please about these moves?
    Is this a new design that you are working on?
    What type of sailing boat is she, and how large?
     
  4. dustman
    Joined: Jun 2019
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    dustman Senior Member

    I would like to move the masts forward on a 12' x 24' biplane rigged catamaran with freestanding masts. The mast bases would be part of the same structure as the front crossbeam attachment to the hulls. This will result in the CE being fairly far forward. The thought is to move the CLR(daggerboards) forward to compensate, but not sure what unintended consequences this might have, but it would greatly simplify the design and save a lot of material and other complication, and make the deck cabin layout and balancing weight fore/aft much easier, and allow a more practical layout.

    This is a potential change to the original design. I am slowly working on designing 3 different boats. First will be the small solar electric catamaran which should be in the water in less than 2 years. Second will be a small sailing catamaran. If all that works out then a 40-48' sailing catamaran for ocean passages. Before any of that going to build a really small catamaran for testing resistance and design ideas.

    It's amazing how much more complicated things become when you add sails to a boat.
     
  5. rnlock
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    rnlock Senior Member

    If you moved everything far enough, it might make tacking more difficult. Many catamarans are hard to tack already. OTOH, if you could steer that forward board, as well as the rudder, maybe it would be no problem.

    Phil Bolger experimented with moving centerboards forward to get them out of the way. In Boats with an Open Mind, he has a couple of boats where he's done this. In his case, he doesn't move the rig, but uses a larger rudder to compensate. If I remember correctly, he says his Dart Dinghy tacks ok, but the handling can be odd during a tack. It's kind of a skimming dish, so it might be much less likely to have problems with tacking than a catamaran. His Cartopper is a bit less extreme, and he says it handles fine. But it's not long and skinny like a catamaran. In the same book, he also has an experimental design called Canard, with the rear board fixed and further back, and the front board steerable. Apparently, it's hard to tack and he writes that if he does another boat like this, he'll make both boards steerable.

    The Yorkshire Coble has most of its lateral plane right up front, but again, it's a rounded hull.
    https://i0.wp.com/lodestarbooks.com/wp-content/uploads/2019/01/Cobles-3.png?ssl=1
     
  6. Will Gilmore
    Joined: Aug 2017
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    Will Gilmore Senior Member

    A thought to consider. By moving the CLR forward, assuming you are leaving the rudder the same, you extend the distance between the CLR and the rudder. If you do this, understand that the CLR is also, typically, the pivot around which steering works. Of course, you boat isn't likely to actually pivot on its CLR, but instead, scribe a curve as it turns. However, the responsiveness of small boats vs large boats has a lot to do with how close or far apart these two points are.

    I don't know anything about tacking a biplane rig. I would assume you could potentially luff or even backwind the windward sail and use the leeward sail to sail her in a semi-circle around the windward sail, to weather until you were into the wind. Then you would want to luff the leeward sail and backing the windward sail until they crossed the wind and switched their orientation to the wind. I would think, if my vision is accurate, that keeping the CLR forward with the CE would be better then leaving the CLR aft. You would get less tail feathers on an arrow effect and better turning around a point that has a smaller lever arm of resistance.
     
  7. Milehog
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    Milehog Clever Quip

    I think this would unbalance the boat weight distribution wise.
     
  8. Skyak
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    Skyak Senior Member

    In addition to the challenges noted, you need to think about how the boat behaves when heeled or pitching. Old boats had their max beam ahead of their center of buoyancy so that their keels increased angle of attack and their bows lifted when they heeled. Modern boats prefer longer sharper bows -max beam aft of center.
    High performance sailboats have been moving the mast and centers aft to keep the taller rigs from pushing the bows down.

    Moving the foil centers away from the maximum beam is giving away righting moment.

    There is a class that does as you say -it's a rule that intentionally limits how far the rig can be from the bow to limit the performance of the class. Dolfman has posted many studies noting these effects and free software if you want to prove it to yourself.
     

  9. sharpii2
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    sharpii2 Senior Member

    One problem to consider is that the hull itself has a CLR.

    Ideally, that would be close to the 'board or keel CLR.

    If you move that further foreword, you have a spread between the 'board or keel CLR and that of the hull.

    This could make it hard to turn, especially if the hull is deep in relation to its WL beam.

    Working garvies had their rigs and center boards way up forward. This was to clear most of the hull for its cargo of oysters or clams.

    Garvies (which were relatively narrow scows), like their sharpie counterparts, were oar assisted sailing vessels. They had very shallow hulls, so they could more easily get away with this.

    I encourage you to make a scaled model of your boat, with these changes, to see if there are any problems.
     
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