Radiused mainsheet tracks.

Discussion in 'Multihulls' started by redreuben, Nov 21, 2013.

  1. redreuben
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    redreuben redreuben

    It would seem to be that the expense is not outweighed by the benefits on most boats except the top end racers, but then it would seem to me to be the ideal way to surround an expansive cockpit, at least on trimarans.

    What are the advantages re; Sail control ?

    And is the (vertical) gullwing an advantageous shape or just following the beam shapes ?
     
  2. michael pierzga
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    michael pierzga Senior Member

    Leech tension.

    You can generate leech tension with a vang, or the main sheet

    Modern sloops eliminate the traveller completly and sail on the vang.



    Dont know much about multi hulls

    In general travelers are a pain in the butt and completly dictate the cockpit layout
     
  3. philSweet
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    philSweet Senior Member

    The actual reason for wanting a curved track is to have a geometry where one control does one thing. So the main sheet only controls twist and the traveller moves the boom without disturbing the twist. That assumes adequate power for both functions.

    Another reason to do this is to create geometries where the required force matches available force. The traveller on my Catalina 38 is sharply curved upwards outboard so that the main trimmer can shift it with a 4:1 purchase by hand. If it followed the deck curve, like the factory version, it was nearly impossible to shift windward of center because you were also tightening the main. There are still a lot of boats with vangs that don't like taking full load going to windward. I set my vang to allow a certain amount of gust response that is controlled by the mainsheet. When single handing, my vang is a set-it-and-forget-it device. Racers use it differently.

    So two things - control independence, which is pretty important for coordinating a racing crew, or force and energy management to simplify handling. Shape is also used to manage the load path since the cars are derated for off axis loads and have more friction as well. It might be cheaper to have a carefully fabricated track operating near its limit as opposed to the next size up flat stock.
     
  4. Corley
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    Corley epoxy coated

    I'd tend to agree it's not really worth it except on race boats but it is a nice way to close the cockpit and mount staunchions which is a requirement under the Cat 1 safety regulations. I recall reading that it has some benefits structurally as a reinforcement to a x type trimaran beam as it helps to stabilize the beam structure fore and aft. As you no doubt realise the x type main beams are an attempt keep the heaviest parts of the beam structure centralized which is the root of the beam where it meets the main hull. This keeps the weight out of the ends of the main hull and the lighter traveler beam has the dual purpose of minimizing deflection and reinforcing the structure. As Michael notes it helps to maintain good leech tension as the sail is depowered.

    On a simpler boat you can get the same effect by closing the cockpit aft with the rear beam the earlier ORMA's for example addressed the issue by having a curved rear main beam that integrated the traveler as part of the beam structure. You can still have a curved track with a straight rear beam it's just not quite as elegant and gets in the way more as it intrudes into the tramp area the mainsail traveler on Pen Duick IV used this system. With a larger boat it's a safety issue as the traveler is in the working area and more likely to injure you in the case of an unintentional gybe.
     
  5. waikikin
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    waikikin Senior Member

    A similar effect can be indicated with the use of a mainsheet mounted to a track to boom also, traveller & lines set up neatly across the aft beam o a catamaran for example.
    Jeff.
     
  6. oldsailor7
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    oldsailor7 Senior Member

    The semi circular track is the very best option at the expense of cost and weight. (unless cleverlydesigned).
    On many home bullt Cats and Tris the mainsheet traveller is a straight, bulky, heavy and consequently ugly design. Some have the mainsheet tackle bolted to the floor in the centre of the cockpit, where it uses up valuable cockpit space and is even dangerous, given the high loadings that a mainsheeting arrangement can have.
    The clever combined mainsheet/traveller as used on the Buccaneer 24 design can be used on any of the smaller Cats and Tris, using only an array of blocks and jam cleats across the rear crossbeam.
    The KISS principle.
     
  7. Steve W
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    Steve W Senior Member

    The GBE cats used a radial track for the vang and Malcolm Tennant used to sell the track which was basically a curved I beam with lightening holes punched in it.

    Steve
     
  8. Baltic Bandit

    Baltic Bandit Previous Member

    Some Mini650s (Naciras) that use a radiused track. by eliminating the vang, you reduce the forward loading of the mast at the gooseneck and partners thus reducing failure modes. one of the issues of course is how you manage to move the car along a circular track.

    It also takes up a lot of space. Not as big a deal on a boat designed to be single or doublehanded, though it does make it a bit of a hassle to get back to the rudders if you need to make repairs.
     
  9. pogo
    Joined: Mar 2010
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    pogo ingenious dilletante

    Yepp, best solution for a straight travellertrack !
    Constant load on mainsheet, constant twist in mainsail.
    Track under Boom must be horizontal !

    http://www.sterrenkunde.nl/anw/navigatie2.jpg

    pogo
     
  10. bruceb
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    bruceb Senior Member

    boom track

    Thanks Jeff & Pogo, I hadn't seen that. How do you determine the angle of the track on the boom?
    B
     

  11. pogo
    Joined: Mar 2010
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    pogo ingenious dilletante

    When mainsail is set -and no wind in it- the track under see Boom should be approx. horizontal, see pic of Simac.
    http://www.sterrenkunde.nl/anw/navigatie2.jpg
    Note the "catching rope" for the car on boomtrack. In a powergybe it stopps the car few centimeters in front of the stopper at track's end---a stopper can't sustain the enormous kinetic energy ( i've destroyed mine )

    Playstation
    http://www.calvertsails.com/images/playstaion pix/repairing mainsheet.JPG
    Note massive stopper with probably four 10mm screws. But what the hell the white rod is for ? Anyone an idea ?

    By the way, this travellersystem cries , at least on bigger boats, for an endless mainsheet system of such type:

    http://www.apsltd.com/images/CATEGORY/medium/654.jpg
    (one can give "more" tackle , f. e. a third block between B and B and a double block A ; or more...)



    pogo
     
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