Ideas for unusual air draft requirement

Discussion in 'Boat Design' started by Markusik, Jun 29, 2018.

  1. Markusik
    Joined: Jun 2017
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    Location: Lake Michigan

    Markusik Junior Member

    A hypothetical sailing (coastal cruising) catamaran, S/V Hypothetical (LOA 12.9m BOA 7m), has a list of requirements. The most challenging requirement is that the captain must be able to modify the air draft from 15.5m to 4m, and back again, shorthanded on calm waters.

    Fulfilling this requirement will allow the owner to pass a low fixed bridge. The cat can then be stored on private property, avoiding a lifetime of marina/mooring costs and mast stepping/unstepping fees. It would also make for an extraordinary river explorer.

    I have a thought how this might be accomplished, but rather than distract with my idea (yet) I’d like to hear yours. All practical ideas welcome.

    Thanks in advance.
     
  2. Rurudyne
    Joined: Mar 2014
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    Location: North Texas

    Rurudyne Senior Member

    Single Handed Mast Stepping without a Crane - SailNet Community http://www.sailnet.com/forums/seamanship-navigation/280689-single-handed-mast-stepping-without-crane.html

    This thread was about basically what you were interested in. Look at post 5.

    A pulpit mast with an aft support as shown, just looking less cobbled together and more official design feature, might do the trick. You might also consider an A-Frame mast.

    For a cat I'm wondering if a biplane rig variant may help since roller furling may not be doable? Have to check with someone more knowledgeable if that rig is easier to handle short handed.

    If someone could give a way to overcome the issue with roller furling the Aft Mask rig might be worth looking into. Maybe with an A-frame mast as well.
     
  3. DCockey
    Joined: Oct 2009
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    DCockey Senior Member

    Why would roller furling not be feasible?
     
  4. Rurudyne
    Joined: Mar 2014
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    Location: North Texas

    Rurudyne Senior Member

    My thinking is this: roller furling, at least roller furling that isn't contained within a mast but is around the a line, seems like it's adding complexity.

    I may be wrong but folding up one with a regular or Aft Mast rig folded forward seems like it could be finicky. Maybe even at risk to fall in the water if you get careless.

    With a mast that folds back do you 1) have some mechanism to keep that line taunt when raised if it's the line also used to raise the mast or 2) disconnect the line the furling sail is on, possibly hooking it up to something else so it doesn't become unsecured?

    As for roller furling within the mast, wouldn't that make the mast heavier and harder to raise or lower?

    Maybe a classic unstayed junk rig or cambered junk rig in either regular or biplane may be easier to live with that trying to get automated?
     

  5. Markusik
    Joined: Jun 2017
    Posts: 9
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    Location: Lake Michigan

    Markusik Junior Member

    Thanks Rurudyne, those are good ideas. The difference in scale between a 7m trailerable and this hypothetical 12.9m cat is considerable, but nothing good engineering and money can't overcome I'm sure.

    My solution was actually a freestanding junk-like rig in a back-folding hinged tabernacle. Carbon fiber mast, carbon fiber wishbone battens, varying (flatter up high, fuller down low) degrees of camber sewn into the 5 or 6 individual panels, basically a 12.5m by 5m rectangle. No standing rigging, no chainplates, no foresail, just two sheets and a halyard.

    That would be a very big sail, but would lend itself to electric winches (3 total) and a degree of automation. The mast would be placed quite fore, although not as far as a catboat, allowing for a big saloon (galley up is a requirement) while still keeping a good sized trampoline.

    I should mention that other requirements for Hypothetical include interior saloon helm/nav station with cable steering, but sail management, (outboard) engines and autopilot interface all accessable by Bluetooth/wifi and an iPad app. The nominal helm station would be at the fore of the saloon, the actual helm station could be wherever the iPad is. Said app must also be able to autonomously reef, or loosen the sheets, to prevent mast damage or capsize.

    The junk rig's ability to reef immediately at any point of sail played a big role in my thinking.
     
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