Best Rig Type For Downwind On Power Multihull

Discussion in 'Motorsailers' started by GalenP, Jul 27, 2016.

  1. GalenP
    Joined: Dec 2012
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    GalenP Junior Member

    Hi All.

    Imagine a power cat, with displacement type hulls, capable of around 18 knots under power. A fairly small boat, say 30 feet, with minimal camping accommodations.

    What type of sail rig would be best for downwind assist, to a broad reach?

    The rig needs to be dead simple, and needs to be easily lowered and out of the way much of the time. There will be no rudder, just outboard motor steering.

    Some form of headsail only rig? Balanced Lug? Mainsail only? I really have no idea.

    Thanks all.
     
  2. luff tension
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    luff tension Junior Member

    Kite. Find a local kiteboarder with the biggest kite around and get them to hop on and give it a go.
     
  3. GalenP
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    GalenP Junior Member

    Thanks. So, a kite? Where I will use the boat (Pacific North West), the wind is not very consistent. Lite to gusty in moments. At this point I am not sure that is the solution for me.
     
  4. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    If looking for a dead simple rig, forget about the kite, which simply isn't very practical for your needs.

    A simple Bermudian cat, employing a production mainsail will be the simplest way to go, parts will be readily available as will setup, hoisting and dousing operations too. Of course, you'll likely need to hire someone to balance this rig over your boat's specific configuration, but this isn't very costly, nor difficult. Which boat are you looking to do this too?
     
  5. FAST FRED
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    FAST FRED Senior Member

    For downwind a square sail is very effective , but a bear to live with.

    The simplest EZ to operate setup is a roller sail with double luffs.

    In other words 2 identical sails sewn to the roller wire.

    Sewing to a chain is far better as the sail can be folded and put in a bag.the luff wire has to be coiled or left standing.

    Two poles are used to steady the sail when it unrolled and the sheets to the clew lead thru the poles.

    This can be used downwind and with the poles set to allow the sail to V forward it works as a very steadying sail , almost self steering.

    With one pole eased fwd it will do OK at modest broad reaching too.

    This sail setup was invented by Wright Brittan (SP?) in the 60's and used for transatlantic and northern waters adventures.

    For a boat that will be under massive power (18K in a 30 ft boat) only a fully battened main sail will function as the wind will almost always be from ahead , as with an ice boat..



    The
     
  6. GalenP
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    GalenP Junior Member

    Thanks. The boat does not exist yet. Its a concept power outrigger idea I may build in the future.
     
  7. brian eiland
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    brian eiland Senior Member

  8. brian eiland
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    brian eiland Senior Member

  9. PAR
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    PAR Yacht Designer/Builder

    There's nothing simple and cheap about an aft mast rig. Just think about the reinforcements for the standing rig, that'll need to be put in the hull for such a rig.

    A freestanding, low aspect Bermudian cat is about as simple as it gets, boomed (my preference) or boomless. All you need is a stout step, no chain plates, no stays or shrouds, a single halyard and that's about it.
     
  10. brian eiland
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    brian eiland Senior Member

    Solitary Island Catamaran example

    You're going to say a free standing mast in a multihull is easier to secure than my aft mast?? :confused:

    Let me submit one example of an adaptation of my aft mast concept to a production kit boat I was fond of, but they decide not to continue with their project for financial reasons.
    Solitary Island 40
    (no longer available on a website, but I included the original PFD attached)

    If you go to this page of my website you will find a few drawings that depict a large trapezoidal shape object beneath the mast tube that is stepped at cabintop level in a manner that does not NOT impart bending loads to the mast step, nor the bulkhead. The 'mast step' spreads it loads out onto the cabin floor which in turn is reinforced by the wave-splitting structure running fore-to-aft. It is also attached to the rear bulkhead that is both substantial in itself and its anchorage in the vessel. The cabin door is off-center.
    Profile 60, aft mast.jpg
    Mast Rig, full size jpeg, med size.jpg

    Take note that the vertical backstay (the mizzen is mounted on) is very tight to help maintain forestay tensions. Interestingly it pulls up on the mast step structure while the mast pushes down.


    There was a really nice kit-based catamaran that was being worked up over there in Aus, the Solitary island 12M. I was looking to make available a mast-aft option for it. Here is one posting I made that showed a few mods I had in mind initially:

    I was suggesting an 'X' structure built into the aft bulkhead of the cabin to support the mast compression loads.
    TopView, mast X support location.jpg
    Side Section View, trapazoidal shape of mast support.jpg
    Solitary transom.jpg

    So we need a nice trapezoidal shape 'bulkhead' under the mast, that it would be nice to extend portions of it to the full beam of the boat that then anchors the widely spaced shrouds to. (this should be done in almost any other vessel, mono or cat, rather than depending on open shell surfaces surrounding interior spaces to support a rig). Then preferable we add a longitudinal rib down the centerline of the catamaran to give it some rigidity in lue of the keel on a monohull (another item that should be included on any catamaran).
     

    Attached Files:

  11. brian eiland
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    brian eiland Senior Member

    All Three Sails Roll Up, or each Individually

    I think the description on my website meets your needs, albeit a bit larger version than you want.
    http://www.runningtideyachts.com/gamefishing/

     
  12. PAR
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    PAR Yacht Designer/Builder

    There's nothing simple about an aft mast rig.
     
  13. brian eiland
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    brian eiland Senior Member

    Could you detail that? Its really not as difficult as you and some others make it out to be. No one has yet offered a decent challenge to by rig force analysis?

    I've had lots of naysayers over the years on this subject thread, and I think I have answered most of them. I'll be writing something new here soon for another skeptic, and I'll like post it over there as well.

    BTW, I recently posted 3 new postings (#998, #999,#1000) in support of the "main-sail-less" aspect deemed appropriate by sailors themselves.
    http://www.boatdesign.net/forums/sailboats/aftmast-rigs-623-67.html

    Again I would issue this challenge:

     
  14. brian eiland
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    brian eiland Senior Member


  15. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    So, simple mast raising and dousing is comparable to say a freestanding Bermudian cat? I read the requirements as easy to raise and lower and out of the way, most of the time. What about the huge amount of structural reinforcement that will be necessary on the power cat, just to accept the aft mast setup? Yeah, not a simple thing IMO . . .
     
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