Crabclaw rigs

Discussion in 'Multihulls' started by guzzis3, Jun 19, 2019.

  1. guzzis3
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    guzzis3 Senior Member

    Me again. Still haven't done anything about the tiki21, but this has been rattling around in my head since the post about the manu kai so...

    First I don't believe the claims made of startling performance of crab claw sails but I guess they must be acceptable for a cruising cat. With that in mind has anyone ever built an A frame mast forward to carry the upper spar of a crabs claw ? I'm thinking a pivoting A frame able to rock forward and back a bit and the upper spar anchored to the bow beam and able to slide port and starboard on a traveler track. The aft end of the lower spar controlled by a double mainsheet or mainsheet traveler. The A frame has to rock to accommodate the arc the nose of the rig would swing through.

    Why do this ?

    Well no chainplates or shrouds. One sail, 4 spars, 1 or 2 tracks and 1 or 2 blocks and some polyester lashings and a few bits of hardware.

    If the boat is trailerable you could fast the upper spar to the apex of the A frame laying flat, attach a block from the nose of the upper spar to the track on the bow beam, pull and jiggle and it'd rise up like an umbrella. No temporary triangulation or gin pole.

    It'd want to be fairly high aspect, I think you could get about 2 1/2:1

    Obviously douse the sail by raising the lower spar.

    What have I missed ? It just seems to lend itself to the structure of a cat really well...

    On a cat about say 24' long beam 14', the A frame could use 14' spars, the sail spars about 8 or 9 meters and the gap from the beam the A frame sits on to the bow beam about 5' or 6'.
     
  2. Clarkey
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    Clarkey Senior Member

  3. rwatson
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    rwatson Senior Member

    I can never figure why anyone would install a windward handicapped rig on an already windward handicapped hull shape.

    Its almost like they expect just ideal winds.
     
  4. Corley
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    Corley epoxy coated

    On the modern vakas they switch to Bermuda type rigs offshore then back to crabclaw when near the coast.
     
  5. misanthropicexplore
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    misanthropicexplore Junior Member

    If I understand what you are saying, I've seen it on a sketch of a proa, thought I don't know if the sketch was ever turned into an actual boat.
     
  6. guzzis3
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    guzzis3 Senior Member

    Thank you for the replies.

    I had seen the tiki 21 page. That boat uses a conventional mast from what I can see. Part of my interest is that the A frame suits a catamaran's construction while a single centrally stepped mast really doesn't.

    misanthropicexplore What you may be referring to is a mast plus a side prop. Gary Dierking talks about doing that to depower in gusts. What I am proposing is a tacking rig with the triangular sail and spars hung from the apex of an A frame and the "nose" attached to the front beam. They together form a sort of tripod so no further supports are needed, then the mainsheet controls angle at the back. However that arrangement means the upper spar can't swing with the sail, so I thought put the nose on a track so the 2 spars and sail can swing together, but the beam/track is straight and the nose needs to transcribe an arc, so you allow the A frame to pivot forward and back a little to accommodate that. It sounds dodgy and as though it wold all collapse but if you get the proportions right it can't.

    People have done the A frame thing, and aft stepped masts, but often these experimental rigs are low aspect ratio, some suffer inadequate area.

    I'm not looking to put it on a wharram. I've been thinking of that manu kai, such a pretty boat. Something with rounded hulls and lee boards.

    Anyway...
     
  7. guzzis3
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    guzzis3 Senior Member

  8. rwatson
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    rwatson Senior Member

    Just by accident, I came across this video, experimenting with a Crab Claw Rig.
    Might be worth a look
     
  9. guzzis3
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    guzzis3 Senior Member

    I am just gobsmacked, which doesn't happen often to cynical old me.

    I've seen those T masted things on other boats but that one must have been installed by Heath Robinson. And why oh why would you put it on a mac 19 FGS ???

    The whole idea behind my thingy above it that while it probably gives up some windward ability it massively simplifies the rig and lends itself to the structure of an open deck cat. 2 short spars, 2 long, some lashings, 2 brailing lines 2 mainsheets. No winches, halyards, battens, shrouds etc etc...dirt cheap and simple to build and dead simple to sail. Also simple to step. If you can get teh upper spar sifficiently vertical you don't even have to swing the nose across the front beam.

    Anyway thank you for the link to the video. It was horrifying...
     
  10. Alexx
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    Alexx New Member

    download (7).jpeg download (2).jpeg download (7).jpeg download (2).jpeg
     
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  11. guzzis3
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    guzzis3 Senior Member

    Thank you. I had not seen that. Any comments on how it sails ?
     
  12. Alexx
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    Alexx New Member

    No idea but it was on sailing anarchy and in wooden boat..... images (1).jpeg
     
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  13. rwatson
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    rwatson Senior Member

    You're welcome.
    I understand your reaction - it's the same one I get whenever I see ANY Crabclaw arrangement. It's like seeing a Dutch Windmill vane on a modern wind generator. :)
     
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  14. guzzis3
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    guzzis3 Senior Member

    Have a look at Mr Denney's post on the tiki21 thread. That model seems to sail quite well. It's a proa of course but more similar to what I'm thinking than the heath robinson arrangement above.

    I still can't believe anyone would do that to a mac 19. Obviously they aren't great sail boats, so that's a reason not to, but they are also fairly rare by macgregor standards, only made for about 3 years before the 26X superseded them. They are somewhat sought after in mac circles...just bizarre...
     

  15. guzzis3
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    guzzis3 Senior Member



    This person has built basically exactly what I am thinking on a hobie beach cat. Very interesting. He's not trimming properly in this video but it's worth a look...
     
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