Mastless Crab Claw ?

Discussion in 'Boat Design' started by Canada Bob, Mar 10, 2011.

  1. garydierking
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    garydierking Senior Member

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  2. yipster
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    yipster designer

    Bob, got Marchaj out, a book you should read on this sail and when going to a lose foot on the crab claw that would take away almost half its power
    and reduce it to a low aspect latin -below a bermudan- in performance couse when no longer axi simetric most of its extra vortex lift is lost
    (like raising it to vertical) downwind al sails are sort of equal as only area is the drive

    Gary
    , thanks for the pic and info from a more experienced guy but can you say as i wonder if roping on the booms should affect vortex etc
    what i really mean is, do you know if any serious crab claw racing against bermuda sails has ever been done, proving Marchaj's observations?
     
  3. garydierking
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    garydierking Senior Member

    Harmen Hielkema did race seriously against other beach cats for many years and was as good or better depending to some extent on the skill of the opposition. Here's a video:
    http://www.youtube.com/user/vakaman#p/u/10/a4FADWXmuHk

    The vertically oriented crab claws like the Samoan one shown use draft in the usual way to generate lift. The raked back ones like Harmen's are cut flat and possibly use vortex lift. This is a highly charged subject in the proa sailing community and there is little hard data available. It is difficult to say whether the results are from the skill of the sailor or the sail rig itself.


    Gary
     
  4. Canada Bob
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    Canada Bob Junior Member

    Hello Gary,

    Thanks for the info on how folks sail in Samoa, news to me, thought it was just Rugby they were interested in. I'll have to take a close look at what they've been up to, and the Hawaiians too.

    Canada Bob.
     
  5. Canada Bob
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    Canada Bob Junior Member

    Thanks for that Yipster, two {or a dozen} heads are always better than one.

    I'm getting a better idea of what I need to do now, thanks to you guys...

    Canada Bob.
     
  6. Canada Bob
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    Canada Bob Junior Member

    I've had a 4 PM's asking what I was on about when I met with Casper Weinberger et-al, so rather than send the same email out 4 times, here's a link to the saga...

    https://www.uow.edu.au/~bmartin/dissent/documents/Norburn.html

    I hope it's not too off topic, afterall, it was a sink or swim things, so to speak...

    Canada Bob.
     
  7. Canada Bob
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    Canada Bob Junior Member

    THANKS for the nod in the direction of the Samoan {and the like} boats Gary, much appreciated, looks like my novel idea has been {more or less} done before.

    The Wayfarer on the link below is almost exactly what I have in mind, the more I look at the mast and the spar the more I'm seeing pole vaulters poles :)

    http://www.wharram.eu/photos/index.cgi?mode=image&album=/Ethnic-Designs/Tahiti-Wayfarer&image=Tahiti%20W%201232.JPG

    From what I see above chances are the best location for the sleeve and the pole might be between the hulls, anyone have any thoughts on that ???
    Other than that, why would they stay the mast half way up, rather than at the end of it with an {adjustable} inverted V ???

    I'm guessing that mast/pole is less than 12ft long too, that helps as vaulters poles go from 12ft to 15ft, and I can't think of anything more flexible to arc back from almost vertical to 60 degrees or less. Looks like that bloke above has his set to around 60 degrees, so my minds eye had that near enough. Then it's easy enough to stop any sideways waggle once the inverted V is attached, should be, could be real easy to set sail.

    I like this Y front arrangement too, real simple that is :idea:

    http://www.wharram.eu/photos/index.cgi?mode=image&album=/Ethnic-Designs/Tahiti-Wayfarer&image=Tahiti%20W%202970.JPG

    Looks like this might be a viable project after all, mind you might get better results if I head out to Samoa, or Fiji rather than Halifax Harbour :)

    Canada Bob.
     
  8. garydierking
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    garydierking Senior Member



    If you stay it half way up or more commonly 2/3 up, the sail will flatten as you sheet in harder, which is what you want going up wind. If you attach stays to the top only, the sail will have a fuller shape when sheeted in hard...bad.
    I've used a lot of old windsurf masts for these spars, and you can join two together at their bases to get up to a 30' spar.
     
  9. Canada Bob
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    Canada Bob Junior Member

    Right ! I'm learning fast {of what to avoid, at least, potentially a life saver} from you guys and I very much appreciate the feedback, can't beat the www when it comes to finding stuff out.

    As for the windsurfers masts, I wonder if they differ a lot from the vaulting poles ? add to that, how long a pole/mast would I need on a 16ft {home made} Cat ? as mentioned, I'm not looking to go anywhere fast, stability and tranquility are my catch words.

    Thanks again Gary for your input, valued and appreciated.

    Canada Bob.
     
  10. Canada Bob
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    Canada Bob Junior Member

    yipster;

    Bob, got Marchaj out, a book you should read on this sail and when going to a lose foot on the crab claw that would take away almost half its power
    and reduce it to a low aspect latin -below a bermudan- in performance couse when no longer axi simetric most of its extra vortex lift is lost (like raising it to vertical) downwind al sails are sort of equal as only area is the drive


    Marchaj hey, never heard of the guy, but read up about him since you flagged him for me, thanks for that. As to the loose foot, again, thanks for that, saves me flogging that dead horse ;)

    Canada Bob.
     
  11. yipster
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    yipster designer

    thanks for the link on u-tube where Harmen Hielkema races the crabclaw but not like a sailrocket
    he does sail the rig fast and looks good, elsewhere he mentions you too so i better dont be a wiseguy, still..

    is it not amazing that since 1964 when Marchaj wrote "sailing theory and practise" witch i read from the liberary
    and made me get "sail performance" a revised 2003 edition stating the same on his crab claw findings
    and its superior potential power over other rigs are still unconfirmed with little new hard data available..

    guess the delta sail must be outruled in racing and not well understood, than again i never build a small windtunnel
    like Marchaj also showed in "seaworthiness" to check windspeeds on the claw, nor have i tried those vortexes in cfd

    but someday, somewhere someone will and i'm really looking forward to that
     
  12. garydierking
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    garydierking Senior Member

    Bernard Slotboom submitted some newer research to the AYRS. I can send you the .pdf if you write me privately.
    gary dot dierking at gmail dot com
     
  13. yipster
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    yipster designer

  14. Pericles
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    Pericles Senior Member

    Try a Egyptian Felucca Lateen rig, using those vaulting poles.
     

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  15. Canada Bob
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    Canada Bob Junior Member

    Hello Pericles, I guess the poles might lend themselves to a Felucca rig, mind you they look like a fair weather / sheltered water rig to me, but what do I know. By the way, I'm not that far away from you at the moment, here in the NW of the Untidy Kingdom, in the bright lights, big city of Blackpool ;)

    Canada Bob.
     
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