Best rig for small catamaran circumnavigator?

Discussion in 'Multihulls' started by randy quimpo, Jan 23, 2006.

  1. jamez
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    jamez Senior Member

    Rob,

    "Your reasoning implies that monos are better cruisers than multis as they are more "ubiquitous".

    Actually it doesn't (although many mono's of course have sloop rigs). Mono's are ubiquitous because for most people they also work well. That is not to say that in some respects a multi can't do some things better but that is something people often have to experience before they will countenance a change (like me;-).

    "I believe that stayed sloop rigs are ubiquitous because a) they are what racing boats use"

    And racing boats use them use them because in spite of the inherent drawbacks described above, in general, if they are properly engineered, they work well (and in the vast majority of cases stay up).

    "and b) because sailors are very conservative".

    Absolutely agree. Further, I would suggest that sailing conservatism is kind of self perpetuating as it is fuelled by the knowlege and acceptance of what is familiar and what people feel comfortable (in some cases to trust their lives) with.

    While I would describe myself as a conservative (now cat) sailor in a lot of ways, I've got an alloy mast on my Wharram so I'm not a complete Luddite ;-). It has been interesting following the development of the various Harryproa and I look forward to seeing Solitarry launched and campaigned.
     
  2. rob denney
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    rob denney Senior Member

    G'day,

    I have experienced both types of rig, whereas you have yet to sail, maintain or buy an unstayed one. I look forward to taking you for a sail later this year. I also like to watch and sail on all types of boats, but when it comes to buying or maintaining them, the unstayed rig wins hands down. For a round the world cruiser (original subject) or a fast boat (morphed subject) the unstayed rig has far more going for it than the stayed rig.

    I would also like to apologise for the unnecessarily caustic tone I adopted for my reply to you and Ross. Been a bit full on getting the design for the 50- footer finalised and the workshop sorted, so I was a little less careful with my editing than normal.

    Regards,
    Rob
     
  3. sigurd
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    sigurd Pompuous Pangolin

    masts suck

    (edited to remove offensive slant :p )
     
  4. leemolou
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    leemolou New Member

    What about 2 hulls you can sail in both directions (like a proa) but with the masts not exactly at the same distance of the bow... that way, you could always have the windward sail behind...

    M = Mast

    ----M-------
    --|-------|
    -------M----

    just a thought!
     
  5. MAINSTAY
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    MAINSTAY Junior Member

    Try this.

    I suggest the best rig for a small catamaran for curcumnavigation is one that is simple to build, easy to operate, and reparable at any landfall. One without exotic materials, without moving parts, yet still get the most from your sails.

    Specifically I suggest a modified three-stay rig. With it you can use a fuller roach for more sail area or a shorter mast with the same area. The fuller roach also improves the efficiency of the sail area you have. There are 3 modifications as shown in the attached xls drawings:
    1) Relocate the maststep forward 1/3 the distance toward the forestay and then 1/6 the beam either port or starboard, choose one, (the masthead is to remain in it original position and the mast raked and canted),
    2) Relocate the shroud on that same side to be abeam the mast,
    3) Relocate the other shroud to the original maststep.

    The mainsail is flown from #3 (now a mainsailstay) and no sail is on the mast. The mast is mainly in compression without major bending or torsional stress. The step is closer to the end of the cross beam rather than at its midpoint.

    There is more drive from the mainsail because there is no wind shadow at the luff. Other boats with aft masts and bipod rigs have reported that there is a 15% increase in speed when the mast is not shadowing the luff. That added speed can mean quicker passages and less exposure to stormy weather at sea.

    I also suggest exterior blocks and halyards for ease of inspection, maintenance, and repair of the running rigging in any port.

    Fair weather and happy sailing,
    LarryModes@aol.com
     

    Attached Files:

  6. Speng
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    Speng Junior Member

    While I might not agree that an unstayed biplne rig is the "best" rig (mainly because it is difficult to say what "best" means for everyone) I will say that an unstayed carbon (or other composite tube) should be very reliable. The design is fairly trivial, the material is highly resistant to fatigue, the lack of fittings eliminates, almost completely, stress concentrations. Also the repairability of aluminum is not as simple as you think for a circumnavigator as you may find yourself hard pressed to find a rigger or Aluminum welder in many parts of the world not to mention the specialised fittings you might need because yacht chandleries aren't everywhere.

    The Radical bay rig concept isn't the only one out there for a simple unstayed rig. I'm personally a big fan of windsurfer style rigs (they usually look weird because somebody's stuck a fiberglass winsurfer rig on a ordinary looking hull - e.g. a Wyliecat) but they work pretty well for many cruisers and racers and the design of the mast is further simplyfied because the boom is connected to the mast differently (or not at all). Also to be taken into account is the simplicity of the running rigging: two (lightly loaded) mainsheets, cunningham, outhaul and that's it.

    I think a problem many have is the lack of foresails esp for light air and downwind work but there's no reason why they can't be added.
     
  7. sharpii2
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    sharpii2 Senior Member

    I see three problems with this proposed sail plan.

    1.) The mast will be too far forward. Multihulls have been known to dislike this mast placement. It tends to make them steer wildly and even pitch pole.

    2.) The rig would put enormous compression forces on the cross beam not to mention enormous tension loads on the outer hulls and/or crossbeams, forcing the designer to design them much stronger and probably much heavier.

    3.) the sail would be difficult to reef and, once reefed, the Center of Area (CA) of the sail plan will be too far forward, which would, not only make the boat hard to sail any direction but down wind, but would also help encourage it to pitch pole.

    With a fractional sloop rig, the jib can come down by the first or second reef, removing the considerable compression forces needed to make it stand well in strong winds. This relieves an impressive amount of strain on the rig when it faces its greatest structural challenge. Not only that, but as the mostly triangular mainsail is reefed, its CA moves forward close to where the CA of the combined jib and main used to be, allowing the boat to keep its former balance.

    Such a rig can be remarkably cheap and easy to set up if one is not too enamored on high windward performance. The one I had on my weekender had a considerable amount of slop, but had no trouble getting me to windward (though not fast enough to win any races).

    And for that reason, it can be more easily maintained and repaired. Maybe that's why it is so ubiquitous.

    Bob
     
  8. OldYachtie
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    OldYachtie Junior Member

    Catamaran with wing sail in bi-plane format online

    To see a catamaran with a wingsail biplane rig designed for home building, see www.dunnanddunnrealtors.com/Catamaran.html . Why build a wing mast when you can build a fairing using foil-shaped battens? You don't get the "clingyness" of a cloth fairing if the batten fairings hold the cloth away from the mast. There are many wing sail and biplane rig links there, as well.

    Also featured on the site is my idea for making radius chine designs easily built in fiberglass.
     
  9. Richard Atkin
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    Richard Atkin atn_atkin@hotmail.com

    I am considering putting a crab claw rig on my future catamaran. The bottom line is this...the sail is more powerful than any other type of sail, except when pointing high to windward. It has a low centre of effort, and puts very little loading on the rigging and hulls compared to a fractional rig.

    However, it seems to be a very misterious thing, because nobody seems to know much about it. Maybe the sail area becomes too far forward for a cat, when sailing downwind??? Does this cause handling problems?

    Anyone have any reasons why a cat claw should not be considered?
     
  10. rob denney
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    rob denney Senior Member

    G'day,
    The arabs (dhows with lateen rigs) and the Pacific Islanders (proas with crab claws) seem to know a fair bit about them.
    The thought of those two booms/yards thrashing about in a gale is enough to put me off them for offshore work. Still, they are pretty cheap to try so give it a go and let us know how they work. Check into the proafile group at Yahoo and ask your question there. A lot of them have small and medium sized crab claw experience.

    regards,

    Rob
     
  11. Richard Atkin
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    Richard Atkin atn_atkin@hotmail.com

    excellent...I'll do that

    cheers Rob
     
  12. JCD
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    JCD Follow the Bubbles!

    Rob,

    I have huge respect for your hands on and practical thinking, but why would any skipper allow anything at all to be thrashing about in a gale? Inshore, offshore or even on the hard?

    I may have been there in a former life, sadly I don't remember, but I think the Poly's crossed oceans with crabs and even they may have had enough sense to reduce forces on the sails or at the very least rig up some preventers. Would you agree?

    My memory fails me at the moment and I am really racking my brain to think of it, but does anyone remember the crossing of one of the Cape's with a claw? I might be wrong or could have read it wrong.

    J:cool:
     
  13. OldYachtie
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    OldYachtie Junior Member

    Crab claw sails

    I have read claims that the crab claw sail actually develops lift and so depresses the lee hull less than any other rig. It was, of course, invented to use on catamarans, so it must surely be suitable. It doesn't look very versatile for reefing. One brails the yard and boom closer together instead of reefing, but I would think that you would have to quit sailing sooner as the wind picks up than you would with any other sail type.

    Sizable crab claw rigged boats would traditionally have had large crews, so I am not sure that it will be easily handled on a boat of any size beyond a daysailor. I think you have to dip it to come about, which sounds rather scary. I wouldn't put it inside a bipod mast, because that would limit the sails ability to lift its boom. If you google "proa" you might find more info.

    This rig is still in use in Tuvalu, Kiribati, the Marshall Islands, and in the Caroline Islands. I saw it in use in Tuvalu (the island of Nukufetau) and in Kiribati in the late 1970s.

     
  14. MAINSTAY
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    MAINSTAY Junior Member

    Bob,
    Sharpii2 wrote

    Response 1) Only the maststep is moved forward. The sails remain unmoved. The main is NOT set on the mast but on a vertical stay at the mainluff. The CE does not move forward and cause the problems you list. And since ther is no backstay, the mast could (with corresponding movement of CLR) be moved aft until the vertical mainluff stay rises from the transom, and there is a mezzin-like mainsail.

    Response 2) The rig does puts lower compressive forces on the cross arms, and may put minimal compressive forces on it since the step may be at or neat the side of the hull. See the attached file. The lateral base of the rig is simmilar to that of a monohull, so the design would have to be of similar strength and weight.

    Response 3) Reefing the main is the same as for the jib. No more difficult, and perhaps safer because the crew is not on the foredeck. The main can be roller furlled like a jib because the main is on a stay, like the jib. The movement of CA during reefing is no different than on the sloop rig.

    What else?

    Larry Modes
     

    Attached Files:


  15. sharpii2
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    sharpii2 Senior Member

    Hi, Larry.

    I still maintain my main points. And here's why.

    If the mast is on one end of the crossbeam, the 'luff stayed' main is going to act much like a conventional jib. It is going to need enormous tension to hold the luff reasonably straight. This, in addition to the enormous mechanical disadvantage the mast is going to have, being that it is tilted toward the luff stay, is going to put much more tension on the stay on the other side of the mast than even the luff stay is experiencing.

    This, in turn is going to increase the compression on the mast step by a larger degree than even a mast aft rig.

    I do see, however, how the bending moment on the cross beam will be less than I thought. I was and still am unable to see your actual drawing. But the tensions on the rigging in general, and the opposite stay in particular, may make the idea unworkable. Bending moment on the mast in compression has to be watched as well, as the mast is tilted and under a great deal of compression. Moving the mast closer to the luff stay and further away from the opposite stay may help a great deal, yet still maintain spirit of the design.

    Since the Main sail is presumably triangular, the center of area moves forward no matter how you reef it. This can be corrected by either having tandem boards, where the aft most one can be retracted as the sail is shortened, or by having a modest mizzen sail which stays set as the main is reefed. Either way, proper balance could be maintained. And on an ocean sailing boat, balance equals good course keeping qualities.
     
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