New Type of Sailing Rig

Discussion in 'Sailboats' started by alan white, Mar 17, 2007.

  1. alan white
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    alan white Senior Member

    I have modelled this rig, but not experimented with it.

    The basic plan goes like this:

    A mainmast penetrates (or is tabernacled) very close to the bow. This spar is about the height of a gaff mainmast. The mast is raked back so that a plumb backstay becomes positioned to replace the normal (lower) luff of a typical gaff main (sloop). About 12 degrees now seperate mast and backstay. The backstay, then, is where the mast usually is located.
    Another 12 degrees or so forward of the raked mast, a fore stay runs from masthead to bowsprit. The bowsprit is mounted against the foot of the mast.
    A boom is mounted on a rigid stanchion (stanchion serves to prevent laterally loading the backstay). The stanchion rises to the height of the boom attachment point.
    A foil-section spar (gaff) is affixed to slide up or down the "backstay", the gaff's foot being located half distance between boom and masthead. It is also slidingly affixed just under the masthead, and it curves aft and extends above the masthead to a distance equal to half the lower luff. The upper sliding attachment is also made to allow the gaff to lower, leaving the sliding pipe still attached to the backstay.
    In this way, the gaff, being narrow athwartship, but wide fore and aft, and curved also, allows an elliptical sail shape when battened. In addition, no further backstay is required, so the boom may extend well over the stern.
    Reefing height (perhaps allowing two good reefs) is the distance the foot of the gaff can be lowered from its uppermost position, so the gaff foot will lower from halfway between the boom and the masthead down onto to the boom itself. The mainsail below the gaff's foot is hanked onto the backstay, and laced above onto the gaff (while also fitted into a slot in the aft edge of the gaff). Hence, there will be no hanks attached at lowest reef position.
    Fore/aft distortion of the backstay (halfway up luff-backstay) is prevented by a single aft spreader mounted between the mast and just above the gaff's foot (sail all up). This allows the gaff foot fitting to ride vertically in such a way that the mid-attachment point of the gaff rides from masthead down to just above the spreader exactly as the lower attachment rides down and contacts the boom when deep reefing.
    A pair of backswept shrouds are affixed to the mast at the root of the spreader, and they are attached to chainplates to each side of the backstay stanchion.
    Another pair of shrouds go from masthead to the same chainplates.
    So far, it seems without further staying, the backstay is still able to be distorted side to side. Also the mast may be bent forward at the spreader.
    Regarding the fore and aft mast bend: A single stay is attached below and aft of the spreader root, and this terminates on the forward face of the stanchion/deck juncture.
    Regarding the side to side stiffening of the backstay (due to the upper gaff being pressed the other way in strong breezes), a set of shrouds are attached to the tip of the spreader (where the spreader is attached to the backstay). These stays run to the chainplates. The chainplate position allows all shroud/deck attachments to be adjacent to the (shall we call it a luff-backstay?).
    This positioning allows the boom to be eased forward to ninety degrees before contacting the shrouds.
    A single chainplate per side handles all terminations except the forestay, which as said terminates on the bowsprit, having a typical bobstay and whisker stays.
    A jib completes the rig. Because the mast is completely bare of fittings on its forward-facing surface, the jib could cover the entire fortriangle if desired, lapping the mast in any case (and slipping nicely around it).
    Advantages: Low windage short mast; no running backstays; elliptical sailplan; fantastic leading edge characteristics (hanks and foil gaff); longer boom if desired; wire passing through cabin in tension rather than mast or post in compression; round or square mast is stiffer for weight; Mast can bury/compress into bow, the strongest point possible; Rig is easily lowered and inspected/repaired at sea---- the mast is very far forward, like a catboat's mast. It is canted back however, so it is stayed where the boat is wider, and hence can be deck-mounted and light. It seems that if the mast were as long as the boat, the masthead would, on lowering, fall within reach from the cockpit.
    The gaff spar might be of carbon fiber and be very light. A carbon mast could be round and also light, while not so long or complicated as would make it too expensive. I would opt for a hollow tapered square-section spruce or fir mast, which is light and very cheap to make.
    Such a rig has a mast even shorter than a gaffer, as the foil gaff is sectionally strong enough to dispense with a main halyard located above the gaff's throat. Instead, the halyard is located at the throat itself, which is at masthead height. If side to side stiffening of the gaff is required, a pair of mini-spreaders and a set of diamond stays can be added to the gaff, making sure to locate the spreaders such that they are below contacting the upper shrouds (which means the upper gaff diamond stay terminals are a bit below the gaff's head, maybe a couple of feet).
    The foil gaff sits atop the boom when furled. Even if the mast is lowered, the boom, being stanchion mounted, is unaffected.

    Alan
     
  2. Flumixt
    Joined: Oct 2006
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    Flumixt Junior Member

    Well I drew this up as described (it was fun and took some doing but you write well) and it looks to me like the gaff main is loose footed but 1/2 way between the boom and masthead and even with a very very long boom might be hard to get the right sheeting angle and/or tension from the clew to the boom. I'd bet the foot would bog out too much or would battens fix that? Did you plan to have a telescoping (or similar concept) boom for when the main is lowered to change that sheet angle? Last, why not run the boom from its stanchion directly to the main clew?
     
  3. BWD
    Joined: Aug 2006
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    BWD Senior Member

    Interesting. I imagine the spars could be a tough engineering problem though.
    Then you must get "backstay" and sailcloth in tune with the flex of that floating gaff?
    The idea has appeal, I just wouldn't know how to tackle it.
    Could you post a sketch?
    I too tried drawing this but have no idea if I am really on track with it....
     
  4. alan white
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    alan white Senior Member

    I'm beginning to think words ain't gonna work...
    The boom is normal, could be loose-footed or with slides or lacing.
    The salient design departure is the way the lower luff of the mains'l is hanked to a wire and not a mast. The upper (above gaff throat) luff is attached to a gaff which is shaped like a banana as seen from the side------- the gaff's sectional shape is like a skinny teardrop.
    The stanchion is located where the mast usually exits the cabin roof. It would be as tall as the space between deck and boom on a normal rig. The boom is attached to the aft upper point of the stanchion; a stanchion is used because otherwise the boom would bend the luff wire stay opposite to the boom. This arrangement allows the mast to be lowered without affecting the boom at all. If the mast is planted at the bow, and hinged, it could simply be lowered down to one side of the boom.
    So the mast meets the deck a full third of a boat-length ahead of the wire that's replacing it.
    Much like a gunter, the gaff slides up and down to allow reefing. In the lowest reefed position, the gaff's lower pipe slide (foot) is atop the boom/stanchion juncture, at which point the peak halyard can be uncleated, and release the gaff from the gaff's upper "pipe slide" (of the two pipe slides attaching the gaff to the wire)----- and the gaff pivots and drops onto the boom.
    At this point, simply undoing the forestay from the bowsprit-end would allow the mast to be lowered if it's deck-hinged. I make a point of mentioning the way the mast drops to illustrate how independant it is from the furled sail, boom, and gaff. It is shrouded at a single set of chainplates by six shrouds, three per side, and the chainplates are adjacent to the mains'l luff wire.
    I am going to try to attach a drawing somehow, though I am very bad at "computor", having picked it up somewhat recently.
    Thanks for your interest.

    Regards,

    Alan White
     
  5. alan white
    Joined: Mar 2007
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    alan white Senior Member

    As you can see, BWD, we posted simultaneously---- I only read yours after writing the last.
    You are right that the spar (the gaff) is not going to be your grandmother's familiar wood stick. The mast is easily made of round pipe. The foil-section gaff, however, would have to be at least as stiff as a normal wood gaff athwartship, and far far stiffer fore and aft (though the latter is the easiest to make stiff. I picture a section which would be (30 ft boat) about 2" wide and 12" fore and aft at the masthead height (tapering to 3" at bottom and top). What is wanted is a low turbulance luff, especially high up since this is an elliptical (spitfire wing) sail at the head and so is expected to be considered efficient sail area.
    Keeping the gaff in column is important, mainly at any reef position below full-up and full-reef. Otherwise, stays (or the boom stanchion) are located so as to prevent distortion. A simple running shroud per side (gaff foot) would suffice in the case of middle-reefs if it was found to be a problem, and gaff stiffness could be augmented, as said, by a diamond stay (requiring a short set of spreaders on the gaff itself. A spreader set only perhaps a foot out to each side halfway up the gaff would be adaquate on a 30 ft boat.
    As said, the gaff spreaders may NOT contact the upper shrouds, so must be located below the point where they would otherwise do so. Further, they should always be above where the lower shrouds could hook them.

    A.
     
  6. BWD
    Joined: Aug 2006
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    BWD Senior Member

    Well I quickly sketched some ideas attached below. Took aspect ratio off the traditional version, not sure if that is the shape you were thinking of.

    As far as the gaff, I would look at a thicker section esp up to the throat or else it could get expensive and heavier than needed. Taper it towards the tip. A carbon guy will tell you how much he can taper it.

    I would not try to stop the spar flexing. I see the elliptical sail shape as cutting away excess leech that would be twisted off, rather than adding roach. If you approach this way and match luff curve to spar flex you end up with a low drag sail that twists off smoothly in gusts, reefing less often and needing no diamonds. Like a Tom Wylie cat (or even a windsurfer).

    Sorry if my doodle butchers your idea, especially with regard to AR. I added an alternative to think about with similar shape and goals, but less running and standing rigging. It would lose the ability to wing out boom so far, but carry a bigger spin if you like. Then there is always the traditional rig, prettiest to my eye...
     

    Attached Files:


  7. alan white
    Joined: Mar 2007
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    alan white Senior Member

    Good job! The spreader behind the mast is correct at about 60% up the mast, the sail is right... and I've put the mast right at the extreme end of the bow, while you have it further back--------- without my long bowsprit.
    The primary advantages are low windage aloft (sails down or reefed), and low luff turbulance. The idea was to do this without the "luffstay" being unsupported in the way a jib is over a long span. Instead, the span has been reduced to one third of the overall luff, so rig tensions will not be extreme.
    I also like the fact that the mast is light and handy to drop single-handed on boats below, say, thirty feet, while leaving the boom in place. No crane needed, repairs/inspection can be done at sea, etc..

    Thanks again for going to the trouble. Remains to be seen if this rig performs well.

    Alan
     
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