This has influences from several rigs and I am left wondering what to call it.

You can see it involves a tilting mast not unlike a crab claw or Gibbons/Dierking sail, but there is a gaff-type sail (here represented by the Wharram wing sail). I don’t see any reason this cannot be reefed like a gaff, and it should operate much like a Gibbons/Dierking sail; in fact it is virtually much like the upper half of a Gibbons/Dierking sail. A happy result of this mashup is the aerodynamic force per sail area can be lower than with a Gibbons/Dierking sail.

I chose to render (forgive the sloppy rendering) this with a Wharram wing sail for two reasons:
1) to imply that this can of course have battens, perhaps notching up the perfomance over a simpler gaff sail.
2) to imply a boomless sail. The Wharram wing sail is boomless, as you may know. This seems critical to this design, such that the illustrated geometry can be used and that the boom does not cause problems during shunting. During shunting, when the sail passes from one bow to the other, the boomless sail can weather-cock without an angled-boom fighting against gravity and getting in the way of the shunting process. The alternative to this gravity problem is a wind-surfer type boom (cannot be reefed then) or compromise the low aerodynamic center of effort to place a boom.

So, if you’ve read this far, what do you think? Is this a leap forward in proa technology or a lead balloon?

If we take this rig down the road of simplification, doing away with the tilting mast, another interesting design immerges.

The orange line represents the last batten; below this the sail is only supported by the line running from the top of the mast to the bow ( the line that is released when shunting) and by the sheet. Thus the sail can go slack during shunts to get over the hull and to the other bow even though it is longer than the mast is high. Green represents what would be the mast of the typical gaff or in this case the yard (I think).

This design is amenable to a free-standing mast so I have it illustrated (poorly) that way here for simplicity.

Edit: This design is easier for me to name: I would call it a “gaffed jib” which reefs as a gaff would instead of roller reefing.

Adam - 05 June 2012 06:10 PM

During shunting, when the sail passes from one bow to the other, the boomless sail can weather-cock without an angled-boom fighting against gravity and getting in the way of the shunting process. The alternative to this gravity problem is a wind-surfer type boom (cannot be reefed then) or compromise the low aerodynamic center of effort to place a boom.

I don’t understand why you expect a difference between a wishbone boom at a right angle to the stay and a boom at another angle.  If the axis around which the sail rotates is vertical (i.e. if you set it on a vertical mast), then the boom and sail stay at the same height during rotation, no matter what the angle of the boom to the luff of the sail.  If the rotation axis is angled, as your stay is, any boom will tend to fall down in light wind, no matter what its angle to the luff.

Without a boom, how will you get hold of the clew to reef?  The gaff prevents you from rolling the sail around the stay, so I expect you are thinking of slab reefing.  You can’t set up permanent reefing lines because the line from the clew to the reef point has to go forward to the tack.  Without a boom to take the compression, that would rather mess up the shape.  I think you’d have to drop the sail most of the way, enough so that you can sheet in the lower part of the sail without powering up, then pull the leech in by hand, tie up the bit you have reefed away, and either tie the clew to the next reef point or move the sheet.  The sail is likely to be flogging at the time, and it is a relatively large sail.

A boomless sail without the wide sheeting base of a catamaran or trimaran also tends to have a poor shape when going downwind.

I think you’d get more trouble from omitting the boom than from keeping it.

Regards

Robert Biegler

Adam - 05 June 2012 06:10 PM

During shunting, when the sail passes from one bow to the other, the boomless sail can weather-cock without an angled-boom fighting against gravity and getting in the way of the shunting process. The alternative to this gravity problem is a wind-surfer type boom (cannot be reefed then) or compromise the low aerodynamic center of effort to place a boom.

Hi Adam,
maybe I overlooked something, but I don´t see why this kind of sail should not be reefable?
And a wishbone boom would angle downwards. See attached:

Best regards

P.S: And trimmed as well…

I don’t understand why you expect a difference between a wishbone boom at a right angle to the stay and a boom at another angle.

When the luff hangs down vertically during a shunt, a boom that starts horizontal during sailing will angle up where it would rather not be. If it starts angled down at a right angle to the luff during sailing as you and Steen mention then this wouldn’t be a problem.

Without a boom, how will you get hold of the clew to reef?

I think you are describing what I had envisioned, Steen’s diagrams show it as well.

A boomless sail without the wide sheeting base of a catamaran or trimaran also tends to have a poor shape when going downwind.

Good point. The leeward pod often included into a pacific proa would help some, perhaps an extension on the pod for attaching the sheet would be in order.

I think you’d get more trouble from omitting the boom than from keeping it.

I think you are right. Thanks very much for your insight.

Steen, I had not seen that type of sail reef before and didn’t realize it could. A wishbone boom would seem to work nicely then to avoid a “bad tack” if the boom was only on one side of the sail as the diagram seems to represent. I wonder if that type of sail would still work to have the yard end at the wishbone boom so the sail could be taller than the mast? And forgive my ignorance, but what is this sail called? It is very similar to what I had in mind.

Adam - 06 June 2012 10:50 AM

When the luff hangs down vertically during a shunt, a boom that starts horizontal during sailing will angle up where it would rather not be. If it starts angled down at a right angle to the luff during sailing as you and Steen mention then this wouldn’t be a problem.

I finally understand why you say the boom rises, but I still don’t get why the angle to the luff should make a difference.  If you compare the position of the clew while sailing to the position while the sail is midships during the shunt, then because the angle of the luff changes, so does the angle of the boom.  However, no matter whether you have a boom along the foot or a wishbone boom at a right angle to the luff, if the clew is in the same place with both booms while sailing, it will be in the same place with both booms when halfway through a shunt (treating the sail’s plan form as constant for the moment).

Actually, if you were to use a wishbone boom, I think you should have a solid spar at its front end.  Wishbone booms have been used on staysails, but only with a fixed stay.  If you want to attach a wishbone boom to a stay that you let loose for shunting, with a flogging sail attached, I’ll watch from shore or another boat, and salute you if that weight loosely attached to the boat but tightly attached to the flogging sail remains under control.  A conventional boom wouldn’t control sail twist so nicely, but it would have a lot less play if it and the stay are attached to a slider in a track.

Until the rotation axis is vertical, the weight of the boom tends to pull the sail in a bit.  I think that is what you want to avoid.  To find out whether it is a problem, ask the people who have experience with crab claw sails.  Those have exactly the same feature.

As for reefing with a wishbone boom, have a look at http://www.wyliecat.com/.

Regards

Robert Biegler

This is why the masts of Asian junk-syle craft were often canted forward… so that the weight of the sail, battens and spars would tend to draw the sail outboard.  Perhaps some degree of leeward cant on a proa might help to offset the crab claw-like inclination(!) to collapse inboard as the wind fades?

I finally understand why you say the boom rises, but I still don’t get why the angle to the luff should make a difference.

I did some sketching, and you are right. If the boom rises on one type of boom during shunting it will rise on the other regardless of angles. There is a geometry that makes so the center-of-mass rise of the boom is zero (on either type of boom) as shown. The “balanced” figure I drew with the green line through the center of the boom seems to show the sail would not complain too much about being in the shunting position. A full length yard being led along a track would seem to secure that rig nicely during shunting.

Actually, if you were to use a wishbone boom, I think you should have a solid spar at its front end.Wishbone booms have been used on staysails, but only with a fixed stay.  If you want to attach a wishbone boom to a stay that you let loose for shunting, with a flogging sail attached, I’ll watch from shore or another boat, and salute you if that weight loosely attached to the boat but tightly attached to the flogging sail remains under control. 

Until the rotation axis is vertical, the weight of the boom tends to pull the sail in a bit.  I think that is what you want to avoid.  To find out whether it is a problem, ask the people who have experience with crab claw sails.  Those have exactly the same feature.

Good points! Perhaps part of the solution is to use a track for the leading edge of the boom as you mentioned. Or, perhaps you could have the yard go the full length of the sail and let the leading edge of the boom and bottom of the yard “go for a drink” during shunts. This might dampen out flogging and awkwardness; the proa needs to be stopped during shunting anyway! As for the sail wanting to pull in due to gravity, perhaps MTPs suggestion would work during shunts along with the track helping out, and/or a sheet pulley outboard of the lee pod might be in order to prevent the sail from falling in unwantedly during sailing and shunting. A happy result of that arrangement is that the weight of the sail itself is reducing the load on the sheet while sailing in heavy air.

I just realized that in a way, all of this re-tweaking is making this rig work and look quite a bit like Mark Belvedere’s proa rig! The biggest difference is proportions making his mast become this proa’s yard.

http://www.amazon.com/Flying-Sails-King-Tonga/dp/B004N6YJPE/ref=sr_1_1?s=movies-tv&ie=UTF8&qid=1339023646&sr=1-1
http://www.kaliafoundation.org/speedtrial.htm

If you add reefing to M. Schacht’s Pookie rig, that’s not too far different than what we’re talking about either.

http://www.proafile.com/archive/article/teh_pookie

Perhaps the biggest question I have here is can swinging the bottom of the sail replace the need for tilting the mast/supports to keep aerodynamic center of effort forward? It appears, yes. Is that more “convenient” to build and operate than a tilting mast solution?

One possible result of this discussion on a model not unlike Madness. The lee pod gets in the way but is not insurmountable. The solution seems to be a rubrail here to let the yard get over the pod. With some changes in geometry, the rubrail could become the cross beams and the lee pod itself; that might lend itself toward some more pleasing lines than slapping a blue hula-hoop onto a proa.

Pros of this rig:
-The center of effort is just windward of the main hull in nearly all sailing positions
-Reefable
-Shuntable
-Appears to be simpler to operate than a rig involving a tilting mast
-Appears the rig dosn’t need to ever swing above the cockpit

Cons:
-Complexity of building and maintaining a rubrail: perhaps can be lessened in future renditions
-During shunting, the sail may want to fall in during light airs; EDIT: Just let the mast be a few feet higher and the yard be the length as shown and it will slide over the TOP of the pod and this is fixable.
-EDIT: where do the stays go?

Neat!  Maybe with a bit of geometry thrown into it all the rub rail can be changed to a track and the butt end of the yard (or luff spar?) is car-mounted?  It would be easier to handle during maneuvers and shouldn’t be as likely to get out of hand. Moveable sheeting points could be similarly car-mounted.

The lee pod makes a natural extension to the deck to support the leeward quadrant of the track, and rearranging the crossmembers further fore and aft might provide convenient bearing points for the windward track ends.

I seem to remember seeingimages of a smaller beach-cat sized proa somewhere that had a crab-claw rig running on a track along the lee gunwhale though I’m sure that I ever found out how successful it was in practice.

MTP - 07 June 2012 03:55 PM

I seem to remember seeingimages of a smaller beach-cat sized proa somewhere that had a crab-claw rig running on a track along the lee gunwhale though I’m sure that I ever found out how successful it was in practice.

You might be thinking of Teh Pookie?
http://www.proafile.com/archive/article/teh_pookie

Edit:Gaia’s Dream works with a track to slide the mast along, though the sail is attached to that mast instead of a separate spar.
http://www.youtube.com/watch?v=iS270ousYwg&feature=related

Car mounted sheet sounds like it would work very well for this.

I just realized that this design does not allow much in the way of stays. As it is drawn now, it might as well be a free-standing wing sail, or a wing sail with two windward stays, and avoid this complexity. Perhaps the rub rail or track should be expanded a bit and the luff spar left to go somewhat leeward of the mast during shunts.