Lug rig adjustable CE
An ingenoius method of having a balanced rig with the mast always to windward and therefore good sail shape. Could work well on your beach-proa. For a cruiser, the ease of reefing, as with a Junk-rig, would be more dificult to achieve.
Mark
Hey Tink,
I like the cantilevered lug rig idea. Its low. Its simple (in theory). Its kinda salty looking and futuristic at the same time.
My concern about this rig is the same one I have about the Snelson’s Canoe rig—luff tension.
With the lug rig, the tension in the halyard shared between luff and leech, in proportion to the position of the halyard on the yard (and outhaul on the boom). So that halyard/downhaul combo needs to be CRAZY tight. Now you’re taking that tension and holding it at a distance from the spar that provides the tension. On a lug rig the halyard tension is just inches from the spar. In your rig its feet.
Another worry is reefing. So it starts to blow. Hard. You ease the sheet(s) and lower the halyard. Now the whole lug rig is swinging around on the halyard like a big angry kite—yards and booms trying to knock you out. At least with a regular lug, the yard is attached to the mast so that its just pivoting.
But maybe I’m missing something?
Keep the ideas coming,
Chris
You could instead revive the gallows of the lug rig version and align it with the spar of the windsurf version. let the whole shebang rotate together. The whole sail will move.
I had the realisation that the concepts above have a bit of a flaw in them if you want to steer. As you try and move the sail forwards and back the whole sail has to get longer, and that just isn’t practical or you start with a floppy luff!
So I had this idea and it follows on from Robert’s comment above, make it all rotate.
This one is a little like the pyramid rig (J Manners-Spencer AYRS airs 8 1974) but single lug sail and three struts rather than four.
In the sketch below the
Orange arrow is direction of travel
Yellow lines are tension wires
Blue lines compression struts
Red lines boom and yard
Purple line luff and leach
One of the compression struts is the gallows so that the lug sail can swing through 180 degrees presenting two sides with un disturbed air flow, ignoring wind shadow from rigging.
The sail would require two lightly loaded main sheets, normal proa set up
Then by rotating the mast the CE of the sail would be moved forward or backwards as required giving control of the CE relative to the CLR. I think that if a line was connected to the boom strut and pulled in the direction of the bow this would work, the question is what force is required.
This is intended of an 8sq m sail on my minimal proa not an ocean crossing craft. The mast would be free standing and mounted in simple bearings. The tension wires allow for the gallows stresses while keeping the mast nicely in column and a relatively small diameter, with a good peak to the yard it isn’t too tall anyway.
It’s a work in progress, hope it makes sense.
TINK
I love a bit of theory-crafting as much as anyone else but it’s getting a bit carried away, don’t you think? For a while it was kind of fun watching you collectively Rube Goldberg your way towards reinventing the crabclaw… but when you’re proposing using 9 spars and upwards of twenty lines to control a single sail something is going wrong.
Proas are all about the simplicity of their design and minimal loading of their structures, after all….
I love a bit of theory-crafting as much as anyone else but it’s getting a bit carried away, don’t you think? For a while it was kind of fun watching you collectively Rube Goldberg your way towards reinventing the crabclaw… but when you’re proposing using 9 spars and upwards of twenty lines to control a single sail something is going wrong.
Proas are all about the simplicity of their design and minimal loading of their structures, after all….
I don’t mind Rube Goldberging, just keeping the brain ticking over. I do find things get complex before you get to a final solution.
I think my drawing may be more complex than it looks, most of the spars are little more than spreaders and the lines standing rigging. This lot never needs touching after the first set up. The only lines that are used during sailing are the twin main sheets, as used on most proas. There are then two simple lines for steering only one to be used on each shunt. Lines have the advantage that they can be accessed anywhere on the craft.
So yes in isolation Mr Goldberg may be proud but in the big picture no rudders / steering paddles, mast strut, pivoting mast and all the associated rigging to move it all from one end to other. Before I get all sorts of posts I have total respect for the simplicity and innovation of traditional proas.
Anyway it is just a work in progress
TINK
Getting simpler
This whole lot is free to turn 360 degrees,
The only other things you need are
1 vaka
2 aka
1 ama
1 leeboard / dagger board
Green lines for sheet and steer would be repeated for other direction hence x2
Still a work in progress for a minimal proa 8sq m sail
TINK
Mmmmm….nice.
I don’t have the same aversion to rudders, having found them to be far superior to steering oars at a certain size. Anyone that can barrel downwind without a rudder has my admiration.
But, I may have to copy the rigging and gantry stuff as a trial, looks pretty elegant.
cheers,
Skip
Yes, getting simpler TINK. But I’d add a couple of struts (or lines) from the end of the ‘gallows’, from which the yard is suspended, back to the ends of the stays behind the mast. This would then describe a triangle and stop the gallows from bending (and breaking) from forces f&a from the sail. It would also complete a tetrahedron (which is the ultimate structure for stability) with the lines above this triangle.
I would also arrange the yard to be as close as possible to the end of the gallows to minimise the movement of the yard resulting from sail forces. I think this would be a problem otherwise. The problem doesn’t go away unfortunately when the sail is reefed. In fact, it would get worse. At least that is how I’m seeing it.
Getting closer though 😊
Very dirty cad model on minimal proa, 7sq m of sail visually any more looked scary. Still a work in progress but the bottom gallows needs a bit of work the foot of the sail is 400mm above where I would like it. This obviously moves everything skyward and increases heeling for zero gain. Luff is only 2400mm which is good for tension.
TINK
Yes, getting simpler TINK. But I’d add a couple of struts (or lines) from the end of the ‘gallows’, from which the yard is suspended, back to the ends of the stays behind the mast. This would then describe a triangle and stop the gallows from bending (and breaking) from forces f&a from the sail. It would also complete a tetrahedron (which is the ultimate structure for stability) with the lines above this triangle.
I would also arrange the yard to be as close as possible to the end of the gallows to minimise the movement of the yard resulting from sail forces. I think this would be a problem otherwise. The problem doesn’t go away unfortunately when the sail is reefed. In fact, it would get worse. At least that is how I’m seeing it.
Getting closer though 😊
No, that is not what I meant. The ends of the three compression struts radiating out from the mast need to be connected to stop them moving horizontally. You had the windward two connected in your previous drawing - include the third one which is the gallows.
The extra line you have added to the gallows down to the mast is not necessary (it will foul the yard in any case). The vertical restraint is furnished by the sail to the lower gallows.
I hope this makes sense!
Think I’ve got it now, I am not sure of scantlings or materials yet but had envisaged the gallows and the compression strut fabricated as one part well secured to the mast.
I appreciate also the compression struts aren’t at the correct angle bisecting the the vertical stays.
Tink
I’m guessing that you’re going to need another set of diamond wires to stiffen the mast as well—so the spreaders would be in the middle of the mast, with wires going to the ends.
Slight change of tack for the Spinnalug. Rather than trying to rigidly attach the gallows to the mast it is now completely free to rotate up and down. In the sketch there is an upper and lower gallows (0range) and they can both rotate independently to the mast ‘arrows a’.The yellow line (c) connecting the two gallows counteracted by the sail forces keep the two gallows at the same angle to each other. The other yellow line ( d) with a block controls the gallows up and down angle.
The gallows are subject to bending and obvious need to be able to resist this, for my 7sq m sail they are a total of 1.2 meter long. They can be considered a little like the yard and boom of a lug rig only putting compression forces on the mast. The sail obviously creates the normal bending forces (b) on the mast. As before this whole unit rotates to control CE
The crane below would have the same force diagram
TINK
This all seems overly complex for such a small boat…....
Why not just can’t the mast from the beams over the hull?