Lug rig adjustable CE
I have decided to start a new topic rather than keep hijacking Snelson’s Canoe.
See picture below
Offset balanced lug rig with adjustable CE, needs 3D physical models to develop it further but I thought I would put it out there.
The green strut is able to rotate around the axis of the mast, but its ends are free to seesaw with a fulcrum at the mast. Tension on the yellow line (a) pulls up the end of the green strut (b) forcing down end (c) tensioning the lug sail in the normal way, down haul would be located at (c) conventionally. If the purple line (d) is pulled in (to windward) the CE moves forward and windward, if released aft and leeward.
This also helps in off wind situations very much like a balstrom rig keeping the CE inboard but also gives control of its position.
Shunting like the offset rig developed by Beeton in ‘69.
I realise lots of work needed on the precise geometry and stresses / deflections involved
TINK
OK, now I get it! Very interesting! THAT’s how its similar to the spinnaclaw.
In a shunt, does the green thing flip around, and the sail stays on the leeward side?
Now I’m going to steal this idea but substitute a windsurfer rig. Remove the boom. Bring the yard all the way down to the green thing. Now all of the green thing that’s behind the mast can go away, because its no longer adding luff tension. Add a wishbone boom to the yard, terminating in the clew. Voila—Spinnasurfer. You could also see this version as the lovechild of Te Pookie and Spinnaclaw.
Good thinking, Tink.
chris
Yes, it needed a 3d picture to get the idea out of my head and give any one else a chance of understanding my waffling. As I have said this needs so real modelling to understand the geometry properly something I am frustratedly unable to do at the moment. Yes the the sail end of green thing flips round leaving the sail to leeward.
I keep going around in circles with proas, somewhere I have very similar sketch I did 30 years ago, and I remember modelling it.
I like the Spinnasurfer idea, the thing I don’t know with both ideas as as the bottom half of the sail goes forward the portion above the halyard connection goes backwards. What the net effect of the CE movement needs investigation.
I have a document called Optimum with Te Pookie and Spinnaclaw on the same page.
Anyway I’ll carry on sketching
TINK
Here’s a Spinasurfer visual prototype.
The spinaker pole (between mast and the base of the windsurfer rig) has a snotter to the mast, like a sprit boom. So that length will be somewhat adjustable. There are two lines that haul the tip of the spinaker pole to windward—one for each shunt. Then I think you have two sheets on the wishbone booms—one for each shunt. That should give you LOTS of options in terms of where you place the tack of the windsurfer rig, and how you sheet it after that.
This sail is 100sq the same as for the canted jib only version of this boat.
on a reach…
Really like it,
Below not as sophisticated as your CAD but I think it shows the basic idea has some legs, the high clew of the windsurfer helps.
I Like the snotter idea. The windsurfer rig means the pole does not need to be forced down which is a great help.
Looking at below I would have liked the CE to get ahead of the mast. In that way with a single board in line with mast a simple sail steering system would work. If the board pivoted you could get CE ahead of CLR when required.
Have you spotted that I don’t like rudders yet.
TINK
Ah rudders…
If you add one more control to the spinnasurfer you should have LOTS of control over CE (fore aft AND side to side).
That would be a track on the windsurfer rig to adjust the point it intersects the mast.
My concern with the lugs is keeping the luff tight—but that should be surmountable.
best,
chris
Looking a the purple picture shows a lot of potential, I am seeing total ballance down wind. I think what you are saying is the mast end of the pole is on a track, as you move it up and down you get that great control.
I now realise that if you have a tall mast and the windsurfer mast connected closer to the head you get the CE as far forward as you want.
TINK
I now realise that if you have a tall mast and the windsurfer mast connected closer to the head you get the CE as far forward as you want.
Might interfere with the sail shape though, if it changes the bending characteristics of the windsurf mast.
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.
If you want more elegance, replace the gallows by a bent mast. Or replace gallows and spar by a crescent attached to a shorter rotating mast. The windsurfer rig is attached to the ends of the crescent. Could be done with a lug rig, too, but then the crescent has to take higher bending loads. You’d carry a big bow, with the lug sail as the bow string. And once on the beach, you could always convert the bow into a big siege engine. If you want to avoid attracting the interest of Homeland Security, perhaps you’re better off with the windsurfer.
Regards
Robert Biegler
Yes, it needed a 3d picture to get the idea out of my head and give any one else a chance of understanding my waffling. As I have said this needs so real modelling to understand the geometry properly something I am frustratedly unable to do at the moment. Yes the the sail end of green thing flips round leaving the sail to leeward.
TINK
Not to disparage the 3D modelling, I made a part of my living doing same 20+ years ago, but a reasonably quick and dirty real model to sit on your desk to contemplate has much to recommend it. I’m leery of extrapolating model test to full size but being able to poke at bits and look at then from different angles is part of our heritage.
Skip
Dear Skip
100% agree I too have spent time in the past, as we call it here, as a ‘CAD jockey’ but there is no substitute for getting up and making a real model. The dirtier the better in my book; tape, string and a few bamboo skewers would do. Spending hours on a model can warp your thought patterns and you end up convincing yourself something is good that may be isn’t.
Frustratingly with one arm in a sling at the moment that option is not feasible but it is only temporary and summers on its way.
TINK
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.
Dear Robert
I had started this idea off in the Snelson’s Canoe topic just as an idea for an offset lug rig. I have reposted, for neatness, below some of the mast configurations that it could have, I am sure there are more.
I did think of rotating the whole mast including crane / gallows but thought the forces involved would be extreme
Anyway will carry on sketching
TINK
Not sure where this is going.
I have put curve in the boom so it doesn’t hit the water when pulled forward.
For the minimal proa with its small sail area and a high peaked yard the luff will be relatively short and hopefully it will keep tight
TINK
Hi TINK,
I don’t see how the boom would hit the water even if it was horizontal.
So long as the distance from the lower pivot point (on the boom) to the mast is greater than the distance of the upper pivot point (on the yard i.e. the gallows length) is from the mast, the boom will incline upwards during the shunt.
The potential problem that I see is not having enough clearance so that the forward ends of the boom and the yard striking either the mast or the lower articulating arm. The gallows needs to be long enough to allow clearance for the yard and the lower articulating arm (for want of a better word) may need to be curved or inclined slightly upwards from the mast to the boom. I hope my description makes sense!
Hi TINK,
I don’t see how the boom would hit the water even if it was horizontal.So long as the distance from the lower pivot point (on the boom) to the mast is greater than the distance of the upper pivot point (on the yard i.e. the gallows length) is from the mast, the boom will incline upwards during the shunt.
The potential problem that I see is not having enough clearance so that the forward ends of the boom and the yard striking either the mast or the lower articulating arm. The gallows needs to be long enough to allow clearance for the yard and the lower articulating arm (for want of a better word) may need to be curved or inclined slightly upwards from the mast to the boom. I hope my description makes sense!
All makes total sense, I need to start working on some scale drawings and a physical model
TINK