Easy to reef - Gibbons rig. Video.
Hi everybody!
I got this idea about an easy to reef Gibbons rig.
I made a VERY crude simple mockup with some plastic pipes and cable-ties. It does not work yet, but i will build a working rig along these lines soon.
I was thinking about the Ljungström-rig with its rotating mast, where you reef the sail by wraping it around the mast as many times (by rotating the mast) as necessary to get the desired sailarea.
A very simple way of furling the sail. The large diameter mast is needed to get a good aerofoil. Since the sail is partly wrapped around the mast one gets a very aerodynamic shape of the leading edge. Fredrik Ljungström did a lot of wind-tunnel tests of these in the late 40ies. He fund that they were very similar in lift/drag as a solid aeroplane wind of the times.
My idea is that one makes the yard like a large diameter straight mast with the three-sided sail split down the middle, where it will overlap the boom. There is a wheel in the middle of the yard that is used to turn the yard to reef the sail.
I hope my pictures gives a better explaination than my crude english.
I will build a working rig as soon as i get the strenght to do it.
Cheers
Johannes
This is how the sail (blue) and the boom (green) should be. That way the gap between the two halves of the sail is covered by the boom.
I hope this makes sense.
Cheers
Johannes
That is a nice idea. The only Gibbons style rig I’ve seen was Kevin O’Neill’s humongous rig on Skate before he switched to a much more controllable schooner rig. I never actually got on the boat, there was always a chance the wind might pick up beyond the 6-7 mph that the boat fairly flew in and I’m a coward at heart.
Kevin’s rig and Gary Dierkings (who Kevin consulted) had spars or battens toward the ends of the span but it may well be that a simpler triangular planform that is reefable could be a winner, particularly when the wind picks up.
cheers,
Skip
That is clever. The CE does not move as much when reefing as it does with a vertical mast.
I think there would still losses through the slit in the sail, since wind will force the sail to fill and stretch away from the boom.
You could possibly sew in a zipper into the slit, and tie the zipper pull to the boom right behind the yard. That way, it could automatically zip/unzip when reefing or letting the sail out.
I think there would still losses through the slit in the sail, since wind will force the sail to fill and stretch away from the boom.
I imagine the sail would be in something similar to a mast-channel (where the luff of the sail attaches to the mast in a Bermudan rig). It should not be able to leave the groove in the boom.
Thanks for encouragement. I hope i can use this kind of rig on my Advanced Sharpie Proa.
Cheers
Johannes
Interesting idea, Johannes.
I first thought you had drawn one half of John Marples Diamond Rig concept until I realized you are proposing furling around the spar. I’ll still post this for contrast at least.
This is the cross-section the boom should have. There should be some rope sewn to the side of the sail that will run inside the hollow groove. I hope that will be enough to stop any air from leaking through.
The boom should be pre-bent to give the sail a good aerodynamic shape.
Cheers
Johannes
Hi Johannes,
I tried the Gibbons rig on my first proa P5 about 10 years ago. Like Kevin I changed later on other proas to “better” rigs. The main problem with the Gibbbons is the large drag on topp during the shunting maneuver. It could handled with small sail area under good conditions, but at stronger wind it becomes fast a problem. I reported about my sailing experiences with the Gibbons at: http://www.multihull.de/proa/p5/p5sailgb.htm
I am also thought about reefing systems for that rig, and get another solution. Not rolling up the sail on the mast, but using the boom. Therewith you can’t reef partially, hence I would use a wing mast as ‘storm sail’, if the soft sail is rolled up.
Another solution is the rig of Wilhelm Prenninger (similar to a Gibbons), who combined two surfsails with a sophisticated folding mechanism. He reported about in my Multihull Form, Proa Section (sorrily only in German).
However, IMHO the Gibbons rig is at last only a play tool for small proas, sailing on a lake.
Othmar
Only to show the next picture ...
Thank you for great information and your first hand experience Othmar!
I read about your experience through the link you posted. I understand the Gibbons is a handfull to handle in stronger winds. I hope that a heavier boat and spars, together with a easily reefable Gibbons will calm it down a bit.
In really strong winds i might have to furl the sail completly each shunt, but that should be fairly quick and simple with the ruller-furling. I will have to test it with a model and work out all the details before i commit to a large sail.
I believe there is some seriouse potential in this type of sail. With a simple method of reefing and potentially fast shunting it should be THE proa-rig. More “horsepower” usually makes it more difficult to control.
Cheers
Johannes
The Gibbons rig concept isn’t too far removed from having a very short-tethered kite which hangs in a neutral postion from the top of the mast when it’s not being pulled into action by control lines from deck level. Maybe the weight and complexity of additional spars and reefing gear can be replaced by simply having a selection of bigger and smaller of soft kites with inflatable leading edged stuffed in bags onboard?
“Hey, Johannes…. it’s a big blue sail day, don’t you think?”
“No, Othmar. The wind is going to pick up later, so we best stick with the little yellow sail today!”
The mast needn’t be overly strong as all of the driving forces are direct from the kite to the deck… it is really just there as a sail launching and docking device just like the gantries used to ground dirigibles.
I think kites can be very very effecient sails, but they are a bit over my head (pun intended) at the moment. I kind of like having the sail(s) attached to some kind of yard and/or mast. I have to limit my area of experiment, even though its very educative to test things in real life.
I have been reading through some Ayrs Catalyst. In number 33 january 2009, there is an article about delta-shaped sails. http://www.ayrs.org/Catalyst_N33_Jan_2009.pdf
I think there is a lot of potential in this kind of sail. I think its important that a cruising Proa has a sail that is very forgiving of sheeting angles and tolerant of different angles to the wind in general. A delta-shaped sail seems to be the perfect sail in this regard.
Cheers
Johannes
I have been working slowly on this reefable Gibbons rig. Due to the small size things tend to get very unwieldy and coarse, but it seems to work like it should. Now i will start with the actual sail.
I have been through a couple of revisions already. It should be much easier on a full size rig. I don’t have the tools to build very small, light and strong structures.
I hope this gives a better veiw of the rig.
Cheers
Johannes
On the full size version of this rig i will have a sleeve around the mast so i can adjust the height of the yard. That is a way to adjust the CE to suit any windstrength and load on the boat. If the yard is higher up on the mast it will have a steeper angle and the CE will move forward. If reefed the CE will move even more forward, but that will be easy to adjust back by lowering the yard a little bit. This makes it easy to adjust CE and the amount of lift the sail has on the bow regardless of windstrength. I think its important to have the possibility to adjust both CE, yard-angle, boom-angle and the sail-area gradual over a very range.
I have not made any more progress today. I have been reading about surfboards and sketching on possible variations of this rig. Im thinking about dividing the sail into three different parts… “To many mind!” as Nobutada in the last samurai would have said.
Johannes.
Terry Rempel said:
A sraight yard would allow rotation to shorten or reef the sail. The luff curve could be maintained by allowing the boom to slide through a sleeve in the sail and be stayed by a line lock on the boom end. This would allow sail tension to be reset after reefing and not affect the luff curve significantly as the boom end has the least curve. The yard center could be held in a loop around a grooved center bushing slid onto the yard and the groove would rest tight to the mast top. Rotation would be achieved by a line wrapped around the yard center and stayed to the mast head in another line lock. Mechanical advantage may be obtained by the use of a pulley on the yard to distance the line out from the center of the yard making reefing easier. The process would be straightforward
Posted: 26 Jul 2011
I found this in the comment section in the Proafile article on the Gibbons rig.
Soo much for being original and creative… I guess it is hard to think of something new in this field…. There is soo much people interested in sailing. Somebody somewhere has already thought of it all…
Johannes
Today I finaly have a sailable version of this reefable Gibbons/Dierking - rig.
Just a picture. The other picture shows why there is no video today… It forgot to attach the skates to my monoproa…
Cheers,
Johannes