View Full Version : gunter rigs and mast chafe
04-27-2003, 11:45 PM
getting around to building my rig soon.
This will be a batwing rig, which uses a gunter.
Much like illustrated here:
EDIT: larger picture with more detail posted below
I was wondering what's the best way to fight chafe on the mast. I plan on finishing my mast bright.
Shall I forgo the varnish and just keep it all oiled with mineral oil ( or other )
I do still plan on coating everything in epoxy.
Since the outriggers telescope out, I plan on a similar arrangement for the crossbeams.
I did see an interesting gunter at the Maine Boatbuilders show. They used a metal track and affixed the gunter to that, but I really wanted to go with the above setup.
[ 04-28-2003, 08:33 PM: Message edited by: brian.cunningham ]
04-27-2003, 11:57 PM
My Drascombe Lugger has a gaff jaw of galvanized steel, covered with a soft plastic sleeve. The same thing could be accomplished with oak and leather. You're worried about the chafe where the jaw sits on the spar? I suppose you could leather that area too, if you did it arfully, tapering the leather so the jaw rode smoothly on hoisting. Sewing the leather, like with an oar, rather than tacking it would be in order.
Edit: On further reflection, a properly leathered gaff jaw would obviate the need for leather on the the spar.
[ 04-28-2003, 12:04 AM: Message edited by: ishmael ]
04-28-2003, 08:06 AM
The sliding gunter rig Brian shows is from Tiphys's practical canoeing.
MOre here: http://www2.friend.ly.net/~dadadata/odd/tiphys.html#simple%20batwing
BRian, I'm not sure you'd want to mount leathers inside those brass rings. I'm not speaking from experience, but it seems to me leather might interfere with the sliding mechanism (especially when wet). I imagine you'll need need to raise and lower this rig from a sitting position, using just the halyard and downhaul. It had better be slick.
I guess I'd be inclined to give the mast an oil finish, as you say...quickly replenished, as necessary.
But I've never used a sliding gunter, so I'm only speculating.
Do you plan to make your own hardware, or have it made to order? I imagine Robert Lavertue of Springfield Fan Centerboard can supply that sort of thing (I believe he's at: 413-783-5589).
I'd be very interested to see how you go about it.
04-28-2003, 08:20 AM
Sorry I didn't look as closely as I should have.
I think leather could be sewn on those rings, and the mast varnished, and it would work fine. An occasional wipe with some beeswax on the leather. Would look sharp. However, this is just a guess.
04-28-2003, 08:30 PM
There's two types show. The top one is brass.
The bottom is actually wood.
The one on the bottom lowers the gunter on a hinge towards the boom.
On either the jaws are hinged.
I'll be brailing mine up to the mast via lazyjacks.
I'd like to take a crack at making it all myself.
If I used round spars I could fit the same size PVC pipes that are going serving as the mast step.
Be easier with square dimentional lumber, 16 footer can be had at the local lumber yard.
I could used dimementional lumber for the spars are well, but that would make for a really flat sail, like the original batwings. In Parker's book he used PVC pipe with wooden dowels in the last 2/3 to give it an airfoil shape. Bawing spars sit in full-length pockets, so appearence is not a factor.
Perhaps oiled leather inside the "irons"?
Or laminate plastic on the inside?
[ 04-28-2003, 08:32 PM: Message edited by: brian.cunningham ]
04-29-2003, 04:03 AM
Though leather gives a nice cushion, it can often be kind of sticky, especially against a varnished mast. In the past, leather-covered jaws were greased with tallow so that they would slide on the spars. Greasing the leather on a small cartop boat is likely to be a big mess just waiting to happen and sooner or later, your sail is going to wind-up with big grease spots on it. Oiling the leather will probably just make it stick more.
I'd be inclined to get out the contact cement and face the working part of the leather with something that slides better on varnished wood, like felt or scraps of Dacron. Some sort of slippery plastic would probably also work.
As far as the sail battens go, I think you will find that the PVC tubes partially stuffed with dowels are pretty inefficient and will probably be heavier than similar-sized battens made from wood. Round battens also tend to present annoying attachment and adjustment problems at their ends as well as make pretty big bumps in the sail that the air has to flow over. Ripping a strip and tapering it down with a plane or belt sander until it flexes the way you want is pretty easy. If you plan to step on your battens, I can see a case for PVC, but if you are seriously interested is shaping the sail, wood is pretty hard to top. In any case, if you intend to induce a constant airfoil camber in a bat-wing, much of it needs to be done with luff curve and broadseaming. The battens are mostly just there to hold the shape.
Just curious, but what are you trying to achieve by forcing a lot of camber into a bat-wing?
[ 04-29-2003, 04:04 AM: Message edited by: Todd Bradshaw ]
04-29-2003, 11:48 PM
Thanks for the latest link. The old one had an annoying pop-up so I didn't link it in.
I want a better airfoil, traditional Batwings are flat. I don't plan on cutting the sails the traditional way, flat, the battens will help not force the shape. I want to get the performance of a modern multihull rig with full length battens..
but with traditional looks, reefing ability, and with the gunter, take-down ability.
I thought about shaping wooden battens as you described. Real easy to put the shape where I want it. I'm affraid of chafe inside the pockets.
[ 04-29-2003, 11:52 PM: Message edited by: brian.cunningham ]
04-30-2003, 04:24 AM
Though they are cut flat, bat-wings are not really flat in use (unlike junk sails which are purposely heavily battened to be about as flat as possible at all times). Wind pressure will put some draft and twist into a bat-wing though the flat cut will often tend to give them a pretty shallow leading edge entry curve, which can make them very intolerant of trimming errors. Trying to soup-up a low aspect ratio, traditional sail, designed to perform best as a reacher by inducing camber may not give you the kind of performance that you're looking for. There is a reason that you don't see windsurfers blasting around these days with fully-battened, camber-induced squaresails. I for one would be pretty astonished if you can wind-up with performance that approaches a modern multihull sail. They aren't made that shape just to look pretty.
Low aspect ratio (not a lot of lift-generating leading edge for the amount of sail area present) is one problem, mast turbulence (which is going to be substantial compared to something like a rotating or wing mast)is another. As far as I know, it just isn't possible to approach the kind of lift to drag ratio of a modern multihull or windsurfer sail with most of the traditional shapes and sail-rigging systems.
I'm not sure what you mean about batten chafe. About 95% of batten chafe problems are directly related to how smooth the ends of the battens are and how well the batten pocket's ends are designed and reinforced to accept them. Wooden battens are usually less prone to chafing than most modern materials, with fiberglass being the worst. It will abrade through almost anything. On a traditional sail a good leather patch reinforcing the forward end of a full batten pocket will usually do the trick. In any case, if the pockets are well made you shouldn't have to worry much about chafe with battens of any material.
04-30-2003, 11:17 PM
Thanks Todd always helful thoughts.
Funny you meantioned windsurfer rigs, that's what I consider the best example of a modern batwing, some are actually marketed under the name BATWING :eek:
I would think getter a gunter to behave like a modern rig wouldn't be to much of a problem :confused:
My mast, though not airfoil shaped, will rotate in it's step. I looked into wingmasts, but on boats this light they become problematic.
Read about CLC's Mbuli (http://www.clcboats.com/pacificproa.php3?cart_id=CREATE)
Wingmast can't be reefed, so the boat is always under power. They had to stake it to the beach when they came in. The latest plans don't use the wingmast.
I am bumping my rig size though, with the gunters the rig will be 20ft high, and will now have over 200sqft of sail, on a 300lb boat :D
That's still a relatively low aspect ratio, but I want to keep the CE low and crank up the power. Much like a sandbagger
and yes I've given thoughts to the low overhanging boom, and long jib pole.
The prototype will be made from dimensional lumber and either clear plastic or (gag) polytarp.
If it doesn't work I'll go with the wingmasts.
As far as chafe I was refering to the square edges, not the ends will will be hinged at the mast. They don't need to rotate around the mast, as the mast rotates, but they need to be able to rotate up when reefed. With the taller rig I may need to cut the number of battens down. With a small displacement craft weight is becoming a factor. Another point for wingmasts I suppose.
I'll post a sketch of the bigger sail plan later.
[ 04-30-2003, 11:27 PM: Message edited by: brian.cunningham ]
05-01-2003, 01:23 AM
Pet peeve: Windsurfer sails are not Bat-wings and neither are nearly all of the small boat and canoe sails currently being marketed as bat-wings. Even companies like Balough Sail Designs and Lost In The Woods Boatworks, both of whom I have a lot of respect for, are guilty of labeling their full-batten, cut-away foot (windsurfer-type shapes) sails Bat-wings.
Somewhere along the line, somebody decided to borrow the term from what traditionally was a very specific type of sail and apply it to their sailboard sail-inspired canoe sails as a marketing tool. Unfortunately, they hadn't done their homework and never understood that the characteristics which define a true bat-wing aren't present on their designs. Other people then borrowed the idea and a whole crop of new sails were cluelessly dubbed bat-wings.
The sails shown in the drawings above are true, traditional bat-wings. They are usually gunters, sliding or folding, and have large roaches supported by the topmast and one or more angled full battens which fan out from a point on the luff close to the heel of the topmast (which by the way, may not always be much of a mast, but more like a big batten). True bat-wings may have a lower batten that is separate and horizontal to support the lower part of the sail, but the big roach is supported by the fan-like system of upper battens. The vast majority of the sails currently being labeled bat-wings are just fully battened sails with parallel battens and big roaches and are no more bat-wings than the main on that Farrier trimaran pictured above.
I see your biggest challenge as being trying to figure out the cut and shape on the sails. Small boat gunters that really set well can be a real bear to design. Much of this is due to the fact that the mast tends to bend a lot and since it's two pieces, often at different angles, often with different diameters and flexibilities, with an overlap where they meet that often has different flex characteristics than either chunk has separately, held together by a halyard that may or may not be stretching with the puffs, combined with the fact that the line of the luff may actually sometimes have a jog in it about halfway up, etc. etc. - you get my drift. I hate making the darned things and have been known to make my customers assemble the spars on the floor, hook up a temporary mainsheet with a scale attached, add various amounts of sheet tension, trace the bend in the tensioned spars on a sheet of paper and send me the tracings before I'll design the sail. Even so, the finished design is still pretty much of a guestimate of what will actually happen out on the water.
Adding a pre-cambered shape to the mix, as you intend to do, adds another major-league layer of complexity and guesswork to the process, so you have your work cut out for you. I would suggest poly-tarp for the test models as it's more stable and will be a better simulation of the type of stability that real sailcloth will have, but I'd work my way around the roach with panels cut square to the leech in those areas. Using one or two big chunks that strike much of the leech off-threadline won't give you accurate information for the eventual conversion to real fabric.
05-01-2003, 10:49 AM
On a true batwing, as I understand it, at least some of the battens (he he) converge:
(Do you suppose that little guy has any problems with chafe? Those lovely, long struts are his finger bones! )
Balogh calls this thing a Batwing, but it just ain't right:
05-01-2003, 07:06 PM
LOL Bruce :D
I couldn't agree more on both you opinions of the windsurfer batwings ( hence the :eek: )
I'm trying to modernize the aerodynamics of the rig w/o taking away the beautiful looks, and functionality. Much like what Nigel Irens did with the lugsail.
I wish I had a nice picture of the 88-class St. Lawrence racing skiffs that were at last years WoodenBoat show. Inspirational!
Here some pics of Yakaboo the boat the originally got me hooked.
If you have time to read it, a book about his adventures are here:
I can see the "bump" your talking about Todd.
I was rather suprized that they used a two inch diameter mast for even the 100sqft! :eek: You right it's more of a batten than a mast. Looks like I need to step up that mast dimension.
Hey wait aren't bats bones hollow!
The bat got it right to begin with! :D
[ 05-01-2003, 07:13 PM: Message edited by: brian.cunningham ]
05-01-2003, 10:18 PM
Yep, your masts will need to be pretty sturdy. You're also subject to the "flagpole principle". Trimarans are quite limited in their ability to heel in a puff and spill wind pressure on the rig. Like a flagpole, the masts have to be strong enough to take the force upright or they'll snap. On a bat-wing, it's often possible to use a topmast that is light enough that it leans to leeward in a puff, absorbing shock and spilling some wind. In your case though, it would add another axis of mast bend to an already very complex sail design problem and I think I'd try to avoid that by using a stiff topmast.
The photo of Yakaboo shows this kind of bend. It also shows a great example of a problem that often happens when you try to rig a jib on an unstayed mast, something that I seem to be getting a lot of recent inquiries about from sailors wishing to increase their sail area. Without shrouds or some sort of backstay to fix the masthead in position, the only things that can keep the jib luff tight are mainsheet tension and the inherent stiffness of the mast.
Yakaboo is either sailing a reach in the photo, or sailing upwind with the sheets eased to avoid being overpowered. In any case, there is very little mainsheet tension pulling the boom in and down, pulling the masthead back and tensioning the jib luff - which is sagging like crazy. This adds a substantial and usually undesirable amount of draft to the sail. This one's shape looks more like a spinnaker than a jib. It's not the kind of shape you want, especially in a blow. Sailing close-hauled, with the main sheeted-in tight, it probably looks fine, but here, or any other time the mainsheet is under low tension or the boom is outboard, the jib isn't contributing much to the boat's performance. In this case, it does contribute something since it's needed for steering (no rudder, the boat is steered by sail trim) but it's certainly not a very good jib shape and is typical of the potential sail shape problems you face when rigging a jib on an unstayed mast.
[ 05-01-2003, 10:20 PM: Message edited by: Todd Bradshaw ]
05-02-2003, 12:58 AM
It is rather like mounting it in concrete ain't it smile.gif Stays it is!
Good thing the outriggers aren't done yet. ;) I need to move the crossbeams so they're behind the masts and not infront. That way the backstays can be attached, just like an iceboat.
The overlap of the topmast and the mast on batwing is 50%, if I decrease it, that would give the "gust factor" you described. I was thinking that effect was a bad thing, but I wasn't thinking about gusts! the only trouble in doing that is the jib becomes smaller moving the CE backward.
How far back do you think I can move the CE? With a multihull the 3 dimentional drag of the outrigger needs to be taken into account. If you look at CLC's proa, it balances w/o a jib at all! The daggerboard is way out on the float. I'll be running assymetric leeboards all the way out on the floats. Three rudders. I might make the outer rudders assymetric as well, pulling them up with the leeboard whenever I tack.
When you raise the aspect ratio of a Batwing too much it starts looking like a chinese junk sail. I can like with that on on mast but not both. If I can let the CE go further back I can leave the mizzen more traditional looking.
thanks again for your thoughts.
05-02-2003, 02:06 AM
I don't know enough specifics about the plan to make any kind of reasonable guess about moving the C.E. My gut tells me that if it was going to balance before and if all the wet parts stay in the same places and the C.E. is moved, the balance will change and probably not for the better. Correction for this usually means dragging the rudder through the water at a less than ideal angle to compensate, which is the kiss of death, speed-wise on a multihull. Why does this little boat need three rudders? My Farrier trimaran seemed to get around quite well with just one.
05-02-2003, 02:16 AM
1) concern about being "locking in irons"
CLC's SailRig is notorious about it. SWIFTWOOD with it's 20ft outriggers will be even more so.
2) if I "fly" the kayak I need a way to steer :D
All three are kickups. I may not run will all three in the water at the same time.
05-02-2003, 09:53 PM
I'll give you credit for one thing B.C. - you are definitely not short on ambition! I like that. The boat's not even finished and you're already flying the main hull. I saw photos of an F-27 flying the main hull once. It puts some incredible strains on the rig and you have to be sure your leeward ama has enough buoyancy to stay on top of the water under that kind of load or really bad things can happen.
Once you start sailing your boat I think you'll find that on a multihull, rudders are not what keeps you out of irons. In fact, they're pretty much what puts you there in the first place. Tacking any multihull seems to be more a matter of having enough speed to start, keeping that speed as long as possible and then trying to get the boat to start accelerating on the new tack at just the right time, but not a second before the right time. The boats aren't all exactly the same and some are definitely harder to tack than others but most respond best to a very gradual turn with just as little rudder action as you can get away with. Too much rudder, creating too sharp a turn just slows the boat down and when you finally get head-to-wind you don't have enough glide left to ease the nose over onto the new tack.
It's a learning process which can sometimes be frustrating at first as you try to find the proper tacking rhythm for your particular boat. Once you figure it out, tacking becomes second nature but it almost always revolves around keeping speed for as long as possible by very delicate use of the rudder.
On your boat, you should also be able to use the sails for help during a tack. As soon as I started up above close-hauled and started turning the rudder I'd sheet in the mizzen hard, letting it help weathervane the boat. I'd bring the main across "naturally" - not trying to force it and I'd leave the jib sheeted in and cleated. As the nose goes through the eye of the wind it will backwind the jib, which will now be on the wrong side, but it will be pushing the bow down onto the new tack. At about the same time, easing the mizzen will stop the weathervane effect and make it easier for the jib to push the bow down. Once the bow is clearly over on the new tack you uncleat the jib and let it cross over. It sounds like you need four hands to manage the tiller and all those sheets, but it's really not too bad. With practice you'll probably get the rhythm down and you can stop backwinding the jib and just tack it normally. The key is still not to scrub off too much speed, especially with the rudder.
If I had a typical trimaran with a single rudder mounted on the stern of the main hull and had to find a place to put a second rudder, the only place on the boat that I would consider putting one would be on the main hull's bow. Ama-mounted rudders would seem to me to be just another source of drag.
05-14-2003, 07:03 PM
I found this picture of a tradtional batwing rigged sailing canoe here.
I may wind up going with a gaff rig.
from the sketches I've been making Bawings really loose thier beauty when changed to a high aspect ratio. Looks more like a dragon fly's wing.
A gaff however looks real nice smile.gif
and I like Wharram's wingsails.
05-15-2003, 12:08 AM
Aren't those short gaffed Wharram sails nice? I really like them too. Going higher aspect ratio is probably a good idea if you really want this thing to boogie. Have you seen Gary Dierking's site? He's got some interesting boats and ideas.
I helped him a bit when he was trying to figure out the best way to build a Dacron version of this high-aspect poly-tarp prototype.
I haven't talked to him in a while to check up on his progress with it, but it looks very interesting and talk about aspect ratio!
05-15-2003, 12:18 AM
Well I can honestly say I've never seen that before.
Nice thing about the gaff rig is that it's a well know design, everything from cargo schooners to high speed ice boats use them. So I should be able to get it tuned out a lot easier. Though I loose the ability to telescope the mast. One the other hand all the "pieces" are 20ft long now, since I'm also widening the overall beam to 20ft. Ted Warren said I should run it "square" for best performance.
Powered by vBulletin® Version 4.2.3 Copyright © 2015 vBulletin Solutions, Inc. All rights reserved.