Balanced Lugsail, Angle of Mast

[Ron Hotchin]

I,m looking at changing a sprit rig to an unstayed balanced lugsail, and wondering if there is an optimum angle of rake for the mast. It seems to me a perpendicular mast would reduce twisting between the foot and the head, but some amount of rake would help "pre-load" the mast. Any advice out there?

[Wooden Boat Fittings]

Ron, the main thing to consider will be how far the CE moves, and in which direction. You will need to draw up before-and-after sailplans.

It's impossible to generalise because sail shapes can vary so much, but I suspect the CE will move forward a bit. So if you've currently got a lot of weather helm, you may find no change at all is needed. But at the other end of the scale, you may find that you need to restep the mast.

Once you've done what you can with the theory, you'll probably find that you need to experiment a bit on the vessel herself. Which leads me to ask -- how big a boat is she, what sort of mast is it, and how is it stepped?

Mike

[Todd Bradshaw]

Optimum angle of rake is most likely zero. You don't need to "pre-load" the mast on a balanced lug and I don't think you're apt to gain anything by trying to do so. As Mike pointed out, it might be a good idea to figure out the C.E. for both systems to be sure that your changes don't throw off the helm balance.

[Ron Hotchin]

The boat is a Catbird 16, and as designed by Karl Sambaugh it's a sprit rigged ketch. I checked with Karl, and he believes changing to a balanced lug is feasible. I want to do it so I can unstep the masts while afloat to get under a low bridge; too rocky to land, and the sprit rig is awkward. I've done the calculations on the C.E. The mizzen mast can remain as located, but the main has to be moved. Since I haven't started building yet, the plans can be changed, but I'm hoping those familiar with balanced lugs can let me know the implications of any mast angle. I appreciate the help.

[Wooden Boat Fittings]

There aren't any particular implications that I'm aware of, Ron. As Todd said, it should not need to be raked at all (and on most boats would not be.)

A boat this size would normally have mast partners consisting of a thwart set high up under the gunwale with a hole through which you lower (or into which you clip) the mast, and a tenon on the kelson for the heel to step into. I take it your plans aren't radically different, although I'm not familiar with this particular vessel.

However, since she's still to be built, a little ingenuity would allow you to make an adjustable mast-step so you could change the rake a small amount by experimentation if necessary.

[Todd Bradshaw]

I love a good rig design challenge, so here's the scoop. I looked up the profile drawing and sailplan. First of all, they aren't spritsails, they're sprit-boom sails. This makes the re-design a bit easier since we aren't just shifting a 4-sided sail forward to change it from a real spritsail to a balanced lug and thus moving the mainsail C.E. forward and potentially screwing up the balance.

I had to work from a fairly small drawing, measuring in millimeters and multiplying to get inches and feet - so my figures aren't exact, but they are pretty close. By the way, the sail area figures in the drawing are placed on the sails as if they also represent the position of the individual sails C.E.'s. They don't, so I relocated the real centers and generated the real combined C.E.

My primary criteria for the balanced lug main were as follows:
- The fore-and-aft position of the mainsail C.E. and it's area had to stay the same.
- The mainmast would be plumb and stay in the same location as on the original plan.
- The height off the deck of the bottom of the sail at the mast would stay the same.
- Foot length and angle to the horizon would stay pretty close.
- The yard would be peaked-up as much as possible for pointing, yet be short enough that it doesn't hit the mizzen mast when furling the mainsail (higher peaks take longer yards).
- Some vertical change in the boat's total C.E. (main and mizzen combined) could happen, but I wanted the fore and aft position to stay very close to the original (like a couple inches, max.) - close enough that the helm balance probably wouldn't change enough to be noticed.

This is what I came-up with

http://albums.photopoint.com/j/View?u=1302883&a=13887415&p=56499231

Basically, it worked pretty well. The Combined C.E. is very close to the original one (fore-and-aft) even though both it and the mainsail's C.E. are a bit lower than the original ones. The boat might heel a bit less. The shorter rig might also lose a little bit of performance in light air, but that's to be expected with this kind of change.

The strangest thing seems to be that now, the sprit-boom mizzen is taller than the mainsail (it's a schooner, it just doesn't know it). I imagine that it's possible to "squeeze" the design of the main, making it a little taller and thinner or modify the mizzen's shape to look more like part of the plan and less like a Laser sailing by in the background. Something a bit more traditional might go better with the balanced lug up front.

[Wooden Boat Fittings]

Good work, Todd.

There you go, Ron -- now aren't you glad you got up this morning?

[Ron Hotchin]

Todd, thanks for the input. Perhaps one communication problem, however. I intend to change both sails to balanced lugsails. Also, it's easier to move the location of the main mast if necessary, as the mizzen is stepped through a thwart that also supports the centerboard case. The main is through a mast partner incorporated into the deck, which I can adjust. I also came up with a lowered CE with the lugsails and thought I might increase the total sail area from 110 sq ft to about 115 sq ft to help the light air performance a bit. Do you feel like chewing on this problem a bit? It could help me a lot. Thanks again.

[Todd Bradshaw]

Ron,
From a cosmetic standpoint, that's probably a good move. The trick is going to be creating enough clearance between the tail of the main boom and the front of the mizzen. It should be possible to similarly convert the mizzen to a slightly scaled down version of the main without needing to move it's step and without changing the rig balance - but now it's luff will be forward of the mizzen mast and we may need to make both sails taller and skinnier to get enough clearance between them.

I'm pretty well convinced that both masts can still be stepped in their original spots. It will just take some figuring. Let me kick it around and see what comes-up. The other thing that would be nice about not moving the masts is that just in case you ever decided you also wanted to try the original twin sprit-boom rig, the masts would drop right in place. As rigs, masts and sails go, they would be fairly reasonable to build in terms of cost, time, etc. and you could have two interchangable rigs.

[Ron Hotchin]

Todd,
Thanks for the trouble you're taking on this. If I can help with any info from the plans such as the present overall C.E. or anything else, just let me know either on the forum or by e-mail.
Ron

[Todd Bradshaw]

For those who enjoy doodling on boat plans, or who simply have "enquiring minds that want to know", here is the original sailplan
http://albums.photopoint.com/j/View?u=1302883&a=13887415&p=56540942

In order to get two balanced lugs to clear each other, fit into the same mast steps, have similar total area and maintain the rig to hull balance, I went with two fairly tall sails with smaller heads. The portion sticking out in front of the masts had to be pretty narrow and the mizzen mast is raked slightly as in the original plan. To get them to balance, the mainsail area had to be decreased a bit and the mizzen area increased.

The result yielded a combined Center of Effort that is just under 5" lower than the original and 5/16" farther forward, which should be well within tolerances for the C.E vs. C.L.P equation and a balanced helm. The new sailplan looks like this:

http://albums.photopoint.com/j/View?u=1302883&a=13887415&p=56537423

and once it's added to the hull, it looks something like this:

http://albums.photopoint.com/j/View?u=1302883&a=13887415&p=56540943

My greatest concern would be luff tension. Proportionally, these are pretty long luffs for balanced lugs and it's important to get them tight through a combination of halyard tension vs. downhaul tension and sheeting tension on the boom. The sail could also be built loose-footed, which might give more draft adjustment.

Whether the lug-rigged boat would sail as well as, worse than or better than it would with the original rig - I don't know. The twin sprit-boom gets a lot of performance out of a very clean, simple set-up and has to be admired for that. Another interesting balanced lugsail possibility might be one with fully-battened Chinese-style lugsails.

[This message has been edited by Todd Bradshaw (edited 11-19-2001).]

[Ron Hotchin]

Todd,
What a great job! This was my first chance to check today, and I was very pleasantly surprised to see what you've done. From your post time you must have been working on this halfway through the night. There was a string recently about where this forum is going,its relevance,etc. For me, this is exactly it; a place to get help from all the ideas and experience out there, and occasionally perhaps help someone else. I was fortunate to connect with someone with the expertise and interest to solve the problem, and I want to thank you for that. Once the boat is reality I'll post a picture here so you can compare it to your drawings! Thanks again,
Ron

[Todd Bradshaw]

Glad I could help. I only sleep 4-5 hours a night, so I'm up late. Any more than that kills my back and I wake up really groggy. Late fall is also really slow for business so I have a lot of time to work on plans, but no money to do anything with them.

Just for fun, I re-rigged the boat from a different perspective. Chinese anyone?

http://albums.photopoint.com/j/View?u=1302883&a=13888485&p=56563213

It still baffles me how a flat sail with fairly stiff battens (to make sure it stays pretty flat) can move a boat, but many of the sailors who have them swear by them. The look is different to be sure. Most people either like it or hate it.

For this one, the mast steps are the same, as is the fore and aft balance. The new C.E. is 10" lower than the sprit-boom and I didn't rake the mizzen mast, though it could be done without actually moving the sail itself. I increased the area about 10 sq. ft. because it's a low rig and they are very easy to reef. Usually there is a parrel for the mast on every batten. It makes a built-in lazy-jack-type sytem which helps control the sail during raising, lowering, reefing, etc.

I set each sail up with a normal mainsheet, rather than junk-style with small mini-sheets going to the aft end of each batten. It could be done, but involves a lot of strings. I've never tried one of these "bridle-style" systems, but they are supposed to give excellent control of sail twist. Either way, it would be a very distinctive looking little boat.

T.E.B.

[Ron Hotchin]

Now that junk rig really is different, but I like it a lot. It seems to offer some real advantages, particularly with the possibility of the increased rig for light air combined with the relatively easy reefing capability. Is there anything that is a significant inherent performance disadvantage with the junk rig? I imagine it would also be considerably more expensive to produce these types of sails, wouldn't it?

[Todd Bradshaw]

The Chinese-style lug rig probably won't perform as well upwind as the other one since it doesn't really have the type of camber that generates large amounts of lift. On the other hand, there have been plenty of cruising boats that have sailed all over the world with similar rigs and this is a pretty light (350 lb.) boat that shouldn't need tons of power to get it moving.

Like any rig, there seem to be both advantages and disadvantages. In this case, it's biggest advantage is that the sail handling tasks are so simple. In contrast, the regular, Western-style lug will likely point higher and may generate more boat speed on some points of sail. How much is hard to say. On a beam reach, it wouldn't surprise me if the Chinese lug with it's big roaches was faster.

Construction costs are also give-and-take. The design and sail shaping is much easier on the Chinese version as the sails really are cut flat. The trim-out is a bit more complex, having to attach the battens and protect the sail from batten chafe but, for example, it is simpler than building a full-battened catamaran sail with batten pockets end caps, tapered battens, etc.

Battens here would be thin, varnished strips of wood, laced to both sides through small grommets and sandwiching the sail. The visible wooden battens give the sail a really elegant "skeletal" look. Combined with wooden spars, cream or Tanbark colored Dacron and multiple little strings of parrel beads the rig would be visually eye-popping, even if it's not the fastest boat on the lake. I'm terrible at "off-the-cuff" pricing (at least I usually wind-up screwing myself, not the client) but I'd imagine that the Chinese lug might be 20%-25% more than the Western version from most sailmakers.

[Ron Hotchin]

Todd,
Thanks again. I really like the junk rig, but I'll probably end up with the balanced lug because of the expected better upwind performance. I figure downwind and reaches are limited by hull speed anyway. Perhaps if I want to enter a Chinese regatta some day, the junk rig could turn up as a set of fun and inexpensive tarp and duct tape sails! Your replies have generated a whole bunch of "inquiring minds need to know" design questions that I hope I can pose to you. Are there any recognized "ideal" proportions for the balanced lug or are they basically made to fit the space and CE limitations? The ratios on the first sail are very different from those on the second set. Would the second set, with the higher aspect ratio be expected to perform better than a set of shorter, wider sails? Should the luff, as the leading edge ideally be plumb, or does it matter? Finally (for now at least)how are the balance/pivot points of the yard and boom determined where they meet the mast? Cheers, Ron

[Tom Dugan]

Ron,

I'll be the first to say that I'm enjoying this exchange immensely. But since Todd isn't likely to toot his own horn, I should remind you that there is a book that goes over a lot of what you're asking.

http://www.woodenboat.com/325110.jpg

Author? Todd Bradshaw.

I've got it. You should get a copy, too.

Now please! By all means, carry on.

-T

[Ron Hotchin]

Well I'll be darned! I'm familiar with the cover, I guess because it's so distinctive, but I must admit I hadn't made the connection. Thanks for the heads up. I believe I will get a copy (I'll let SHMBO know she's giving it to me as a birthday present!!)

[Greg H]

Uh Todd, since you've got time on your hands.... http://media5.hypernet.com/~dick/ubb/smile.gif
I've been trying to work out a ballanced lug yawl rig for Oughtreds Whilly boat.... http://media5.hypernet.com/~dick/ubb/smile.gif
Greg H.

[Todd Bradshaw]

There may be a short time-out. Not because I'm busy, but because my cable company's Internet provider is going broke and they are switching. I just spent two hours on the phone with their tech guys trying to get their conversion program to work with no success. I had to patch the undeleted parts of the old stuff back together to get it to work at all and now everything is really messed-up.

Naturally, the process will also screw-up my e-mail as I have to get a new address for it as well. I've already gone from Kevlar radials back to sewn rings and roped edges, now I'll probably have to go back to using two dixie-cups and a string for communication as well.

T.E.B.

[Todd Bradshaw]

It's Aliiiiive! At least for the moment.
Ron,
The first Western lug was basically one that I had lying around in the computer that was close enough in terms of C.E. location to be tweeked until it would line-up properly with the plan. The second one (the pair) was designed specifically to fit the boat and the Chinese sails were a combination made by heavily modifying the plan for a sail that just happened to be a very close starting point for the pair.

For the tall, Western sails, not moving the masts and projecting sail area in front of the mizzen meant that it would need to be a taller, skinnier rig to balance properly and for the sails to clear each other. The fixed location of the masts and C.L.P. also dictated that the sails be closer to each other in size. Since the leading edge of a sail generates the best lift (hence the reason for modern, high-aspect sailplans) I steepened the peak angle to get more leading edge and thinned out the top a bit to keep the upper part of the sails somewhat closer to the original sprit-booms in terms of area aloft and heeling power.

I'm sure there is a point at which a lugsail can be either too tall and skinny or too short and fat to be particularly efficient, but I'm not sure anybody has ever studied it enough to put specific guidelines in writing. Since we haven't gone to extremes, I think we're safe in this case.

Luffs on balanced lugsails are traditionally parallel to the mast, though some variation is allowed. It helps give them their semi-self-vanging characteristics. It can also make the rig more stable dead-downwind by putting sail area both to port and starboard of the mast, rather than all of it hanging off one side as on a Bermuda mainsail. In this case it's not a great amount of area because of the tall, skinny rig, but there is still some.

The yard/boom vs. mast placements were done to get the C.E.'s and more importantly, the Combined C.E. to end-up where it needed to be without having to re-design the hull. Remember, this whole C.E. vs. C.L.P. relationship is a design tool, not a phsical law. Other than high-tech computer design and testing, it's about the most accurate tool we have for developing a sailplan that works. In real life with different wind and water conditions, different amounts of heel, different crew weights, points of sail, etc. the real C.E. and C.L.P. are constantly changing. This is an average that has proven to be pretty reliable.

Since we don't have the C.L.P. marked on the plan we have to assume that the designer figured in the right amount of lead (C.E. forward of C.L.P.) and we maintain it by not monkeying around much at all with the fore-and-aft position of the combined C.E. We also don't want our new C.E. higher than the designer's original one making the boat less stable, increasing heel angles, etc. In some conditions, the boat might sail better with the halyards tied slightly forward or aft of normal and the sails tilted a bit, moving the C.E.'s and changing the balance.

Since you also have a twin-sailed rig, a lot can be done with sail trim to affect the way the boat handles. A yawl, for example gets very little power out of a dinky mizzen. It's too small and is generally very flat creating little lift, but it is quite handy for adjusting helm balance. I recently built a pair of balanced lugs (ketch rig) for a guy in North Carolina with a sailing canoe. He tried it out last weekend (before building the rudder) and was surprised at how well he could steer the boat by just trimming or easing the mizzen.

Another interesting thing which you will see the first time you raise a lugsail is that unlike most other types of sails, it doesn't naturally want to hang at the angle that it is designed to be at. It wants to pivot at the halyard attachment point, dropping the tails of the boom and yard.

On a balanced lug, the main thing that keeps it upright is the parrel or boom jaw pressing on the back of the mast. On a standing lug, it's the force generated by the downhaul attaching the tack corner to the mast, jaws or gooseneck. These things combined with the weight and force created by mainsheet tension and all that yard and sail hanging behind the mast is, in turn, what keeps the luff tight.

The first lugsail that I ever built was a small standing lug for a Peapod. When I took it out and hung it up in the yard I was amazed at how much downhaul tension it took to peak it up. Even on small lugsails, I rope the luff, double the luff tape or hide a piece of webbing under the luff tape to reinforce the edge because I know it's going to be under a lot of strain. You'll see what I mean when you launch your boat.

Oh well, enough rambling. Lets see...Whilly Boat? I'll see if I can find a plan.

[Ron Hotchin]

Todd,
Thanks again for the info, it's helping me a lot. I've decided Im going with the balanced lug. I'm also going to build the boat without the cuddy and put in a second thwart/mast partner so I can sail with just the main if I want a particularly lazy sail. This also will give a whole bunch of options for reefing, especially with a reefing point on each sail. Now if I can just convince my wife that I need to build the boat before I build a new buffet hutch, coffee table, and bedroom furniture for her http://media5.hypernet.com/~dick/ubb/smile.gif