Balance Lug Design Ideas.

Discussion in 'Sailboats' started by LP, Jul 20, 2013.

  1. LP
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    LP Flying Boatman

    I recently ran across this thread.

    http://www.boatdesign.net/forums/sailboats/junk-lateen-yawl-22225.html

    It struck me more as a balance lug rig with full battens rather than a "junk lateen" as it is presented. The key component of interest to me in the design was the offset of the lug so that it is separated from the mast and the possibility for a clean sail on a balance lug. The main problem I see with a cantilevered support at the top of a mast is the couple that is created at the weakest portion of the mast.

    I've drawn something up that addresses these issues and I'm presenting them here for some member feedback. The biggest underlying question is whether the unconventional design components are going to be justified by performance returns or other benefits.


    In order to have an offset lug, the couple moment at the top of the mast needs to be negated and I think that I have done this by incorporating a set of spreaders at the top of the mast. One side separates the lug from the mast and the other is used to balance the load forces of the tensioned sail. The loads induced by the sails, spars and downhaul are carried back to the hull by means of a head strap and single shroud on the opposite side of the mast. I have essentially taken a free standing mast and converted it to a stayed mast and utilized the sail as part of the staying mechanism. The single shroud is not loaded while the sail is stowed and only tensions in response to the hoisted and tensioned sail.

    The possible benefits of the rig are better performance due to a cleaner sail shape, especially when combined with full length battens. A possible lighter rig due to smaller mast since it is stayed laterally. Less windage due to a more aerodynamic rig.

    To the rig's detriment, the reduction in mast width may be limited by the fact that the rig becomes unstayed when the sail is lowered. This impacts the windage aspect and we also have the increased windage due to the added shroud. The net performance enhancement could be negligible or negative.

    I think that the critical element to a successful enhancement of this rig type would be whether or not there is a substantial reduction in mast width and the accompanying weight and windage reductions. There is nothing so simple as an unstayed mast and this idea may end up being a bunch of mental gymnastics. I suspect that unless I can determine a way to keep the mast stayed while the sail I anywhere, but hoisted and tensioned, I will still need the full dimensions of an unstayed mast. The gain in performance on one tack vs. the additional rig drag on both tacks could very well be counter-productive. A second shroud would be one solution, but I feel that the lug is starting the get too encumbered in it's own rig.

    I'll leave it at this for now. Feedback and ideas are appreciated.
     

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    Last edited: Jul 21, 2013
  2. Timothy
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    Timothy Senior Member

    I thought about running the halyard through the mast head and down to a block on a chainplate to windward but I think yours is a much better idea.
     
  3. LP
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    LP Flying Boatman

    I had actually thought about that, too. It would have been great to get double duty out of the halyard, but the problem that I saw was that it would need to be fixed to provide any staying action and it would need to run free to act as a halyard. And again, the mast would be unstayed if the sail was down.

    My current thoughts are towards a spectra type shroud on the sail side that only comes into play when the sail is released. I'm thinking it could be loosely sheeted(shrouded?:D) while the sail is lowered and when the sail is hoisted and the down haul tensioned, it would either fall slack and lay against the sail or be released enough not to interfere with the sail or the lug. It would not need to be a strong line as it only comes into play when the sail is down, but caution says to make it strong and only slack it if it is interfering with the lug.
     
  4. sharpii2
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    sharpii2 Senior Member

    I've thought of another way to offset the Boom and Yard from the mast.

    The offset strut would be attached to a hard sleeve, roughly double its length, which would travel up the mast.

    The two would form a rigid 'T' shape with the strut forming the stem of the 'T'. This would be a rigid attachment, so the strut could not flop up or down.

    The other end of the strut would have to rigidly attach to the yard, so the yard would be free to pivot up and down, but not side to side, in relation to the strut.

    The Boom would have a similar arrangement.

    There isn't much profit in slimming down the mast, as the rig should be short for its sail area and you could streamline it with a collapsible sock ( you may have to pay Mr. Hoyt a license fee for the sock, as he has no doubt patented the idea, if at all possible).

    This set up would have all the virtues of Mr. Hoyt's similar design, but not the major vice, which is the yard stays at the top of the mast, when the sail is furled or reefed.

    The one vice this proposal would have is the Yard and Boom would not be able to be stacked together, as the sleeves would hold them apart.

    The solution to the problem would be to abandon the 'T' connection in favor of an 'L' connection, with the Yard's sleeve pointing up and Boom's sleeve pointing down.
     
  5. LP
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    LP Flying Boatman

    It took me a moment to grasp your T concept. It makes a lot of sense and certainly distances the sail from the mast on all points. I think I would want the sleeves removable without unstepping the mast. How would you plan the downhaul; a strop around the base of the mast that can swing with the T or L fitting?

    It might be verging on gadgety as is mine with the addition of another shroud. If my mast didn't have to be up in the eyes of the boat, It would be tempting stay it in three direction, resize the mast to a stayed mast, fly a jib off of the forestay and bowsprit and position the boom so the forward end cleared the mast entirely.

    One of the features of the balance lug that I want to take full advantage of is the fact that it needs no mast attachment. To get proper sail shape with the rig, it take a lot of down haul tension. So much so that the entire sail is strung between the halyard and the downhaul (and of course the sheet). I think that there is great potential in have almost half of the luff free of any wind blockage. I would also like to add aerodynamics to the lug, but I'm still studying the rig and I'm not sure about how the lug should flex to get it to de-power during gusts. I'm thinking that it might need to flex in the lateral and vertical and that will limit spar shape to balanced sections.
     
  6. LP
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    LP Flying Boatman

    So here is a dual shroud version along side the original and then there is an unstayed version thrown in that really makes the stayed versions look a whole lot more fiddly. I lengthened a spreader on the dual shroud version to gain some clearance on the lug and routed a halyard strop though the spreader. It might be just as functional to run the spectra shroud to an attachment on the head strap.
     

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  7. sharpii2
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    sharpii2 Senior Member

    Precisely.
     
  8. sharpii2
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    sharpii2 Senior Member

    STAND OFF BALANCED LUG

    LP.

    You don’t need a shroud on your halyard side, as the windward side only has tension on it when the sail is hoisted. Other than that, the mast as shown, should best be left free standing. Rigs with yards don’t like stayed masts very much, as there is so much opportunity to foul. This is probably why the gaff was invented. To keep the would be yard tightly secured to the mast at its butt end.

    I have had other ideas for a stand off BL over the years.

    One was to have parallel masts with a cross piece joining them at the top.
    The Yard would be suspended from the center of this cross piece.

    The disadvantage is, when the sail is reefed, there is so much line between the cross piece and the Yard, that the Yard will tend to creep over to the lee mast.

    One remedy for this is to have the bitter end of the halyard attach to the top of one of the masts. Then have the halyard reeve through a block on top of the Yard then over a sheave at the top of the other mast, then down.

    This will alleviate the problem somewhat, but will call for a halyard that is twice as long (which you may need, anyway, for sufficient mechanical advantage).

    What would make the most convincing cure would be to have a sliding cross piece, beneath the fixed one, which the yard would be attached to. This would insure that the Yard stays centered between the masts.

    But to make this rig, or even the one you are proposing, or the stand off strut one I mentioned earlier, you have to go to a lot of trouble.

    The simplest thing to do would be to add a chafing patch to the sail, that is a different color, and easily removable, when it wears out. It can be made of a material that is quite chafe resistant, as it has no other function.

    Another simpler solution is to split the sail and have the aft portion attach to the mast with lacing or hoops. I have thought of a way of doing it, that I think is so fiendishly clever, (probably not) that I’m thinking of trying to patent it.

    This solution also has its problems. Such as, how do you reef the free flying forward part of the sail? It can be done, but its like reefing two sails, not just one. And now the sail must be attached to the mast, as well as the Yard and Boom.

    BTW, forget about having the entire rig free of the mast, except for the halyard and down haul.
    This may well work on very small boats, such as canoes and pram dinghies, where the crew is large enough, in proportion to the sail, to man handle the spars. Imagine trying to reef a rig like that with 1,000 sf of sail.

    The Yard, at least, is going to need a parallel, to keep it reasonably close to the mast, as it comes down.

    Phil Bolger used to think of the BL as an inshore rig. Its Dipping Lug cousin is the one he thought of as a blue water one.
     
  9. LP
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    LP Flying Boatman

    sharpii,

    Many good points. I agree that the sail side shroud is redundant on the sail side. My concern is if the mast is dimensioned to be stayed and the sail is not hoisted. If memory serves me correctly, a mast can be subjected higher loads in this state than when under a full press of sail, especially in a sea state. It would become static when the sail is hoisted, though it would still present fouling potential.

    I think that the only way this rig has any potential is if it is stayed and mast sizing is reduced accordingly so that weight aloft and windage is reduced. Otherwise, the rig is getting complicated (vs. a standard balance lug) introducing added windage for questionable gains.

    I've considered the dual mast idea too, but couldn't convince myself that the mast pair could be equal to or less than the weight of a single unstayed mast. With a proper downhaul, I think that sail drift to leeward when reefed may only be a minor concern. I'm assuming an A-frame type mast where the masts diverge as they approach the deck.
     
  10. sharpii2
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    sharpii2 Senior Member

    That wasn't my original idea, but it may even work better.

    As the Yard gets lower, the lee mast gets further away.

    Just as you suspect this added complexity will almost certainly increase the weight.

    With my parallel mast idea, I was considering a very short hoist/Yard length ratio of less than 1.0.

    If the mast is half as tall, it can be twice as heavy and have the same VCG.

    So, weight of the mast system took a secondary consideration.

    Every one of these schemes, except perhaps, the stand off strut one, suffers Yard control problems, as the sail is being lowered for reefing or furling. It well tend to kite off to leeward, and may move forward as well. The bigger the Yard, the bigger the problem.

    The parallel mast system (dead vertical and joined with a crosspiece on top, or an 'A' frame) at least always has a mast to the lee of the yard to keep it from kiting off the boat.

    One problem that I failed to mention with the stand off strut scheme is the Center of Area (CA) of the sail will move forward on one tack and aft on the other. This may not be that big a deal, but it's something to consider (especially when calculating the best strut lengths).
     
  11. LP
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    LP Flying Boatman

    I think that I'll let the split mast (?) go by the way side. I just ran across this thread.

    http://www.boatdesign.net/forums/boat-design/frame-masts-47703.html

    I've not read all of the links, yet, but I think it is fairly conclusive that a single mast is more a is more effective than twin masts. That being said, the performance advantage came from the sail being attached to the mast and effecting the airflow around the mast. This is not the case with a balance lug and so a split mast arrangement may still be an effective option for the balance lug. On the pro side of a split mast is the ability to place the mast(s) anywhere along the length of the boat and still keep a clear cabin. My current rig plan is heavily driven by this limitation.

    Here is a split-mast rig with a distinctive heritage. I'm tempted to spend the few dollars to study the rig.

    http://www.dngoodchild.com/divide_for_sail_boats.htm

    You'll have to scroll down to Sailski under multi-hulls. #5666. I think we will have to call this one a lateen.
     
  12. sharpii2
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    sharpii2 Senior Member

    I think I have seen several incarnations of this idea: Sling a lateen yard under the apex of an 'A' frame mast. This usually works when the boat is a multihull, as it is quite wide for its weight.

    I don't think really tall split masts are worth the trouble, due to weight and windage issues. But short to moderately tall ones may well be.

    I envision a BL which has just enough luff for two even area reef points, so the first reef point reduces the SA by 1/3rd, the 2nd one by another 3rd, leaving just a small boom lateen standing, for the final 3rd.

    This would require a hoist to Yard length ratio of about 1.00, plus, of course, deck clearance. The mast should still be quite short for the SA carried. The Yard would have to have close to a 1:1 rise/run pitch, or close to it to get adequate area. Whether it is an 'A' frame, or it has a cross piece, it could be easily be made so it could be pivoted down to the deck with almost no fear of mishap, as it will only pivot fore and aft, not side to side. It could be held up with just a pair of shrouds on each side. These shrouds would not have to go all the way to the top.

    The 'A' frame version would have to be taller than the cross piece one, so there would be enough room for the Yard to pivot. Even so, it would still probably be lighter, as it wouldn't need corner gussets like the cross piece version would.
     
    Last edited: Jul 26, 2013
  13. TeddyDiver
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    TeddyDiver Gollywobbler

    Just MHO but it would be KISS to have the lug spars rigged traditionally and have the sail 'loose footed' in both ends..
    BR Teddy
     
  14. sharpii2
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    sharpii2 Senior Member

    I think that would be a traditional 'dipping lug' (see attachment).

    A good idea. they were common on both sides of the English Channel, back in the days of sail.

    They work best when you always have the yard to the lee of the mast.

    This means you have to move it there during each tack.

    There are various ways of doing this that make it far easier to do than it sounds. Phil Bolger came up with a scheme where a lifting line attached to the aft end of the Yard to raise the aft end, so the front end could be tucked behind the mast. The Tack of the sail could then be hauled around to the other side, behind the mast, much the same way the Clew of a jib is hauled around in front of the mast.

    The whole operation could conceivably be done by just one crew.

    Boats that carried a Dipping Lug tended to be narrow for their weight (but not necessarily heavy for their length) so they would not lose way while the sail was being moved to the other side of the mast.

    The system LP and I are discussing could work on wider boats that are light for their beam.
     

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  15. LP
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    LP Flying Boatman

    I like KISS and I understand your concerns Teddy. I think it's great that we have such a sounding board here at BD to explore possibilities. After these explorations, I am leaning towards the traditional unstayed rig for my main mast. My mizzen, jigger or whatever is offset to accommodate my tiller steering. This makes it a prime candidate for utilizing an offset stayed version of the rig to bring he sail back towards centerline. The mizzen will make a nice test bed for the rig design and I'll have traditional to make comparisons to. At least as far as ease of use and set-up are concerned. Should mizzen be a problem child, I'll have to build an unstayed stick and refit.

    The balance lug is such a simple sail and it has so many positives to it's use, the temptation remove the "bad tack" is very strong.

    Improving a traditional rig is not an easy task. I think that most traditional rigs exist because they worked and most likely worked well. Maybe, one of us will get lucky and be successful in updating an old rig.
     
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