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Thread: Changing from laced to loose foot mainsail?

  1. #1
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    Default Changing from laced to loose foot mainsail?

    As I ponder the "next boat" I find I'm drawn to the Atkins/Williams era designs. After 4 glued-lap boats the serial builder in me wants to rivet cedar planks to steamed oak frames but I also want to take advantage of modern technological advances where it seems prudent. As in: We've got good adhesives today, why not laminate the stem and floors to shape instead of hewing great chunks of wood and bolting them together?

    But this is a question about sails and booms. "Back in the day" it appears they almost always attached the foot of the main to the boom, as far as I can tell this had a lot to do with minimizing the stretch of the natural fiber sailcloth they had available. In modern times, with highly stable sailcloth we can take advantage of that stability, leave the foot loose and develop a more efficient aerodynamic shape. Or at least that's what I've gathered from reading things on the internet and my library of boat-related books.

    1)Is there something to be gained by releasing the foot from bondage? It would appear so, but the question of how much is worth asking.

    2)What changes, if any would need to be made to the scantlings of the boom? Go bigger, smaller or stay the same? Either style has a lot of compression as the tack and clew are locked in a tug-of-war. Laced foot would seem to add a "sideways" pull as the sail is pushed into a curve by the wind that isn't there if the foot is loose. I think mid-boom sheeting would have a similar effect but most of the designs I've been looking at sheet from very close to or at the outboard end of the boom. There is a line of thought that you want a heavy boom on a gaffer to keep it from lifting when off the wind. That makes a certain amount of sense, but you wouldn't want to take it too far either.

    Building a carvel planked boat is anachronistic enough, I'm not building a 'round the buoys racer here but I have to build a boom and sails anyway, why leave X% performance on the table?
    Steve

    If you would have a good boat, be a good guy when you build her - honest, careful, patient, strong.
    H.A. Calahan

  2. #2
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    Default Re: Changing from laced to loose foot mainsail?

    Not all old gaffers had a laced foot on their sails
    Plate 30.jpg
    It really is quite difficult to build an ugly wooden boat.

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  3. #3
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    Default Re: Changing from laced to loose foot mainsail?

    I may well be quite wrong here, but I'm certain others will come along and correct me. Regarding the boom scantlings it depends largely on your sheeting system. If you're sheeting to the end of the boom, you probably won't need to change anything. If you're sheeting to the center, the sail lacing/slides are not supporting any of the sheet loads so you'll want to increase them somewhat. Regarding the potential sail shape improvements of laced vs loosefoot I've always been a proponent of loosefoot for shape. It allows a bit of foot roach and a broader range of draft control. I did have a main with a "shelf" foot...a lighter weight flap built along the foot that would keep it attached, meet a one-design requirement, allow easier control of the sail on dropping and was great for funneling raincatch right down my collar.

  4. #4
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    Default Re: Changing from laced to loose foot mainsail?

    That was more or less what I was thinking too.
    Steve

    If you would have a good boat, be a good guy when you build her - honest, careful, patient, strong.
    H.A. Calahan

  5. #5
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    Default

    I once snapped in half a perfectly beautiful varnished western red cedar boom (:-0) by moving the sheeting from end-boom to mid-boom on a small (24') keeler.

    I'd previously unlaced the foot - that worked just fine for quite some time with end sheeting. But moving to mid-boom sheeting with a loose footed sail (alas, on reflection only) was clearly going to bend/break the boom sooner or later.

    Loose foot is best on dinghies for racing because the outhaul is so easily managed. On bigger keel boats, though, the benefit for sail shape will still be there but be harder and slower to achieve - and if performance is not the point then maybe it might not worth the extra gear.


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  6. #6
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    Default Re: Changing from laced to loose foot mainsail?

    Lots of old rigs had loose footed sails. Boom hardware and the sail have to be beefed up to take care of increased loads which are no longer distributed along the boom. And if you want to go with midboom sheeting you will need to beef the boom up as others have pointed out. I'm sure that there is some math out there which would give you an idea of what you would need to do to prevent breakage. I'm imaging a double taper with the biggest diameter at the sheeting point. My stern steerer gaffer iceboat had mid boom sheeting with a three point bridle to distribute the loads. It was a laced on sail but that isn't what made a difference. Boom was alarmingly light for what I did to it. I also suspect that with point loading on the boom the boom might want to bend more and would need some beefing.
    Ben Fuller
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  7. #7
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    Default Re: Changing from laced to loose foot mainsail?

    Some of the literature has it that a loose-footed sail had the advantage of being "brailed" up (haul the clew up to the gaff throat) to spill the wind when necessary, but this more appropriate in a completely boomless sail. My mizzen is loose footed to a boom and it is easier to get a reef tie around it than if i was dealing with it laced to the boom. Beyond those points I got nothing.

    Ken

  8. #8
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    Default Re: Changing from laced to loose foot mainsail?

    It much depends on the aspect ratio of the main. Modern high aspect ratio sails are much easier to loose foot than older ones. It will somehow change little bit the tension in the sail itself, so it needs to be considered if it is worth to do.

    And as was said the boom strength. If you got loose foot and sheeting on the same place as the clew, than the boom working much more like spinnaker pole (the only force it needs to withstand is the longitunidal pressure).
    If the sheeting is in the middle, than you will need to count with a lot of bending force. And for low aspect ratio mains it means long boom and also higher bending force.

    If the clew is not directly at the end of boom, you will need another rope attached to the clew to have it slide on the boom. Otherwise you would be overtensioning the main.
    This way you can much more precisely tune the sail camber (which is far less possible without loose foot).
    This is something that is common for racing sheeting, but it may provide you a nice tuning for your common trips.

  9. #9
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    Default Re: Changing from laced to loose foot mainsail?


    Marianita has a loose-foot main on a fairly stout boom with sheeting aft.



    Things are a bit busy back there, but I'm used to it. Helps that the cockpit is small enough for me to reach everything from anywhere. Most of the designs that appeal to me have a small sea-going sized cockpit that would put mid-boom sheeting in the way of life aboard.
    Steve

    If you would have a good boat, be a good guy when you build her - honest, careful, patient, strong.
    H.A. Calahan

  10. #10
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    Default Re: Changing from laced to loose foot mainsail?

    Quote Originally Posted by kbowen View Post
    Some of the literature has it that a loose-footed sail had the advantage of being "brailed" up (haul the clew up to the gaff throat) to spill the wind when necessary, but this more appropriate in a completely boomless sail. My mizzen is loose footed to a boom and it is easier to get a reef tie around it than if i was dealing with it laced to the boom. Beyond those points I got nothing.

    Ken
    Gaffers have three main options for reducing sail; a traditional reef, "scandalize" the main by lowering the peak or "trice" by hauling the tack up the mast towards the throat. You're right, brailing is a boomless sail reduction method.
    Steve

    If you would have a good boat, be a good guy when you build her - honest, careful, patient, strong.
    H.A. Calahan

  11. #11
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    Default Re: Changing from laced to loose foot mainsail?

    I'd definitely go with loose footed myself. You probably won't be going for a vang/kicking strap but if you're going cruising there will be some dynamics to consider with preventers perhaps. I actually rig mine off a setup like a gaff span and that's on an alloy boom and bermudan sail, but then I run a pretty slack vang too to relieve stress on the gooseneck and boom. Wednesday night racers who go to sea often break booms and goosenecks with their vang tension. Sometimes a mast tragedy too.

  12. #12
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    Default Re: Changing from laced to loose foot mainsail?

    I do like a powerful vang, which mandates a powerful boom, even with end of boom sheeting
    edit to add: I need a powerful vang because centerline sheeting...

  13. #13
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    Default Re: Changing from laced to loose foot mainsail?

    You can try it and depending on how critical you are about peak performance it could work, but it's usually not ideal. On a typical modern cross-cut sail the foot and lower panel may be cut 180 degrees differently for a loose footed sail than it would be for a laced-to-the-boom version. In the case of a pre-computer hand-lofted cross-cut it actually was a 180 degree difference.

    A loose foot was designed with the bottom panel's top edge straight, joined to the straight edge of the next panel above it. Usually this seam terminated at or near the tack corner up front, thus it was called the "tack seam". The bottom of the foot panel was given a bit of round and often had a vertical split in it where a little broadseaming could be done to help cup the bottom edge just a bit (prevents flapping and creates an end-plate effect, preventing air from sneaking around under the sail and screwing up the pressure differential between the sail's two sides). It would also add some additional lower draft to what was the widest part of the sail. The rounded lower edge also looks nicer, for what it's worth.

    On a sail with the foot laced to the boom it was not unusual to loft out the sail the same way - straight tack seams and a nice foot round - but - before sewing the tack seam, you would flip the panel over and sew that rounded edge to the next panel up as the tack seam. I can remember back around 1980 when I was first learning to make sails reading the instructions over about 50 times, trying to figure out why in the hell you were supposed to design the sail one way and then sew the bottom piece on upside down.

    As it turns out, the straight edge was put on the bottom to lie neatly along the straight boom, and the curved panel edge sewn to the straight panel above it added the shape and draft to the bottom of the sail. The basic idea is still in play today, though computer-plotted sails usually plot curved edges on both pieces when creating something similar, and the foot edge may have a little bit of round as well. So the particular layout of the bottom may be acceptable as a loose foot in some cases and not so much in others.

    If you are also dealing with boom bend (especially with mid-boom sheeting) that can present a situation which is not ideal. Take your laced to the boom mainsail, head out on a windy day and sheet in hard, hoping to flatten the sail. As your boom bends downward in the middle, the lacing in that area pulls in the lower sail draft and really does help to flatten and depower the sail. If we then take the same sail and unlace it along the boom, sheeting in hard and bending the boom will move the sail's tack and clew corners slightly closer together. This will actually be adding lower sail draft, which is exactly not what you want in those conditions. It is certainly not the only factor which is shaping your sail, but it can be a contributing one. As a result, it might be a good idea to make sure that you have an easily adjusted outhaul tackle if you go loose-footed. Whether or not the foot will flap in a blow (even with a good outhaul) is hard to say. We usually try to avoid straight edges suspended out in space by themselves with no local anchoring points to a spar.

  14. #14
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    Default Re: Changing from laced to loose foot mainsail?

    Thank you for the in-depth explanation Todd.

    All: It has come to my attention that I may not have been clear in my first post, this is an exercise in forecasting a future project, not a current one. It is about trying to work out how to optimize an older gaff rigged design without losing the original "flavor". In 1930 they had some restraints imposed by the materials available, how/where can I do better now? Thanks to everybody for their comments so far.
    Steve

    If you would have a good boat, be a good guy when you build her - honest, careful, patient, strong.
    H.A. Calahan

  15. #15
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    Default Re: Changing from laced to loose foot mainsail?

    Steve, my Jewell is not an old design, but to my eye, looks like one. She carries a loose footed gaff main of 150sq feet.

    E06CBB7A-A014-476D-A368-D205BE1D2582.jpg

    Her boom is a departure from Vivier’s plans, which called for a solid wood spar—it is hollow, rectangular in section, with 9mm ply sidewalls and sitka stringers top and bottom (I forget if the Sitka is 1/2” or 5/8”). Light, stiff, and plenty strong. The rest of her spars are painted carbon fiber, shrouds are dyneema, as an example of traditional form in modern materials. That works fine for me aesthetically on the Jewell, which is a wood/fiberglass composite structure; the boat is also remarkably stiff and strong for it’s weight. It will be a fun and fascinating exercise to see where you strike the balance between newer materials and technology on one hand and traditional materials and methods for a new build of an older design. Parcelled and served dyneema rigging for something like this would be lovely, thank you:

    AA2E879E-ED49-412A-BC37-38A79C7207D8.jpg
    Best of luck, I’ll be keen to follow once you settle on a design and undertake the build. By the way, this is the original ANNIE by Fenwick Williams. She was moored in the Benjamin River last summer.
    Last edited by John hartmann; 10-24-2021 at 06:33 AM.

  16. #16
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    Default Re: Changing from laced to loose foot mainsail?

    Pretty much the boat of my dreams right there
    Steve

    If you would have a good boat, be a good guy when you build her - honest, careful, patient, strong.
    H.A. Calahan

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