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Thread: Lugsail design and construction

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    Default Lugsail design and construction

    I am in the process of building a 23’ Bolger Seabird 86 Dipping Lug Rigged sailboat as featured in Boats With An Open Mind (chapter 49).

    I have bought every book on sailmaking I can lay my hands on (including Emiliano Marino’s “Sailmakers Apprentice”, James Grants series of booklets, David Nichols traditional rigs book and Bowker & Budd’s “Make your own sails”).

    Only Marino does much more than mention Lug sails and the details he goes to are pretty sparse. Grants excellent booklets omit vertically cut sails almost completely and only provides a very brief comment on cross cut four sided sails.

    I was drawing a complete blank until I came across a thread on Broadseaming Theory where Todd Bradshaw provides massive insight and the most illustrative set of pictures on broadseaming a Lugsail I have found anywhere.

    I have have had quite a lot of experience sailing, making and repairing sails for myself, friends and neighbours. I am confident of being able to build good cross cut sails from scratch. However, vertical cut is still beyond my experience (except for assembling a Sailrite kit). I have never actually seen a Lugsail (cross or vertical cut) in real life so I’m not too sure of what I’m aiming for.

    As as I live in Chile, and no one else has probably seen a Lugsail in their life in these parts, it is pretty important for me to try and make the sail work as best possible, considering that many people will be reticent to the rig or, at least, condescending of me for wanting a boat with one.

    My doubts are mainly related to broadseaming and can be summed up as follows:

    - in most drawings, including Marino’s, the foot broadseam area seems to extend in a triangle from tack and clew, meeting 40-50% aft of the luff (which is where you want to position the fullness. How high should that go in the sail? What shape should those broadseams be?
    - understanding that a Dipping Lug is boomless, how much foot round is good to add and do you add additional broadseaming to support foot round?
    - where do you broadseam the head of a Lugsail. Marino seems to show the area around the throat only. In Todd Bradshaws series of pictures he seems to broadseam a triangle as in the case of the foot but shallower, although in the text of the thread I seem to understand otherwise.
    - are there significant design/construction differences between a Dipping and a Standing Lug sail? If so, which?

    I have a nice roll of Tanbark 6oz Marblehead Low Aspect sailcloth from Challenge to make the sail, and I’d rather not mess it up too badly. I was thinking of cutting to 27” panels but could go to 18” if it’ll make a significant difference in a sail this size

    sail measurements are:

    luff 14’1”
    head 15’
    leeck 22’7”
    foot 17’6”

    for a total of 276 sq ft.

    Appreciate your input.

    David
    Santiago, Chile
    Last edited by dcobb; 11-26-2017 at 07:59 PM.

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    Default Re: Lugsail design and construction

    Todds y,man on this issue. I bought a sail plain from Jim Michalak for lug mainsail off his Cormorant design, 207sq ft, which if i recall is the same dimensions as the main from Bolgers Martha Jane. Jims sail plans give the measurements for the broad seaming panels and any head /foot roach, leeches are usually hollow, im not sure how effective enlarging as a percentage of all dimensions might work on a sail. Lots of variables.

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    Default Re: Lugsail design and construction

    image.jpg

    Thought I’d show the sailplan for those who don’t have access to the book (or time to look for it)... Bolgers plan shows the sail with vertical panels 18” wide. I’ve penciled in 27” panels (which shows as every third panel split down the middle, with a first notion of broadseam length pencilled in at the relevant points.

    The guidelines in Marino’s book for Lugsail broadseaming don’t do much more than show this picture which doesn’t distinguish at all between Dipping, standing and balanced Lug sails.

    image.jpg

    I always thought of the line coming from the tack as bisecting it, but I get the feeling that takes the broadseaming too high in the sail. Rather than guessing I thought it’d be better to ask “those who knows”.

    The link to Todd’s photo instructional is found in the Broadseaming Theory thread. The relevant picture in the set seems to suggest broadseaming all along the head:

    49BE6BCA-1ED0-4C2B-A373-60D094254CEB.jpeg

    Appreciate your support.

    David
    Attached Images Attached Images
    Last edited by dcobb; 11-26-2017 at 05:31 PM.

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    Default Re: Lugsail design and construction

    I attach a picture of the sailplan with possible broadseam positions shown in dashed blue (following what I understand to be Todd’s method) but showing my take on Marino’s instructions in orange at the throat area.

    The blue solid lines represent 27” panels (half 54”) instead of Bolgers 18” originals.

    4DBB4523-D798-4BD4-9337-6BD5E5705CF0.jpg

    Comments, thoughts, experience, please...

    David
    Last edited by dcobb; 11-26-2017 at 07:48 PM.

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    Default Re: Lugsail design and construction

    Hi David -- I can't help you with the lugsail question, but I've always been fascinated by that design. I'd love to see some photos of the boat as it progresses. (And I'm sure others here would, too.)
    -Dave

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    Default Re: Lugsail design and construction

    I have only built sails, rather than designed them, though have converted/re-cut a few. I would say that looks in the ball park. Obviously more seams allows a more gentle transition between panels and a smoother shape. The Michalak sail has only 6 panels, the top broadseams are all 20in long and 1/2in wide, except the one at the throat 36in ling and 1 in. The foot seams are all 24in and 1in. Im not a rocket scientist or a sail maker, so cant tell you why it is drawn like this and if it could be improved, it might suggest the centre of the sail is a bit flat, compared to the other method. They do work as drawn though.



    I would certainly be happy to compromise on less seams to work (and chafe), for what might be a slightly compromised shape. No reason why a lug sail can not be a good performer. The above sail has a boom, a balanced lug, that might make some difference to how the sail is cut compared to the one on your design.

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    Default Re: Lugsail design and construction

    My guess would be that a higher peaked sail would need less broadseaming in the head.
    As for panel width, apart from smoothness (more seams to do broadseaming in -> smaller broadseams) the seams also help to keep the sail from deformation due to stretch. So with sailcloth prone to stretching, eg cotton or flax, narrower panels are preferable.

    /Mats
    My blog about my time as a boat building student and as a rigger apprentice http://kaptenmohsart.blogspot.se/ in Swedish only, but there are many pictures :-)

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    Default Re: Lugsail design and construction

    Quote Originally Posted by skaraborgcraft View Post
    ...The Michalak sail has only 6 panels, the top broadseams are all 20in long and 1/2in wide, except the one at the throat 36in ling and 1 in.
    I take from the scale drawing that Jim Michalaks sail is designed using full 36” wide panels.

    The long broadseam at the throat makes a lot of sense to me as it must serve to shape the entry. I’m not so clear about why he broadseams the head evenly. I seem to remember reading that he followed Bowker & Budds instructions on lugsail design. However they specify broadseaming to combat bias stretch rather than shape the sail. The BS length specified is consistent with their specification of 18” per 20’ of leech in the head and 3’ per 20’ of leech in the foot.

    Interestingly B&B are less clear about the width of the BS. They say “at the head seams should broaden so they become half as wide again as the ordinary seam. At foot each seam should broaden to twice as wide. In the case of loose footted sails the broadseams should be twice as wide as broadseams would normally be when a bolt rope is fitted and should reach up half as high again” (They expect seams on small sails (under 150 sq ft) to be 1/2” wide, so head BS would be 1/4” and foot BS 1/2” to 1” depending on whether the sail is roped or not).

    The last comment reinforces the fact that they are broadseaming to combat bias elongation rather than locate draft. (Probably because they were writing before stable Dacron/Terylene became the normal sailcloth.

    Input appreciated.

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    Default Re: Lugsail design and construction

    I will have to dig out my copy of B+B, but yeah, i recall most of the spec was based on traditional cloth construction, your modern dacron has nowhere near the same amount of stretch. There is some shaping of the head and foot on Michalak sails, which also helps with shape.
    The 2 sail makers i have worked with, both have been cagey (reluctant) about being specific about certain broadseaming issues, they both remarked about sailmaking being a "black art". and that experience is used rather than a specific formula; they could both be right, someone else made the remark that when sailmakers refer to the "black art", that it can be translated as they just guess, based on experience.
    Are you allowing any calculation for spar bend? I built my yard and tested it for bend as an input for the design process.

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    Default Re: Lugsail design and construction

    A seam without broadseaming combats bias stretch just as good as a broadseamed one.
    Also, "loose footed" means the sail isn't laced to a boom, it may still have roping. But I can see why one might have broader broadseams on a sail with no roping at the foot, especially if cotton/flax is used.

    /Mats
    My blog about my time as a boat building student and as a rigger apprentice http://kaptenmohsart.blogspot.se/ in Swedish only, but there are many pictures :-)

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    Default Re: Lugsail design and construction

    Nothing personal, but my advice is to steer clear of any of Michalak's sailmaking instructions! Those which I have seen tend to do things that no real sailmaker worth his salt would do (like making darts) or use some formulas he has made up which tend to be more confusing and less effective than just doing it the way it is normally done (and has been done for a long time) by professionals - and for no good reason. There is no benefit in trying to re-invent the wheel for traditional sailmaking. That drawing with the equal length broadseams quite clearly shows that he doesn't understand the way broadseams work, or what they are actually intended to do, and they would tend to make a foot and head which are more like a chunk of a cylinder than parts of a sail. I really do try to give the guy a break, but every time I look at one of his sailmaking plans there are glaring errors that clearly show that he shouldn't be trying to tell anybody how to design or build a sail.

    The various editions of Bowker and Budd are great for making natural fiber sails, but the additions made in later printings to include synthetic cloth are way out of date and don't apply very well to the characteristics of modern resin-coated and fairly stiff Dacron fabrics, so enjoy it and learn what you can, but choose what you use from that book with care.

    You are correct that instructions for making lugsails are pretty rare. Much of it is left up to the builder's experience and specific, set-in-stone formulas don't seem to exist. I don't think that anybody is trying to keep these things a secret, but the project of trying to generate an instruction manual applicable to lugs in general would be a big and tedious task with a very limited commercial potential. You don't make much money writing boat books in the first place, and boat books about such obscure and limited subject matter make even less (don't ask me how I know this ).

    Some things pertinent to your specific sail (at least the way that I would do it):

    That's a long luff and luff tension is critical on lugs. I would hollow it at a rate of around 1" of hollow per every 10' of luff length, so about 1.5" for a 14' long luff, deepest hollow about 45% of the luff height above the tack corner. Convex luff round on this type of sail will usually just flap or wander back and forth, so it is to be avoided. Short-ish luffs can be cut dead straight, longer luffs benefit for a bit of hollowing to help keep them tight when under tension. The luff tape should be doubled for extra stretch resistance or the edge can be roped for even more strength, but somehow you must create a strong and stretch-resistant luff edge which will stand up to substantial downhaul tension.

    Leech - hollowed at a rate of 1" per 6' of leech length, centered mid leech. This prevents flapping as the sail ages. Hemmed, bound, or using a tabling will all work to finish it off, though tablings can be rather difficult with the current stiffness of most Dacron. (Tabling = fold about a 1/2" hem on the leech and on both sides of a narrow vertical strip cut to a similar curve, which is then sewn on top of the edge with all of the hem folds hidden inside, between them.)

    Foot: pretty much anything except straight and it can be hemmed, bound or roped. The amount of foot round really isn't critical, though I wouldn't go overboard. For a sail that size (almost 18' on the foot) I'd probably add maybe four or five inches of round with maximum depth about 45% aft of the tack and a fairly flat run-out aft toward the clew. It's literally a case where you want to generate a nice looking curve and the exact amount of depth isn't very critical. A straight foot works fine as well, but tends to look chopped off and strange. You could even hollow the foot if desired, like I do on my "squgsails" which are lugs made to mimic squaresails to some extent, but a nice roud would be more typical.

    Squgsail (balanced lug wearing squaresail disguise) with hollowed luff, leech and foot:



    The reason to broadseam spread along the head, rather than to concentrate broadseaming near the throat corner is that the throat area on a lug or spritsail won't tolerate an awful lot of sewn-in shape and still set properly. It tends to create a "bag" up at that corner which won't go away and spread out the fullness. The broadseam area at the top of one of these sails doesn't need to be very big and the broadseams aren't very long, so as a result, they won't be particularly wide, either. We're trying to give the head a little bit of a cupped shape, bringing the drafty upper sail shape back in to meet the spar, but we don't want to overdo it and make some sort of deep cupping that won't set right. The head will have a bit of round added for upper sail draft (maybe 2" or so on a sail that size) and will have additional round added (probably at least that same amount) as a spar bend allowance. Both these things (draft amount and bend allowance for lugsail heads) to my knowledge have not been specified in any books that I have seen. Unfortunately for the beginning sailmaker, they seem to be things that you learn by doing them and slowly getting a feel for what works. Shaping lugs is not so much an "art" as it is a chance to learn through practice and repetition.

    I generally place the peak of the lower (foot) broadseam triangle about 45% aft (45% is kind of a magic figure that tends to be safe for a lot of various measurements on traditional sails) and at a height where I think the deepest part of the sail's draft will be. The broadseam triangle then extends from that spot down and outward to the tack and clew corners. Any seam that runs through that triangle will be broadseamed - unless I'm working with really narrow (like 6"-8" wide) panels, where I may broadseam every other seam. From a practical standpoint, panel width is partly a function of economy because Dacron isn't cheap. The yardage will be split into widths that work with the fabric's raw width, so as not to waste it with a bunch of skinny, cut-off strips.

    Many narrower panels use smaller broadseams than fewer wider panels would, as we want the same basic sail shape regardless of how many panels we use. If you must have a formula for the amount to broadseam a seam, the safest is probably to increase the seam width by around 1/2" for every 30" of seam length inside the broadseam zone, written for panels of 36" wide cloth (which was "standard full width Dacron for a while). Splitting to 18" panels would change it to 1/4" per 30" of seam length inside the zone, 9" wide panels +1/8" per 30", etc. Even those amounts will vary some with different levels of cloth firmness and stability. Softer fabric is less dimensionally stable and requires less broadseaming than firmer, more stable cloth.

    The last few inches before your broadseam meets its end at the head or foot edges, you increase the broadseam overlap rate a little bit. This helps to generate the slight cupping along the edge, but keep it pretty slight. You don't want to hook those edges with too much cupping. For the broadseam triangle up top, I might come down 20"-24" or so for the deepest spot on the triangle. I'll usually try to pretty much line up the peaks of both the upper and lower broadseam triangles,so that a line drawn between the would pretty closely follow the same angle as the panel seams.

    For that sail, I'd probably split the cloth to 18", rather than 27", mostly because the narrower panels will look more classic, though either way would work. The difference in construction time isn't that much, and most of the tedious work is still in the trim, not the paneling. If you have reef lines, the grommets could also be placed at the 18" seams to look orderly.

    I hope this at least helps somewhat, and I'm sure other sailmakers may do some of these things differently, but those are some of the issues I would be dealing with to build such a sail, and there wouldn't really be an awful lot of difference between the basic elements of dipping, standing and balanced lug designs and construction. Perimeter shape, rigging details and trim-out might vary some, but they'll be pretty similar.
    Last edited by Todd Bradshaw; 11-27-2017 at 08:35 PM.

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    Default Re: Lugsail design and construction

    Quote Originally Posted by skaraborgcraft View Post
    ... that when sailmakers refer to the "black art", that it can be translated as they just guess, based on experience.
    Are you allowing any calculation for spar bend? I built my yard and tested it for bend as an input for the design process.
    I agree that experience is often very undervalued. Reading a book about sailmaking won’t make a sailmaker any more than reading a book about sailing will make you a sailor. An artists guess is, at the very least, an informed one. However certain arts (black or otherwise) are at risk of being completely lost if people don’t pass them on/write them down/share them. If we can document basic processes from enough people with experience we should be able to help people in the future avoid costly mistakes and enable them to approach the art more confidently. In in the end, it’s the great artists that are not afraid to teach their art and are proud of their pupils successes.

    Sometimes its simply people who take an jnterest in something (without being artists themselves) who can document processes enough to avoid the information being completely lost. (Edgar March’s documenting the Sailing Drifters is a case in point directly related to Lug sails).

    Re spar bend: yes I plan to compensate for spar bend with head round. However, as I’m planning to rig using a peak halyard (per Bolgers suggestion in BWAOM) I'd appreciate input as to whether this should be factored into the amount of head round.

    David.

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    Default Re: Lugsail design and construction

    Quote Originally Posted by Todd Bradshaw View Post
    I hope this at least helps somewhat, .
    An understatement if ever I saw one. Already greatly indebted to you. Thank you so very much.

    I really appreciate the time dedicated to writing all that down as well as the willingness to share.

    Should I factor in the peak halyard when allowing for spar bend or does a peak halyard not actually support the yard when the sail is drawing? Where do you center the head round? Also 45% aft or where the halyard is supposed to be attached to the yard?

    I built a lateen for a Sunfish from basic Marino principles as a test sail and gifted it to a small sailing club close to where I sail. People were wary of the fact I had used 6 panels rather than the traditional Sunfish 5 panels (not to mention that the dimensions came out very slightly shy of class standard. However, to everyone’s surprise, it consistently points better than other sails (including a new factory made class one). My conclusion is that there is a lot more to sail desigb than immediately meets the eye, and that mass produced sails are not necessarily cut particularly efficiently.

    Consequently i would echo your comment that sail design is clearly open to experimentation. Lug sails probably more than most.

    I like your squagsail btw. What boat(s) do you make them for?

    David

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    Default Re: Lugsail design and construction

    The squgsail in that photo was designed and built for Clint Chase. He wanted it to be used mostly just downwind on one of his boats designed primarily for rowing. For that use we didn't have to worry about losing potential pointing/tacking angles by dropping the peak angle and though it was kind of a neat concept.

    I'll normally attach the halyard 35%-40% aft on the yard for starters. Then it's a matter of experimenting to find the location that sets the sail best. The yard really does need to be tail-heavy to stay stable. If you get the halyard tied too far aft, the throat will dip and the peak go skyward every time you ease mainsheet tension. I suppose that might at times be handy on a dipping lug, but I doubt you really want that sort of balance between tacks. You will find that in comparison to a lot of common sailboats, hanging up a lugsail is a bit more like flying a kite from a pole. You are hoisting a somewhat self-supporting contraption which is being held in place and at a certain attitude just by a few strings, which are infinitely adjustable. Despite this, it can work quite well when done properly, but it will likely take a bit of experimentation to find the sweetspot(s).

    I have no idea what a peak halyard would do to the program. My gut feeling tells me that if it is going to work and be worth having, the mast is going to need to be unusually tall - substantially taller than a typical lugsail needs. That means more weight up there where you need it the least. It would need to be a very big performance improvement for me to justify it. I kind of doubt that it would do much to reduce yard bend, but I've never seen one used so I can't say for sure. If they made a true improvement on lugsails I would think we would see a lot more of them.

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    Default Re: Lugsail design and construction

    I hope this at least helps somewhat...
    Understatement of the year, if not the decade.

    Thank you, Todd.

    Alex

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    Default Re: Lugsail design and construction

    Subscribing!

    (as I plan to make Todd`s standing lugsail for my Argie 15)

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    Default Re: Lugsail design and construction

    Thanks again Todd

    I have attempted to put your comments into an updated sailplan as follows:

    FB058FEB-C7D5-467B-87C0-659858EDDB2E.jpg

    The black marker line in the lower portion of the sail marks the approximate fore-aft 45% position, thereby dictating the apex of the lower broad seam triangle. The decision regarding height of the lower broadseam area remains to be decided but I have pencilled in heights of 4, 5 and 6’ and highlighted the broadseams for the taller triangles. In all cases, foot broadseaming all but disappears with the first drawn reef and completely disappears with the second reef.

    The head broadseam triangle is drawn to apex at around the same line, but this places the apex a seam line aft of the apex in the lower triangle.

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    Default Re: Lugsail design and construction

    On the topping lift question, somewhere in his writings Bolger mentioned used a topping lift on a balanced lug to control the yard when lowering the sail. As I understood it, the line would not be under tension once the sail was set, and the mast would not need to be longer to carry the lift.

    In 100 Small Boat Rigs, Bolger shows lazyjacks on his balanced lug illustration. He also notes that one would have to grab the tip of the yard and center it over the boom before the lazyjacks would cradle it. I suppose on a sail as large as the one under discussion, a topping lift and lazyjacks could both be rigged for maximum control over the sail when setting and dousing. I have a 75 square foot balanced lug on my Whisp, which is easy to manhandle and the yard in any case doesn't have enough weight to do real damage. But on a blustery day, it does thrash around on its way down, and it does want to drop into the water. On a bigger boat I think I'd want to contain the yard as much as possible.
    -Dave

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    Default Re: Lugsail design and construction

    Thanks Todd

    The questions that spring to mind from the above are as follows:

    Quote Originally Posted by Todd Bradshaw View Post
    The broadseam area at the top of one of these sails doesn't need to be very big and the broadseams aren't very long, so as a result, they won't be particularly wide, either. We're trying to give the head a little bit of a cupped shape, bringing the drafty upper sail shape back in to meet the spar, but we don't want to overdo it and make some sort of deep cupping that won't set right.
    1) Both Marino and Grant specify shaping guides for broadseams emulating a golf tee where the broadseam width is always specified at the widest point (i.e. the edge of the sail) and most of the broadening occurs in the 25-50% closest to the edge. I have struggled to get any shape at all in the 50% furtherst from the edge when the total calculated broadseam width is anything less than 1/8". I find I can only produce any shape in the "bit closest to the edge" or end up with something very close to a straight line (with very little noticeable increase in curvature at the edge).

    2) In the head broadseam closest to the throat, my sketch produces a broadseam length of about 6". At a broadseam rate of 1/4" every 30" that produces a 1/20" (i.e. 1.27mm) broadening in the 6" length. How do you get any shape?


    Quote Originally Posted by Todd Bradshaw View Post
    The last few inches before your broadseam meets its end at the head or foot edges, you increase the broadseam overlap rate a little bit. This helps to generate the slight cupping along the edge, but keep it pretty slight. You don't want to hook those edges with too much cupping.
    3) Should I understand that you actually go over the rule of thumb broadseam rate to enable the "cupping" effect, or are you referring to the "progressive broadseaming effect" that Marino and Grant illustrate as the golf tee shape, keeping the defined width at the outside edge end of the broadseam?


    Quote Originally Posted by Todd Bradshaw View Post
    For the broadseam triangle up top, I might come down 20"-24" or so for the deepest spot on the triangle. I'll usually try to pretty much line up the peaks of both the upper and lower broadseam triangles,so that a line drawn between the would pretty closely follow the same angle as the panel seams.
    4) In the sketch I have shown the foot triangles and blue head triangle with their apex at the 45% position. However, this leaves them one complete panel misaligned with respect to your last comment. If I extend the point at the head to fall on the same seamline, it ends up much closer to the 40% mark (see darkened area). This also lengthens the broadseams nearer the throat (extension of broadseams shown in black). What do you suggest here?


    A couple of reflections. Not really questions, but welcome comments anyway:

    Quote Originally Posted by Todd Bradshaw View Post
    the throat area on a lug or spritsail won't tolerate an awful lot of sewn-in shape and still set properly. It tends to create a "bag" up at that corner which won't go away and spread out the fullness.
    Analysing the plan, I can't help noticing that the "head broadseam triangle" follows a 30% fore-aft position from the peak. I wonder if that isn't experience allowing for the fact that the yard will tend to fall off, so treating the top of the sail as a triangular sail but moving the draft forward in order to compensate for twist.

    This natural twist would also explain why the throat area doesnt like the shaping it would appear to need on paper.

    I assume the nature of the loose footed lugsail is that the foot will naturally assume camber which the wind will blow into it, whereas the peak will always tend to fall off to windward. The broadseaming in the foot provides camber when the wind isn't strong enough to do this by itself.

    As you reef, the camber generating effect of the wind becomes sufficient by itself, so reefing not only reduces sail area but also flattens it out. The head broadseam triangle tends to position the ensuing camber, while the yard falling off flattens the aft top section of the sail, at the same time increasing the entry angle at the luff, so remaining comparatively powerful.


    Your kite analogy extremely clear. I'm doing everything in my power to increase the odds in my favour of flying the kite successfully while most people in my boating world are deciding between being condescending or looking forward to my failure.


    Appreciate thoughts.

    Thanks again, David
    Last edited by dcobb; 11-28-2017 at 02:43 PM.

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    Default Re: Lugsail design and construction

    Quote Originally Posted by dcobb View Post
    Thanks again Todd

    I have attempted to put your comments into an updated sailplan as follows:

    FB058FEB-C7D5-467B-87C0-659858EDDB2E.jpg
    How to understand the blue and green marks? It looks like you intend to make the broadseams broader in the middle of the sail, but you clearly don't mean that.

    Personally, I'd put the reef points for both reefs on the same seams. Looks neater to my eye.

    /Mats
    My blog about my time as a boat building student and as a rigger apprentice http://kaptenmohsart.blogspot.se/ in Swedish only, but there are many pictures :-)

  21. #21
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    Default Re: Lugsail design and construction

    Quote Originally Posted by mohsart View Post
    How to understand the blue and green marks? It looks like you intend to make the broadseams broader in the middle of the sail, but you clearly don't mean that.

    Personally, I'd put the reef points for both reefs on the same seams. Looks neater to my eye.
    Mats

    The green and blue marks illustrate how far the broadseams would reach IF the apex of the foot broadseam triangle is increased from 4' to 5' and 6' respectively.

    Re reef points: I would tend to put reef cringles every seam so as to end up with points every 18". I find more ties make it much easier to keep the sail tidy and put less strain on each. You can always use less if you want to. The reef points shown are straight from Bolgers sailplan as he drew them to show the reef lines rather than a construction plan on my part.

    David

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    Default Re: Lugsail design and construction

    Right, but the lines are broader closer to the center of the sail.

    Every or every other seam or whatever is fine, but you/he have the first reef at seams #3, 6, 9 and second at seams #2, 4, 6, 8, just looks messy to me. But OK, not how you'll do it.
    Regarding strain, the reef points should normally not need to take much strain to talk of; they are typically placed a bit lower than the invisible line between the tack and clew for the reef in question.

    /Mats
    My blog about my time as a boat building student and as a rigger apprentice http://kaptenmohsart.blogspot.se/ in Swedish only, but there are many pictures :-)

  23. #23
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    Default Re: Lugsail design and construction

    1) Both Marino and Grant specify shaping guides for broadseams emulating a golf tee where the broadseam width is always specified at the widest point (i.e. the edge of the sail) and most of the broadening occurs in the 25-50% closest to the edge. I have struggled to get any shape at all in the 50% furtherst from the edge when the total calculated broadseam width is anything less than 1/8". I find I can only produce any shape in the "bit closest to the edge" or end up with something very close to a straight line (with very little noticeable increase in curvature at the edge).

    2) In the head broadseam closest to the throat, my sketch produces a broadseam length of about 6". At a broadseam rate of 1/4" every 30" that produces a 1/20" (i.e. 1.27mm) broadening in the 6" length. How do you get any shape?
    3) Should I understand that you actually go over the rule of thumb broadseam rate to enable the "cupping" effect, or are you referring to the "progressive broadseaming effect" that Marino and Grant illustrate as the golf tee shape, keeping the defined width at the outside edge end of the broadseam?
    You seem to be expecting to see shaping dramatic enough that you can see it on a scale drawing. That isn't likely to happen. The "golf tee flare" (at least the way that I do it) is added onto the width that would be calculated. If, for example, I was planning a long broadseam consisting of a 1/2" seam overlap increase, to be added to my normal 1/2" wide seam overlap, it would be figured as if that seam would end up being 1" wide at the edge of the sail and the taper would be a perfectly straight line. However, when actually basting the panels together I'd aim for that taper and then start flaring in a bit more overlap starting maybe six to eight inches out from the edge on a broadseam that long. For a 6" long broadseam near the throat you'll still have a little bit of flare, but it won't look like much, and doesn't need to be.

    Disclaimer: I don't actually calculate broadseams and haven't for at least 20 years. I lay out my broadseam triangles on the floor by eye with tape and do all my broadseaming by eye. On a cross-cut sail we can adjust the entry angle at the luff by adjusting the severity of the golf tee flare. More flare gives a more rounded entry, less flare a flatter one. On vertically cut sails we don't have that luxury as we don't have many, if any, seams striking the luff at a good angle for broadseaming.

    Sail shaping is actually a product of a bunch of fairly subtle changes. Notice how basically flat this lugsail looked when I hung it up from a tree to get a look at it. Out on the water though, it has pretty nice shape. You can also see some of the broadseams on the left photo.



    4) In the sketch I have shown the foot triangles and blue head triangle with their apex at the 45% position. However, this leaves them one complete panel misaligned with respect to your last comment. If I extend the point at the head to fall on the same seamline, it ends up much closer to the 40% mark (see darkened area). This also lengthens the broadseams nearer the throat (extension of broadseams shown in black). What do you suggest here?
    The location of the peak of the bottom triangle is much more critical than that of the top triangle. I'd just place the peak of the top triangle roughly along a line from the peak of the bottom one and parallel to the leech. We're looking for a situation where the deepest part of the chord widths line up pretty well as you go up and down the sail and our triangles should ideally peak at those deepest chord areas. Keep in mind though, that it is certainly possible to overthink this stuff. There are no hard and fast formulas for much of it that would make lugsail design a simple matter of following some instructions. There wouldn't be much need for sailmakers if anybody could just crank one out with ease and no practice or experience.

    Analyzing the plan, I can't help noticing that the "head broadseam triangle" follows a 30% fore-aft position from the peak. I wonder if that isn't experience allowing for the fact that the yard will tend to fall off, so treating the top of the sail as a triangular sail but moving the draft forward in order to compensate for twist.

    This natural twist would also explain why the throat area doesnt like the shaping it would appear to need on paper.

    I assume the nature of the loose footed lugsail is that the foot will naturally assume camber which the wind will blow into it, whereas the peak will always tend to fall off to windward. The broadseaming in the foot provides camber when the wind isn't strong enough to do this by itself.

    As you reef, the camber generating effect of the wind becomes sufficient by itself, so reefing not only reduces sail area but also flattens it out. The head broadseam triangle tends to position the ensuing camber, while the yard falling off flattens the aft top section of the sail, at the same time increasing the entry angle at the luff, so remaining comparatively powerful.
    I'm not sure any of that is true (overthinking maybe?). I do know that the reason the throat area won't tolerate a lot of shape has nothing to do with twist. It is purely a mechanical problem. Most of the shaping which is done on sails is either reducing or increasing the amount of fabric in a localized area and this then affects a much larger area, spreading out whatever effect it generates. The throats of four-sided sails are not capable of spreading out excessive shaping there and you generate a bag, a wrinkle that won't pull out, or some other distortion - and the distortion is what gets spread out into a bigger area. Not good.

    Broadseaming in the foot both generates camber in the foot and positions it. Wind pressure alone (along with eased outhaul tension) can generate camber, but can't shape the foot or move our maximum sail camber up where we want it (or create a bit of end plate effect at the bottom of the sail).

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    Default Re: Lugsail design and construction

    Thanks Todd

    I’ll plead guilty to “overthinking” any time. It’s a good concept. I’d rather overthink than be thoughtless, but thinking about it, I probably do think too much rather than running the risk and then learning from my mistakes...

    I suppose the advantage of broadseaming over woodwork is that the old “measure twice cut once” doesn’t apply. In broadseaming you can always take out the seam and redo it if you really get it wrong.

    Rereading your posts both here and on the Broadseam Theory thread, and looking at the pictures both of your sail above (really useful) and your broadseams on the series,

    Quote Originally Posted by Todd Bradshaw View Post
    If it helps, I have a photospread of making a lugsail here.

    http://s1303.photobucket.com/user/To...?sort=9&page=1

    I get the impression that your vertical broadseams take a shape more as described in books for shallow entry horizontal broadseams. I should have studied that picture harder and thought less.

    FCF5B7EC-884B-4C48-96AB-CCC8BC9DF875.jpeg

    I love your use of seamstick to draw the broadseam shape... That is so much easier than drawing them... and faster... but I would probably never have thought of it...

    I think you´ve helped me far enough now to force me to stop thinking (fretting) and start doing...

    The only real doubt I have left is how high to take the foot broadseam triangle.
    Last edited by dcobb; 11-29-2017 at 07:15 AM.

  25. #25
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    Default Re: Lugsail design and construction

    The middle one looks about right to me. As for taking out and changing broadseams, it's actually a hell of a lot of work because the broadseaming is done so early in the building process. Changing a broadseam generally alters the length of that edge of the sail, which will likely then require also changing the length of the trim on the edge (roping, for example). I think it was Marino who said something like "sailmakers frequently alter the broadseaming on finished sails once they're done". That has never been my experience, and you have to remember that the sail will actually be a slightly different size after you are done with the changes. So the less you have to fiddle around with existing seams, the better. Also, the old needle holes never go away and are ugly.

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