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Thread: Broadseaming theory

  1. #71
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    Apr 2012
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    Default Re: Broadseaming theory

    Thank you Todd,
    A great instruction.

    I will make a wooden mast. Is there any easy way to make a parted wooden mast? That was the idea in using the sailboard mast in the first place.
    What would be the dimensions of a wooden mast about 470cm long?


    For the sail I will go with the preshaped panels, broadseaming still feels a little intimidating.

    Marcus

  2. #72
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    Default Re: Broadseaming theory

    I usually suggest Iain Oughtred's spar specifications to my customers. That would put the mast at 1:52 in diameter of the length (measured from the partners or deck to the masthead). Below the partners it can taper to about 2/3 of that. Above the partners it retains about 90% of the full diameter at half height and then can taper to as little as 50% of full diameter at the masthead for that type of sail. So your full diameter would be around 90mm, half height about 81mm, 60mm at the heel and as little as 45mm at the masthead. I might go a bit fatter at the top for stiffness. Making sails which work well on bendy masts is much more difficult than those for a stiffer mast.

  3. #73
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    Default Re: Broadseaming theory

    What would be the luff round for such a mast?
    Mine is 90mm at 50% now.

  4. #74
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    Default Re: Broadseaming theory

    Usually about 2%-2.5% of chord width, plus a bit as a bend allowance, depending on how flexible the mast turns out to be. There is no real formula for bend allowance. It is up to the sailmaker's experience.

  5. #75
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    Default Re: Broadseaming theory

    So if the chord at 50% luff is 1440mm the curve would be 4cm + something....say 5-6cm? My 90mm are probably too much?

    Very confusing this is

    I guess I would have to know how much my mast bends first?

  6. #76
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    Default Re: Broadseaming theory

    It's not unusual to be building-in more curve for bend than for draft, but yes, it is nice to have at least a good hint of how much the mast will bend. There have actually been a couple instances over the years where I had customers lay the mast with boom attached on a roll of paper, tie the peak to the clew of the boom, tension it with simulated leech and mainsheet tension and trace the curve of the bent mast. These were mostly gunters though, where two spars of different diameters are partially overlapped, not both plumb, and they're held together with a rope. Good gunter sails can be very tricky to design.

    You can weight spars (usually by bridging them horizontally between the peak and partners areas on a mast, or both ends of booms or yards) and hanging a weight in the middle. Stretching a straight string above them allows you to measure the amount of weighted deflection at various points. Typically for small boats, the weight used is equal in pounds to about 1/3 of the sail's area in square feet. It's better than nothing, but it's little more than a rough estimate. You also don't always build in an allowance as big as the bend measurement. In some cases (like Sunfish-style or canoe lateen sails) those long skinny yards and booms bend like crazy. If you build in all the possible luff or foot round for bend allowance, the sail will be way too drafty and deep in light air when less bend is happening and performance will be poor. You have to arrive at some sort of compromise, usually based on previous experience. A Sunfish yard or boom will bend about 8". You usually build in about 3" of allowance for decent all-round performance - which will probably work better in some conditions than others, but it's the best you can do and is aimed at nice, medium sailing days.

    Yep, it gets confusing. Sailmaking has three distinct phases to learn. First is the design phase. Once it's lofted out, that part is pretty much done. Then there is the sewing part, and learning to do it cleanly because every stitch shows. Finally, there is the reinforcement and trim-out. Each phase will have challenges, and probably a few judgment calls. One reason I usually suggest that folks start with a pre-designed kit from a place like Sailrite is that most of the tough brain work is already done for you and you can begin sailmaking by concentrating on the assembly part. Which is plenty for now. I suppose that a free on-line sail design program can cut you a decent sail - if you know what to tell it, so that all the factors that need to be taken into account are there. There-in lies the rub for most beginning sailmakers.

  7. #77
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    Apr 2012
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    Default Re: Broadseaming theory

    Thank you,I measured the mast bent with 9kg and it is around 4cm.I'll just go with my 55mm luff curve. We'll see...Tyvek is cheap and I got enough for another sail.Another question that might sound stupid.Do you first sew on the smaller corner batches and then go bigger and bigger or do you start with the biggest?How long is the biggest corner relative to the edge and how many batches do you see on?I read all that somewhere...either in the instructions you sent or here.Can't find it anymore though.

  8. #78
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    Default Re: Broadseaming theory

    Smaller first. I learned after I finished my sails that the sides of the largest patch should be 10% of the sides of the sail.

    /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 :-)

  9. #79
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    Default Re: Broadseaming theory

    Tradition generally seems to be the second largest patch first, followed by the next smallest and the next smallest after that if there is one, and finally the biggest patch of all on top of all the rest. Then you sew through all of them. It helps to draw light pencil lines on the biggest patch that show the sizes of all the patches under it as sewing guides, because you often can't see them when sewing. Four layers of patching is usually enough on Dacron sails, though if it's a really narrow corner I may use more to get a bit more beef in that area. Shape is up to the builder, and around 10% of that edges overall length is good for synthetics. Cotton sails can have fewer and smaller patches due to the more stretchy nature of the natural fabrics. They tend to have less concentrated stress right at the stitch lines holding the patches on. For Tyvek you would want to be patching similarly to the way it is done on Dacron.


  10. #80
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    Apr 2012
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    Default Re: Broadseaming theory

    Perfect.
    Your sails are a delight to behold. Just beautiful.
    I just went ahead, cut and taped the sail that afternoon/evening.

    Had it hanging too but need to edit out my wife first

  11. #81
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    Mar 2014
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    Default Re: Broadseaming theory

    Todd,

    What's the reason for the concave curve of the foot?

    /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 :-)

  12. #82
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    Walney, near Cumbria UK
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    Default Re: Broadseaming theory

    Quote Originally Posted by mohsart View Post
    Todd,

    What's the reason for the concave curve of the foot?

    /Mats
    Because artists always paint sails like that?


    I'll get my coat.
    It really is quite difficult to build an ugly wooden boat.

    The power of the web: Anyone can post anything on the web
    The weakness of the web: Anyone can post anything on the web.

  13. #83
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    Default Re: Broadseaming theory

    That sail was built for a gentleman who was restoring an old Duckboat and wanted a period-correct looking sail rig for it. We hunted through old books and found mostly photos of spritsails on them, as well as a couple of lugs and even a small gaff sail. Many had that strange (but kind of cool looking) elongated clew corner with a hollowed foot - hollowed mostly to prevent flapping, I assume. It could certainly also have been built with some broadseamed foot round and would have been fine, but we decided to stick close to the old examples we found. This is the building plan I came up with for him. It does not show the broadseaming along the head and foot edges as I broadseam on the floor by eye as I baste the panels together. Having made a whole bunch of small, vertically-cut, four-sided sails over the last 35 years or so, I can pretty much broadseam in my sleep. The "owner's manual" that I sent out with the finished sail is the PDF below. Unfortunately, I never got a photo of the finished boat.



    http://webpages.charter.net/tbradsha...lans/!DUCK.PDF
    Last edited by Todd Bradshaw; 08-16-2017 at 04:03 PM.

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