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Barrel shape to broadseam

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  • 24 Dec 2017 00:03
    Quote
    Reply # 5647271 on 5646443
    Deleted user
    David Tyler wrote:
    Jami Jokinen wrote:This drawing by Erik helps a lot in understanding the concept.

    Arne, I'm more worried about possible hard corners (ugly and prone to damage) at the seams, more than the speculative performance issues.

    I'm worried by this drawing. It appears to show, neither broadseaming, nor darts/tucks, but a 'V' cut into the edge of the panel. I understand that this is how Slieve does it, adding an extra sliver of cloth to join the two edges; but it's easier just to fold the cloth over, sew, open up, flatten the excess cloth and sew again.
    I'm worried about the drawing, too.  And what the final sails will look like  :) 

    The drawing shows the design step of where I went from the 3D panel and laid it flat.  If one were to use David's darts/tucks, each "V" would represent such a tuck.  I (think I) did broadseaming though, by drafting separate sub-panels where each "V" is, adding seam allowance, then sewing the cloth sub-panels together using a sailmaker's seam. 

    My drawing shows that the cloth edge between each V is straight, and the one picture of David sighting down the edge after doing a tuck shows that the panel edge should come together straight across each tuck or broad seam.  If the shape is first drawn using the barrel method, then the edge is round.  After doing tucks, the edge will not be fair.  This may not be an issue when the sail is assembled if one cuts it straight again, but the initial amount of camber is decreased.  

    e     

    Last modified: 24 Dec 2017 00:04 | Deleted user
  • 23 Dec 2017 09:38
    Quote
    Reply # 5646811 on 5646208
    Anonymous member
    The cloth you are to use; is it in the soft league, or is it closer to real sailcloth?

    Arne

    Something in between, but I have no sample at hand until a week of two after christmas (I am not allowed to start a sailmaking mess at home before that :) )
  • 23 Dec 2017 07:43
    Quote
    Reply # 5646777 on 5643636
    Anonymous member

    This is one of the problems of being on the cutting - or should it be seaming? - edge of technology!  You have to invent the language.
  • 22 Dec 2017 21:30
    Quote
    Reply # 5646513 on 5643636
    Anonymous member

    Recognising the problem of naming a new (to me) method of shaping a panel I suggested two names which help to define the result. As the end result is exactly what you get when you use a broadseam, but there not being a seam then a 'Seamless broadseam' seemed apt. Equally, it is the same as a broadseam, but 'False'. My intention is to leave it to the readers to select the one they identified with best.

    I have no intension to mass produce sails, but if I want to get someone to make them to my specification I have already found that a 'professional' sailmaker will not entertain any sailmaking technique that is either not in their book, or will not produce a smoothly curved surface. They will not risk their reputation in making a 'lumpy' or a 'wrinkly' sail. I have had racing sails with small shallow darts along the boltrope at the foot of a mainsail, but I would not try to persuade a sailmaker to make the main shaping of a panel with anything less that a proper broadseam, so I tried to invent something which I thought they would accept. The results in my photos show smooth results that should be acceptable.

    It might become clearer when I update my write-up.

    Cheers, Slieve.

    PS. I've just been writing some notes for Jami, and have referred to the Seamless Broadseam as a 'Semi-broadseam', so there's another name to try out.

    Last modified: 23 Dec 2017 11:37 | Anonymous member
  • 22 Dec 2017 20:25
    Quote
    Reply # 5646483 on 5643636
    Anonymous member

    Then may I make a plea for your joint, Slieve, to be better named. It is not a seam, let alone any kind of broadseam, as recognised in sailmaking. In sheetmetal work, it would be called a butt joint with doubler, but as it is not generally used when sewing, I don't know of a name in this sphere . Maybe I didn't write clearly, but I understood from your 'Tip 5' exactly what you do to make this joint.

    I have no trouble with hard spots as a result of making darts/tucks. As my little drawing shows, I curve the first line of sewing such that there is no hard corner, and then I use a rubbing iron to flatten the excess cloth fully before sewing a second time. 
  • 22 Dec 2017 19:49
    Quote
    Reply # 5646475 on 5643636
    Anonymous member

    David wrote - “I'm worried by this drawing. It appears to show, neither broadseaming, nor tucks, but a 'V' cut into the edge of the panel. I understand that this is how Slieve does it, adding an extra sliver of cloth to join the two edges; but it's easier just to fold the cloth over, sew, open up, flatten the excess cloth and sew again.”

    Oh no I don't! (And for those who go to the pantomime, it's not behind me!) (Maybe some of our overseas members will not appreciate such UK seasonal jokes).

    In the 'Seamless Broadseam, or The False Broadseam' as described in Tip 5 the 'V' cut is a carefully shaped curved broadseam shape which is cut with very sharp scissors and butt jointed, getting its mechanical integrity back by sewing a double seam width patch on one side. With a soft material, and in dress making it may be satisfactory to fold in a dart, but with 'hard' sailcloth the start of the fold at the inner end of the dart will form a hard spot which will form a lump in the smooth shape of the sail. When making Amiina's sail I took a series of photos of this False Seam being made for future publication, (and filed away somewhere) and which you can see if you mail me.

    There are some useful photos in that file which should clearly show the broadseam and false broadseams being made, and how easy the operation is (after you've done a couple). These are to be included in my re-write of my notes which are supposed to be under way, but with a very low priority.

    Cheers, Slieve.
  • 22 Dec 2017 19:09
    Quote
    Reply # 5646443 on 5646106
    Anonymous member
    Jami Jokinen wrote:This drawing by Erik helps a lot in understanding the concept.

    Arne, I'm more worried about possible hard corners (ugly and prone to damage) at the seams, more than the speculative performance issues.

    I'm worried by this drawing. It appears to show, neither broadseaming, nor darts/tucks, but a 'V' cut into the edge of the panel. I understand that this is how Slieve does it, adding an extra sliver of cloth to join the two edges; but it's easier just to fold the cloth over, sew, open up, flatten the excess cloth and sew again.
    Last modified: 22 Dec 2017 19:32 | Anonymous member
  • 22 Dec 2017 18:51
    Quote
    Reply # 5646355 on 5646316
    Anonymous member
    Slieve McGalliard wrote:

    If the problem is with the curvature of the broadening of the seam then I suggest you read Tip 4 on page 49 of my notes. I know it's not well written but it should lead you to a shape that is a bit like the shape of a golf tee, flaring more rapidly as it approaches the edge.

    Ah, now I think I understand where the difficulty lies.

    I don't try to make calculations, but rely on hand-and-eye coordination. Look at this photo and then this photo to see how I simply form a softer corner by shaping it around my knee. And this is using hard sailcloth, where it is very difficult to make a hard corner, even if I wanted to. Using Outguard or Weatherguard, I don't think it would be possible to make a hard corner at all. 

    If in doubt on this or any other aspect of technique: make test pieces, using some offcuts. This is a hands-on craft skill that needs to be learned, and agonising over the theory will only take you so far.
  • 22 Dec 2017 17:48
    Quote
    Reply # 5646316 on 5643636
    Anonymous member

    No, you are not in the stupid question category, but are in the unclear asking area, Jami.

    It is all very simple, really, but only when you have worked your way through it once. The problem is that until you have you are not sure which question will give the required information. I'm trying to work out if you are asking about the shape of the taper in the actual broadening of the seam, or the curve round the outside of the barrel shaped panel.

    If the latter then David and Arne's answer about an arc of a circle from the luff corner to 70% chord point, with maximum height at the 35% chord point, followed by a straight line tangent from the leach corner to the arc is one that I have used and found good enough for amateur work, though will admit that I modify it as I have been playing with airfoil sections since the 1950's.

    If the problem is with the curvature of the broadening of the seam then I suggest you read Tip 4 on page 49 of my notes. I know it's not well written but it should lead you to a shape that is a bit like the shape of a golf tee, flaring more rapidly as it approaches the edge.

    Incidentally, I used the idea in Tip 5 for the 'seamless broadseam' on the last sail for Amiina and it gave a very good shape. However is was a bit fiddly to do, and I guess I would consider trying an angled shelf foot construction for my next small main sail panel with only one seam.

    If this does not give the answer, try again, and we'll get there yet.

    Cheers, Slieve.
  • 22 Dec 2017 16:32
    Quote
    Reply # 5646208 on 5646106
    Anonymous member (Administrator)
    Jami Jokinen wrote:This drawing by Erik helps a lot in understanding the concept.

    Arne, I'm more worried about possible hard corners (ugly and prone to damage) at the seams, more than the speculative performance issues.


    Me too, that  -  and the fact that I use horizontal cloth, puts me off from cutting into the cloth to make false  broadseams. 

    The cloth you are to use; is it in the soft league, or is it closer to real sailcloth?

    Arne

    Last modified: 24 Dec 2017 14:36 | Anonymous member (Administrator)
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