optimum jib-main proportions

Discussion in 'Sailboats' started by dionysis, Aug 1, 2003.

  1. dionysis
    Joined: Jan 2003
    Posts: 258
    Likes: 3, Points: 0, Legacy Rep: 44
    Location: Tasmania, Australia

    dionysis Senior Member

    hi all,

    I wonder what people think about what the "optimum" jib to mainsail proportion is, for sloops. I guess that maybe there is no optimum.

    Designers have tried all the combinations. Does it depend on the hull proportions: beam to length? dsplacement to length ratio?

    I think that maybe 1:2.5 jib to main is what designers have settled on now. What needs to be taken into account to be able to make an informed decision?

    cheers dionysis.
     
  2. gonzo
    Joined: Aug 2002
    Posts: 14,462
    Likes: 643, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    Racing formulas encouraged ridiculously large foresails. As it became a fad, designs adopted the trend. A slightly overlapping jib helps to point higher. The separation of airflow on the main shifts aft, which allows it to be trimmed more inboard. Another advantage of a foresail is to aid in tacking. If you observe development racing classes where sail area is fixed, jibs are small.
     
  3. dionysis
    Joined: Jan 2003
    Posts: 258
    Likes: 3, Points: 0, Legacy Rep: 44
    Location: Tasmania, Australia

    dionysis Senior Member

    Another more reliable quote was 2.85: 1 proportion. You are right, that was my thought too.

    Does it make sense that, if the boat is heavy displacement, then it needs more power from its sails, so they need to be fuller. The fuller the sails the larger the jib to maintain pointing, wereas, say an easily driven light displacement boat can do with less camber in the sails and so will point higher, and so does not need such a large jib. Fast multihulls have no jib at all.
     
  4. Stephen Ditmore
    Joined: Jun 2001
    Posts: 1,388
    Likes: 44, Points: 58, Legacy Rep: 699
    Location: Smithtown, New York, USA

    Stephen Ditmore Senior Member

    As Gonzo suggests I think the answer depends on whether sail area is being measured, and how. If it's not, then I'd speculate that the optimum jib would be masthead, and as high aspect as the sailcloth will allow. I'd pair that with a relatively low aspect mainsail with a squared tip.

    I think the optimum location of the headstay / aspect ratio of the fortriangle might be effected by the mast section as well as the mainsail shape. I mean to suggest it might be different for a rig with a rotating wing mast vs a rig employing a fixed mast. I agree that mainsail shape might also effect the calculation, and therefore not only displacement, but wind speed, the boat's stability, and mast bend might also enter into it.
     
  5. brian eiland
    Joined: Jun 2002
    Posts: 4,948
    Likes: 179, Points: 73, Legacy Rep: 1903
    Location: St Augustine Fl, Thailand

    brian eiland Senior Member

    Jib-Main Proportions

    I would like for you to have a look at my predominiately headsailed rig at <www.RunningTideYachts.com> . It discusses some related subject matter

    I've also attached some related discussions to further my case.

    1) How Sails Work, the slot effect,Hall spars
    2) Tom Speer,forum response
    3) Cayard ProposaLtrExcerpt
     

    Attached Files:

  6. brian eiland
    Joined: Jun 2002
    Posts: 4,948
    Likes: 179, Points: 73, Legacy Rep: 1903
    Location: St Augustine Fl, Thailand

    brian eiland Senior Member

    Jib- Main proportions

    I had trouble with the attachments, so lets try again
     

    Attached Files:


  7. brian eiland
    Joined: Jun 2002
    Posts: 4,948
    Likes: 179, Points: 73, Legacy Rep: 1903
    Location: St Augustine Fl, Thailand

    brian eiland Senior Member

    Can't seem to get it all right this morning
     

    Attached Files:

Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.