Jib Sheeting Angle

Discussion in 'Sailboats' started by SuperPiper, Aug 17, 2006.

  1. SuperPiper
    Joined: Jan 2003
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    Location: North Of Lake Ontario

    SuperPiper Men With Little Boats . .

    Here is a photo of a etap28 that is borrowed from the pocket cruiser thread. The sheeting angle of the self-tacking jib is incredibly tight.

    What are the limits to sheeting angle? For a genoa with the sheets outside the shrouds, the limit is usually the shrouds or the spreaders. If a jib is sheeted too tight, the mainsail usually becomes severely backwinded.

    However, on the boat in the photo, the jib traveller is only the width of the cabin top. Wow, that looks like this boat can tack through a very tight angle.
     

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  2. Paul B

    Paul B Previous Member

    Modern non-overlapping headsails can be sheeted at 8 degrees off centerline or less, depending on the foils, hull shape, and sail shape. Modern ACC boats are as close as 6.5 degrees according to some sources.

    My boat of the same length is easily driven and sheets to 8 degree tracks (1.25 feet off center for a 9 foot "J") before inhauling. I believe the Melges 24 is about the same.

    With modern sails trimmed properly you will not see significant backwinding of the main. The big drawback to these rigs is how quickly the top of the jib twists off as soon as any sheet is eased.

    The hull shape of this Etap does not look particularly like something you would want to sail that close winded.
     
  3. SuperPiper
    Joined: Jan 2003
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    Location: North Of Lake Ontario

    SuperPiper Men With Little Boats . .

    So Paul, does the tighter sheeting angle imply a tighter tacking angle?
     
  4. Paul B

    Paul B Previous Member

    Generally speaking, yes. High pointing, and therefore narrower tacking angles, is also limited by the foil size and efficiency and sharpness of the hull form.

    You can't place the jib tracks of a Columbia 26 or Catalina 27 at 7 degrees and get a good result. The keels of those boats will stall and the full bows would need more power to push through any swell.
     
  5. RHough
    Joined: Nov 2005
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    Location: BC Summers / Nayarit Winters

    RHough Retro Dude

    Hey Paul,

    I'm adding new track for ball bearing Genoa cars to my old tubby Catalina 30. The standard placement was 1" sail track on the toe rail. The newer boats have the track inboard, curving to match the side of the house.

    It seems to me that I have 3 options:
    Run the track close to the house and curved (like the newer boats).
    Run the track in a straight line parallel to the centreline of the boat.
    Run the track in a straight line aimed at the forestay.

    Any advice on what would work best?
    The C30 has a D/L of about 300 and is far from slim :) What would be a good sheeting angle to shoot for? 10-12 degrees?
     
  6. Paul B

    Paul B Previous Member

    I guess I could ask "Why", after making a similar attempt in my youth on a Cat 27. We tried adding inboard tracks on top of the cockpit coamings, but the width of the spreaders was a limiter. I suspect this is the case with the 30 as well.


    You say Genoa, so I'll assume this is for your #1, hopefully a 155% sail. With the wide single spreader rig you'll find inboard sheeting of a #2 (say 135%) isn't going to work very well. Since this track is really only going to be for one sail I would limit the length to maybe 18". Your sailmaker should be able to hit that, with plenty of reserve for lead back in big breeze and lead forward in the light. You don't need 6 feet of track and fasteners you'll never use.

    Your best bet will be to get a scaled drawing of your deck plan. You'll want the chainplate location and spreader length sketched in. Now get the profiles of the foot shape and sail shape at the spreader, whatever foil your sailmaker is designing to. Lay the profiles on the deck layout and see where the tracks can really go without bending the foot around the shroud too much, or cupping the leech due to the length of the spreader. You don't want the leech of the genoa pointing at the main.

    If you can place the track adjacent to the cabin top and still have the sail fit around the rig measure the angle. I'll bet on a C30 it is probably 12 degrees or so. That might be the best you can do. Do the class rules limit this?

    I wouldn't angle the track toward the tack. As your lead goes forward you want a wider angle, not the same. Real race boats haven't angled the tracks along angle lines since the old IOR battlewagons in the mid-1970s. I think your side decks are narrow enough without having a big ball bearing track running across it.

    Have you thought about inhauling instead of tracks? Take a look at an Etchells or a Farr 40 to see the type of sheet-through-a-ring inhaulers they use.

    Weren't you building a 24 foot schooner that was going to wax a Melges 24? Maybe you should leave the old C30 alone and save the "go fast" gear for the M24 killer.
     

  7. RHough
    Joined: Nov 2005
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    Location: BC Summers / Nayarit Winters

    RHough Retro Dude

    LOL I ask myself that question almost daily! I have the keel off to fit SS studs to replace the pig iron or whatever they used in 1975, the bottom and keel are getting faired and profiled and the topsides painted this go 'round. I seem to be married to this boat. :)

    I have to agree, The #2 is a near useless sail on a single spreader rig. The new cars and track are for a PHRF max 155%. Why Catalina put an inboard track forward on the cabin top is beyond me. :)

    The shroud base is about 84" (Spreaders are 39") and the J is 13.2 ft. Sheeting to the rail is about 12 degrees for a 150 (20 ft foot and about 8 ft beam at the primaries).

    There are no class rules that limit deck hardware placement that I know of.

    Thanks for the advice. I'll sit down with my sailmaker and get some idea of profile before I take a drill to the boat. Drawing it out is the too simple solution that I overlooked. :(

    The Schooner project is waiting for a place to build and time to build it. I got a bit turned off when I found that getting it into the PHRF fleet may be a problem. Something about lifelines, cabin, and stuff like that. :) I'm not too keen on building a boat that I can't race.
     
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