Tuning a 9/10 rig

Discussion in 'Sailboats' started by farjoe, Jun 11, 2012.

  1. farjoe
    Joined: Oct 2003
    Posts: 163
    Likes: 1, Points: 18, Legacy Rep: 26
    Location: med

    farjoe Senior Member

    hi,

    The boat I race on is a 37 footer sporting a 9/10 rig. It has 2 sets of aft angled spreaders with standard fixed shrouds and inners and 1 adjustable backstay.

    The problem with this boat is that while it does fairly well in races at low winds it gets quickly overpowered above 13 knots.

    Flattening the main by pulling out the outhaul and cranking on the backstay is well nigh impossible. The middle to 2/3 of the sail remains full. Reefing is not a solution for racing until about 22 knots.

    The only affect of cranking on the backstay is to bend back the top 1m of the 14m mast.The rest remains rock solid and the main remains full.

    The only way we can get more curve on the mast is to loosen the inners which allows the mast to curve forward. However this results with too much sideways flop in the mast which seems dangerous.

    Are there any suggestions out there?

    regards

    joe
     
  2. sean9c
    Joined: Jan 2011
    Posts: 289
    Likes: 4, Points: 18, Legacy Rep: 35
    Location: Anacortes,WA

    sean9c Senior Member

    Sounds like your mainsail was just built with too much draft down low, call your sailmaker and ask him to go for a sail and take a look
     
  3. Paul B

    Paul B Previous Member

    You don't identify the type of boat, or the condition of the sail.

    If this is a class boat (beneteau, jeanneau, etc) your local sailmakers will probably have tuning guides available. They are also generally available on-line. These guides include rig tensions for various wind conditions, all to ensure the rig fits the cut of their sail.

    If the boat is not a class boat, a one-off, your sailmaker should be able to help with the setup. Maybe look at the tuning guides for similar boats and try some settings.

    Sounds to me like you do not have enough pre-bend. If you can slide the butt (step) back and chock the partners (at the deck) forward you can induce more pre-bend.
     
  4. farjoe
    Joined: Oct 2003
    Posts: 163
    Likes: 1, Points: 18, Legacy Rep: 26
    Location: med

    farjoe Senior Member

    the boat is an Elan and the sail is a carbon racing sail. Unfortunately the rig setting guide is not available, or at least I could not get it.

    However my question should be considered in general and not just for this particular type of boat. Anyway many boats of this range sport a similar rig.

    To rephrase my question, can rigs of this size and setup be altered to properly depower the sail as can be done on much smaller rigs and if not what are the options?

    Regards
     
  5. Mikko Brummer
    Joined: May 2006
    Posts: 546
    Likes: 67, Points: 28, Legacy Rep: 258
    Location: Finland

    Mikko Brummer Senior Member

    This is a problem of the modern rig with back swept spreaders and no runners. To support the forestay you need to use lots of backstay. If your rig is 9/10 (fractional ratio 90%), pulling the backstay will bend too much the topmast. You need a frac ratio of 93 to 95% to allow you to pull enough on the backstay without overbending the topmast. A carbon mast will work with lower frac ratios than an alu tube as it can be stiffened locally around the forestay attachment.

    This rig will need a mainsail with much less luff curve down low than the IOR times in-line rigs, but most sailmakers should have learnt that by now. There is one thing you can do to increase your mast bend down low without compromising the rig as in letting go the lowers: if you lengthen the forestay and let the mast lean more back (increase rake), the mast will not touch the cabin top as early as it's bending, resulting in a more even bend. This only works if the mast is keel stepped.
     
  6. Mikko Brummer
    Joined: May 2006
    Posts: 546
    Likes: 67, Points: 28, Legacy Rep: 258
    Location: Finland

    Mikko Brummer Senior Member

    It cannot be adjusted as readily as smaller rigs with lower frac ratios - this type of rig completely lacks the automatic behavior of a truly fractional in-line rig. You need to adjust the backstay as the wind changes on the water, and you need to adjust the shrouds in dock before you go out. For a fractional rig to work automatically you need a much longer topmast, in order of 80% frac ratio, to have the "lever" to bend the mast through leech loading of the mainsail. See the attachment on the "development" of the fractional rig.

    In the other attachment I've added a loading simulation from our boatbase for your Elan 37. With the rather narrow shroudbase the the back swept spreaders won't provide that much support for the forestay - hence you need to apply heeps of backstay (1,5 tons) to achieve a desired forestay sag of 1%.
     

    Attached Files:

  7. kenJ
    Joined: Jul 2005
    Posts: 349
    Likes: 5, Points: 0, Legacy Rep: 56
    Location: Williamsburg, VA

    kenJ Senior Member

  8. farjoe
    Joined: Oct 2003
    Posts: 163
    Likes: 1, Points: 18, Legacy Rep: 26
    Location: med

    farjoe Senior Member

    @Mikko, @Ken,

    Thank you very much for the info provided. Off to my corner now, to curl up and so some serious reading.

    Regards
     
  9. gonzo
    Joined: Aug 2002
    Posts: 15,408
    Likes: 999, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    Does the rig have a baby stay?
     
  10. farjoe
    Joined: Oct 2003
    Posts: 163
    Likes: 1, Points: 18, Legacy Rep: 26
    Location: med

    farjoe Senior Member

    I am unsure what the term baby stay stands for but I don't think so.

    The rig has the standard shrouds which I call the outers. These are called the verticals in the Selden link pasted above. Then there are what I call the innners which the Selden pdf calls the diagonals. The rig is similar to the Selden PDF diagram on page 8 except it is a 2 spreader affair and only one set of diagonals on the lower section of the mast.

    Since the vertical are...literally vertical from the deck to the second set of spreaders they have negligible effect in holding the mast in column athawrtship. Hence the inners( diagonals ) need to be very tight. But since they are also angled back they do not allow the mast to curve forward and reduce sail camber.

    Hence the problem.
     

  11. gonzo
    Joined: Aug 2002
    Posts: 15,408
    Likes: 999, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    A baby stay is a stay that attaches somewhere in the middle of the mast forward. It is temporarily attached to a fitting on the foredeck and it is used to force a curve on the mast and flatten the sail.
     
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.