luff round dimensions

Discussion in 'Hydrodynamics and Aerodynamics' started by kim s, Oct 11, 2012.

  1. kim s
    Joined: Apr 2009
    Posts: 76
    Likes: 3, Points: 0, Legacy Rep: 42
    Location: essex, uk

    kim s Junior Member

    I have had a new sail made for my old design Hartly Lively 28 trimaran

    The mast is an ally mast that has been made to exactly the same length as the original box section wooden mast, so its VASTLY overigged. 3 spreaders with diamonds in between all of them.

    right I have NO prebend due to the section and diamond rigging on the mast.

    the sail has been cut with a 4" round/prebend.
    Is that right?????

    the manufactures say it is, a sail maker friend says it isnt.

    the sail is standard short battens, in Dacron. so no laminates as the boat isnt worth it
    I stated on the orignal forms NO PRE-BEND so they did know, and also left pictures of the boat and mast for reference
    the sail seems very full and the fullness moves aft in a gust which just loads up the helm and stuff the leeward hull into the water with no real increase of speed.

    I have used the sail for approx 200 miles 0r 2 long weekends and so it didnt go straight back, as all sails take a bit of getting used to and it could have been my incompitance, but in the end, back it went and they say they have sorted it but the work they say they have done, they dont state they have reduced the luff round.
    any advice would be greatly appreciated

    Kim
     
  2. fdonmedway
    Joined: Oct 2012
    Posts: 2
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Kent, UK

    fdonmedway Archie

    http://www.hartley-boats.com/lively28.html
    shows two spreaders with top middle and lower shrouds the lower being two sets two forward and two aft.

    You could try easing the aft lower shrouds to allow the mast to move forward in the middle when the wind is strong. Though you really need something to push the mast forward. Tightening the fore lowers might be OT as it would be permanent.

    Archie
     
  3. kim s
    Joined: Apr 2009
    Posts: 76
    Likes: 3, Points: 0, Legacy Rep: 42
    Location: essex, uk

    kim s Junior Member

    Hi Archie

    Unfortunatly, the mast in picture shown on the link is not what is on the original drawings.

    I dont have any lowers. the cap shrouds go from 3/4 up to the outer hulls. there is a masthead forestay and an inner stay attached to the cap shroud position
    a back stay and running back stays which I dont use unless the inner headsail is up
    and thats it.

    the whole thing is held in column by the diamonds.
    there is NO aft sweepback on the spreaders
    a tree trunk if ever I saw one:eek:

    Kim
     
  4. fdonmedway
    Joined: Oct 2012
    Posts: 2
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    Location: Kent, UK

    fdonmedway Archie

    Hi Kim

    In other words you have two forestays with runners to hold the lower and back stay for the upper. If you ease the upper forestay and tighten the backstay it will tend to bend the mast. OK 4" sounds a lot with a stiff mast but it may help. Also harden the main halyard in a blow or use a cunningham.

    I must agree that it is easier to put fullness into a sail than get it out. It may get a boat going marginally faster in medium conditions but unless you're racing it's all a waste of time. Simpler to cut flat to start with.

    Essex isn't far from the Medway. How far up? See you on the water sometime.

    Archie
     
  5. kim s
    Joined: Apr 2009
    Posts: 76
    Likes: 3, Points: 0, Legacy Rep: 42
    Location: essex, uk

    kim s Junior Member

    Luff round

    Hi Archie,

    I have tried easing the upper forestay but then the diamonds neaded sorting as this was allowing the mast out of coloumn. at the time I could not get up the mast but now have bought some climbing equipment and some one showed me how to use the old prussic knott. I will have to spend a bit more time on it.

    I am just a bit upsett really that the sail manufacture gave me all the sales talk on the sails, how they made a lot of sails for multihull charter fleet blah blah blah.
    now it seams to be my fault they could not cut the sail right in the first place.
    I wont name names yet as this might get a bit messy but I am hoping to pick up the sail today and we shall see.

    I am in the Blackwater so not far from you.
    I promised myself to get over to the Medway as its one place I have never really explored.down the Swale to the pub on the north side and stopped off in Queenborough, but thats it.

    cheers for the advice. I had forgotten I played with the mast when Ifirst put it up. so will know re-visit the idea

    KIm
     

  6. messabout
    Joined: Jan 2006
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    Location: Lakeland Fl USA

    messabout Senior Member

    Attentive sailmakers will insist that they be provided with the bend characteristics of the mast before they start cutting cloth. Stiff masts do not need much if any luff curve. Draft is achieved with judicious broad seaming of the panels.

    Four inches of round is quite a lot for anything but the tallest luff or a bendy mast.. Performance from a sail with too much luff curve will be just as you have described. Draft moves aft leading to weather helm and poorer performance. Generous curve and easily controllable mast bend is the stuff of racers but less desirable for cruising boats.
     
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