sprit rig cutter & weather helm

Discussion in 'Boat Design' started by Oldlugger, Jan 18, 2009.

  1. Oldlugger
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    Oldlugger Junior Member

    Hi I am new to this forum but I belive it was one of the members that was well informed about waether helm on traditional boats with fine exits. I am trying to reasearch the subject of weather helm on traditional shalow draft long keel designs.

    My boat is a Bohusjolle (SW Sweden) built in 2006 in Estonia to an 1880 very common traditional design with a couple of British additions such as a foredeck. Her frames are of oak and planking probably larch or pitch pine (translation issues). She is approx 16'6" hull length with another 4" of bowsprit. Her beam is 6'6" and is almond shaped. she has a wine glass transom with a substantial rudder. She draws 18" of water and has a long 12" draft keel shod with 100kg of lead. She is probably the better side of 450kg overall.

    In sailing terms I have never felt so comfortable, the sails are generous and she does move exceedingly well, except for one aspect. The helm is beutifully neutral on all points aft of abeam. Then the higher to wind we point the heavier the helm and it does go beyond 4 degrees. In an F5 tight to wind and running with just the inner jib and main it gets a bit wearing and anoying seeing all that speed lost with the rudder swirl.

    I hope this is enough to open the batting, can any one help?
     
  2. Oldlugger
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    Oldlugger Junior Member

    Just spotted a mistake the bowsprit is approx 4 feet in length not 4 inches.
    Best Regards Oldlugger
     
  3. TeddyDiver
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    TeddyDiver Gollywobbler

    Have you tried how it sails in the same conditions with foresail instead?
     
  4. Tcubed
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    Tcubed Boat Designer

    Just the staysail will increase the weather helm . Try instead when you must reduce canvas to first take a reef in the mainsail, and leave the jib.

    Also 4 degrees is a good amount . If you said 10 degrees i would understand wanting to reduce it a bit but for degrees is very good for making the underwater shape more efficient to windward.

    Another thing you have not mentioned but is worth noting is if it is loose footed it is very critical to get the lead on the mainsheet just right.
     
  5. Oldlugger
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    Oldlugger Junior Member

    Interesting comments and thanks.

    The main has a boom with kicker, the main sheet runs off a horse on the transom then leads in to be a center main. The main foot is loose, only attached at the clew, I have 8:1 adjustement.

    The luff is laced to the mast and has a cunningham of sorts to get a good edge to the luff. The mast is a telegraph pole with zero flex to talk about. It is approx perpendicular to the keel/waterline.

    The sprit runs of a ring up to the peak and is adjustable. I can change the main shape depending on wind to which it is very sencitive.

    Running before and through to a broad reach I fly the Staysail and Jib. To get closer to the wind I furl the jib, this gives me maybe 5 to 7 degrees advantage when tacking. I have also added advantage to the staysail and jib haliard to get a decent tention, this gave a further couple of degrees advantage.

    In heavy wind I have always furlled the jib this has a very pronounced effect. After thatI tend to spill wind from primarily the main or redistribute the crew as in hang them over the weather rail, when that fails its time to get back to the mooring because its blowing old boots and dogs off leads.

    I have not tried to furl the Staysail and fly the jib.

    In responce to the amount of weather helm I have estimated approx 8 degrees average. This will vary on the position of the crew for and aft and obviously angle of heal.

    This is the point that gets interesting, theory sugests that crew weight should be forward but practice suggest the weight should be toward the stern.

    I hope that this can stimulate a few comments.

    All the best
    Old Lugger
    (my other boat is a 19' Northumbrian Coble)
     
  6. Tcubed
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    Tcubed Boat Designer

    Weight aft will reduce weather helm since you're dealing with a low aspect keel and rig. The aftward shift in lateral resistance will vastly overcome any aftward shift in the center of effort.

    I do not understand why you take the jib down to sail higher. It sounds to me you have something not quite right with the jib. Almost always this will be because the jib is too full, and the jib could be too full because of insufficient halyard tension if it is set flying. Increasing the jib halyard purchase is definitely a good thing, as you seem to have done. However if it has a poor cut then you will need to recut the luff to flatten it.

    I found in my cutter that an excellent sail combination for heavy airs was to set the storm jib , no staysail and reefed main. The storm jib was a blade jib cut nicely flat and strong with the draft close to the luff. Having the sails spread out longitudinally made it easier to get the boat to self steer steadily.

    Another thing that wil affect weather helm is heel angle. Typically , shallow beamy boats will develop weather helm with increasing heel , especially if it is a double-ender.
     
  7. Tcubed
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    Tcubed Boat Designer

    You do have a boom so mainsheet lead will only affect twist, not camber.

    Since you have loose footed with a boom you can tighten the outhaul to flatten the mainsail and this will also go some ways to reducing weather helm.
     
  8. alan white
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    alan white Senior Member

    Maybe experiment with stays'l lead---- try more forward position. It could be too flat. The main could be too full.
    Weight in the stern will possibly round you up if the buttock sections are squarish and the stern wide. Is this a wide-sterned boat?
     
  9. Oldlugger
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    Oldlugger Junior Member

    Dear Members
    My apologies for not responding earlier but some parts of the world seam not permit access to this site.

    Many thanks for all the replies. The reason I furl the jib in preference to the staysail is a belief that it would take the centre of effort forward thus increase weather helm. It would seam to be so when phrased in the standard calculations. So I am a bit confused.

    I have attached a pic of Jessy B on a reach and the tiller is neutral, you will notice that there is insufficient tension on the forestay and on the jib luff, this was rectified by putting mechanical advantage on the halyards as previously mentioned. The staysail now has a Wycombe Martin furling system.

    The other amendment was the repositioning of the sheet eyes, both are now on travellers to permit adjustment, You will notice the jib is hooking. The cut of both forward sails is thought to be fair but the main a little too flat. When max outhaul on the foot is added an adjusting the peak not a wrinkle can be seen nor any shape to talk about. Modest travel in both foot and peak generates a reasonable shape for gentle airs but by no means are they full.

    She sails generally quite flat as I have a suficient mass to be regarded as helm & crew. But when the wind is up and two crew are getting damp total crew weight is getting on for 45 stone... I am concidering an extra pair of stays as pressing on seam to have bent a couple of bits. Total sail area is approx 15 squ metres and I am about to add a topsail which will give me an extra 3. The topsail was on the original line drawing and intended for use in sub F3 winds.

    look forward to more comment
    BR Oldlugger
     

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  10. alan white
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    alan white Senior Member

    Taking the center of effort forward would decrease weather helm. As weather helm is a strong tendancy for the boat to turn into the wind, adding sail area forward adds leverage to swing the boat off the wind.
    Even though the CE is ahead of the CLR on paper, in practice, the CLR is ahead of the CE, and moreso when the boat begins to heel.
    All mains'ls move their CE ahead when reefed, which is good, because that's exactly whet's needed.
    A well-reefed down cutter, admittedly, traditionally carries the stays'l after the jib's been furled, but this has more to do with sailhandling ease than anything else, and anyway its not a hard and fast rule.
    Try carrying the jib to the last and see what happens.
     
  11. Oldlugger
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    Oldlugger Junior Member

    Ahh that would be the rather obvious thing that I did not see then, oh dear what a chump. I will however attempt to defend my idiocy with probably another misconception.

    Surley going to windward the forsail would give better flow to the back of the main? he said weakly?
     
  12. alan white
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    alan white Senior Member

    In reefed conditions, balance is far more important, I think. Going to windward in light air however, overlap is very effective, and setting a genoa would be even more effective than two headsails.
    You can't beat the cutter reaching with the two headsails in any case. That's where they really shine.
     
  13. Oldlugger
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    Oldlugger Junior Member

    Hi Alan and thank you for all the help and info. I will look at a genoa next year, but for now I will tweak what I've got.
    Once again many thanks.
     
  14. PAR
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    PAR Yacht Designer/Builder

    I don't think it's a lead issue and I believe I'm the one who you mentioned in your first post.

    A quick look at your aft quarters could easily explain why your boat has a nastily tendency to round. Have you any images of the boat, out of the water, from a 3/4's aft angle, preferably close to the LWL. Any images of the stern quarters will help.

    I say this because it's very difficult to design a double ender properly, with the common mistake being found in the sweep of the buttocks. This is especially true of boats with short overhangs aft. From a design point of view, it's very difficult to keep the run sweet and still tuck everything into the stern post of a double ender.

    The net result of a "quick" or "tucked up" run is a fairly hard turn upwards of the buttocks at the LWL usually results. This "fullness can bury the bow (which has to be shaped to accept the limitations and annoyances of the stern) and if much heel is on, a witch to steer (if you can at all) Norwegian pilot boats and other craft with short, double ended over hangs and bulbous butts are notorious for this trait, if not carefully designed. Have you any photos?
     

  15. Oldlugger
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    Oldlugger Junior Member

    Hi Par
    Attached are the best views I have. She is not a double ender but close. Also attached is the line drawing that was the basis of the design from approx 1880.
    best regards
    Oldlugger
     

    Attached Files:

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