moving mono mast forward /weather helm

Discussion in 'Boat Design' started by gramos, Dec 12, 2007.

  1. gramos
    Joined: Nov 2007
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    Location: greece

    gramos Junior Member

    a friend has a 38 timber yacht with a fairly tall cutter rig and is talking about shifting the mast forward by 4/500 mm to try to counteract the strong weather helm . the boat is quite tender even with a tired main and genoa. is he looking into the right area to resolve this ?
     
  2. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    First determine the actual rudder deflection. This can be averaged over several close hauled runs. If you have 5 degrees or more in moderate wind strengths, then you may have weather helm.

    The next thing to do is decrease the amount of mast rake. Possibly a different headsail(s) combination can help.

    If these things have been tried, then it's time to look at adding lateral area aft (skeg, rudder, keel, etc.) or possibly moving the whole rig.

    Moving the whole rig is often a quite involved job. A scale drawing of the current sail plan is necessary as well as a scale drawing of the underwater profile.

    With these in hand find the current CE and CLP, noting them on the LWL. Calculate the amount of CE lead and make a decision about how much you what this to change. On your boat you'll probably have 10 to 13 degrees of lead, maybe less, since you're helm is heavy.

    Now the fun part begins, you have to guess (educated) where you want the lead to be. There's no set rules or reliably predictable guidelines you can resort to, so I'm not kidding when I say guess. This isn't a task to be taken lightly.

    Most all rigs can have lee or weather helm issues "turned" out by a good rigger or experienced skipper.

    90% of all sailboats have poorly tuned rigs, fortunately the designs are so forgiving, that they sail reasonably well anyway. A well tuned rig, against a fleet of identically sailed boats, means you'll be at the front of the herd, not mired down in the pack.

    Find a sailboat rigger or seasoned racing skipper and have them tune the rig.
     
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  3. tom28571
    Joined: Dec 2001
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    Location: Oriental, NC

    tom28571 Senior Member

    The statement that the boat is quite tender is a clue that moving the mast may not be the answer to weather helm. Most books blame weather helm on lack of balance of CLR and CE but that is only part of the story and often not even the main part. In a tender boat, the driving force is well to leeward and the underwater reacting force is to windward. This makes a couple that is trying to turn the boat to windward or, in other words, weather helm.

    This heeled sail/keel effect is often the major contributer to excessive weather helm and no reasonable amount of mast shifting is going to cure it. Less sail and or more righting moment may be the only cure.

    Tired or blown out sails are also a contributer to weather helm.
     
  4. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Tom is correct. Most complaints of weather helm aren't actually weather helm, but usually a combination of issues.

    Get a well seasoned pro aboard for a sail. They'll know what's going on in just a few minutes.
     

  5. BOATMIK
    Joined: Nov 2004
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    Location: Adelaide, South Australia

    BOATMIK Deeply flawed human being

    Exactly right PAR,

    Over the years almost every example I've run across with a boat "failing to perform" whether it was a case of helm or just a lack of speed or pointing has been able to be resolved by a few basic changes during a test sail. Or even on examination of the boat or photos of it sailing.

    Moving masts is complicated and expensive - and may not be resolving the actual problem.

    Best wishes
    Michael Storer
     
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