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  1. #11
    Join Date
    Feb 2005
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    225

    Default Re: Rounding up under pressure

    Same goes for you, Nigel.Try bringing that (extremely) far aft mainsheet attachment forward. Its easy to do. To clear your tiller, try a bridle and a much shorter tackle.
    Pete

  2. #12
    Guest

    Default I know the idea you put ...

    With our sheets on the horse as is .. the boom is effectively pulled in at the stern end and undercuts the sail ... causing a rounding moment ... bring the sheet more forward then sheets the boom straighter ...

    My main would make it a serious structural problem to rig sheets futher forward ... worth a look ... but attachment would need serious underpinning ....

  3. #13
    Join Date
    May 2001
    Posts
    29,103

    Default Re: Twin rudders ....

    I disagree. While luffing is the normal practice in a dinghy, a safer option for a cruiser if overpressed is to bear away onto a broad reach. It brings the boat upright and restores control plus it reduces the apparent wind.

    Rounding up runs the risk of losing steerage way and control.
    One hull good, two hulls better.

  4. #14
    Guest

    Default Snowleopard ... if I was in UK ...

    I would invite you on board to demo that ..... I think you would change your mind - for my boat - after you pick yourself up out of the water !!

    I understand what you are saying .... but in fact the rounding up of a boat is an extension really of the weather helm aspect ... an in-built safety aspect of a boat ...

    Put a less experienced person on the helm and press the boat ... I would feel much happier with the boat taking over and rounding up than they trying to bear away ...

    We all know that as a boat rounds up to the wind that the hull digs in on its lee-side ... if you bear away lee-side will lift ... but unless you are careful to adjust all sheets as you do it the wind now is attacking the sails at more direct angle and PUSHING you over rather than sailing you over ....

    I think I'll stick with rounding up when pushed to extreme ....

    As to the downwind bit and broaching ......... thats where I like the downwind tacking idea to get around that ....

  5. #15
    aitchw's Avatar
    aitchw is offline Registered User
    Location : West Yorkshire, UK
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    Feb 2002
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    Default Re: Rounding up under pressure

    Pete, that's something (again) I have never considered and I can see the point. Problem is in small boat there is precious little cockpit space and to bring my mainsheet attachment forward would create an unwanted obstacle in that already restricted space. The mainsheet is attached to a traveller right on the aft edge of the cockpit at present.

    As to the 'diatribe' I will happily read everything you want to post. It's always helpful to widen the scope of the way I think.

    I don't want to paint a picture of a bad mannered little tub, she most certainly isn't. Idiosyncratic, yes. What I'm trying to reach is a point where she is as well balanced as I can make her without losing the essential safety aspects of her behaviour. She is a small boat with all the limitations that imposes but I want to get her to the point where she will handle F3-4 without a battle. She doesn't carry a lot of cloth, current jib+main is only about 100sq.ft so I don't reckon she should be overpowered in a low F4.

  6. #16
    Guest

    Default Re: Rounding up under pressure

    I thought at first you were joking about moving the mainsheet in, but now I'm not so sure. But just in case some poor soul reads and decides to start moving his mainsheet - moving the mainsheet fore and aft makes no difference to the turning moment on the stern. If you move the mainsheet from the end of the boom to closer to the mast then you are just increasing the strain on the main sheet, a greater force closer to the mast having the same turning moment as a lesser force further out.

    What matters is the centre of effort of the sails (in relation to the centre of lateral resistance of the hull when heeled).

  7. #17
    aitchw's Avatar
    aitchw is offline Registered User
    Location : West Yorkshire, UK
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    Feb 2002
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    Default Re: Snowleopard ... if I was in UK ...

    The other point about bearing away under these circs is, at least momentarily, you need more bite from the rudder at just the point where it is likely to give up anyway. Could take the matter out of your hands. If you did have more to go at you would definitely need to ease the main as you fall of the wind. Not to do so would be pretty risky.

  8. #18
    aitchw's Avatar
    aitchw is offline Registered User
    Location : West Yorkshire, UK
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    Feb 2002
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    Default Re: Pity we are talking about older designs and NOT AWB\'s ...

    I see you have probably about the equivalent blade area I do relative to LWL though close to 2:1 aspect and not much more bilge keel area, so I can also see the possible similarities in handling. My rudder plate is slightly less than 1:1 (don't laugh!).

  9. #19
    Slow_boat's Avatar
    Slow_boat is offline Registered User
    Location : My own cosy little world where nice things happen and life is beautiful all the time
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    Sep 2005
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    14,782

    Default Re: Rounding up under pressure

    I've noticed when sailing AWB on charter that they are much more stable heel less and are no slower close hauled in a good breeze under foresail alone than reefed main and fore.
    Not tried it on my little tub and I know it shouldn't be so in theory but there it is....

  10. #20
    Join Date
    Feb 2005
    Posts
    225

    Default Re: Rounding up under pressure

    Simon cr.- You misunderstand - its where the mainsheet is attached to the boat hull thats important. Whilst you are absolutely correct in pointing out that its the centre of effort of the sails that is crucial, this point has already been covered by referring to mast position and the theory of moving the mast forward and with it the centre of effort of the sails, relative to the centre of lateral resistance of the hull.
    Also, the sails have NO centre of effort until they are filled with wind AND hauled in and attached to the hull. Its where this attachment is, relative again to the centre of lateral resistance of the hull, and the actual physical lateral resistance relative to the point of sail,and the speed through the water of the hull relative to the wind pressure, which is the nub of the thing.Hence a boat moving slowly hit by a gust will round up violently,yet the same boat, moving at hull speed, will react less violently to a proportionaly larger gust. This becomes much more complicated now, involving a host of variable factors like hull form ,weight,wetted area, hull shape when heeled etc,etc.
    The only thing I can say to you doubters, is try it. Those of you with mainsheet travellers across the cockpit who may wish to `reverse prove` this theory by moving your attachment point BACKWARDS by making up a strop across your aft cleats or whatever and experimenting, don`t do it in strong winds, and make sure those on board are hanging on tight.Even moving it aft a couple of feet can result in violent rounding up in quite moderate conditions.
    Your point about increasing loads is taken,but they are taken by the boom more than the mainsheet. A foot or so forward of the end won`t make much difference.
    Another diatribe.
    Cheers,
    Pete

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