Forward mast rake and friction

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  • 22 Nov 2023 00:52
    Reply # 13282393 on 13282091
    Anonymous wrote:

    Why I avoid forward mast rake where I can

    All fore-and-aft sails have their centre of gravity, CG, moved out to the side (or aft) with respect to the mast top, they being gaff, lugs or junk sails.
    For a junksail this means that the sail constantly must be held from falling forward when raising and lowering it. This means that lines like batten parrels or standing luff parrels will have to rub on the mast as the sail goes up and down, and this adds friction. The angle between a line from the sail’s CG to the mast top could be called the CG offset line, and its angle to a vertical line would then be the CG offset angle. This angle is critical to how much friction there is between the sail and the mast, both as the sail goes up, and when it is coming down. The lower the aspect ratio of the sail, and the lower the sail’s mast balance is, the higher goes this CG offset angle, and the friction with it.

    On the sail I use on my Ingeborg, this offset angle is about 21°. On the diagram below, I have swung the lower end of the mast 4° aft around the present mast top (and the sail with it). This increases that CG offset angle to about 25°.

    The sail of my Ingeborg has tolerably low friction in it when hoisting and lowering it. I can mostly crash-dump it without any need for hauling it down. In a pinch, I give the shown THP a light tug, and down comes the rest.

    However, if I had rigged the sail with the shown 4° mast rake, that THP certainly would have been needed more often, and hoisting the sail would have been harder. Therefore, minimising friction is my main reason for sticking with a plumb mast.

    Even so, sometimes there are good reasons for raking the mast forward. On a foremast on a schooner, for instance, or if the deck layout or interior dictates the mast rake. Annie Hill has another argument for it. She sails up and down the east coast of NZ (North Island). There she often experiences a combination of light winds and old swell rolling in from the Pacific. She finds the mast’s forward rake helpful in taming the sail in these conditions.

    Well and fine, I respect such good reasons. However, I will always aim for a plumb mast as long as I see no real need for rigging with forward (or aft) mast rake.

    Cheers, Arne

    (..PS: And don’t come and tell me that a forward-raking mast looks smarter or saltier...)

    (Full size diagram at Arne's sketches Section 7...)


    Well Arne, I beg to differ. I always put forward rake in my designs as I've mentioned to you elsewhere. I find it helps to stabilise the sail when off the wind and of course it can be used to get the CE where you need it when it's no possible to get it there by other means. 

    I've used everything from 0° forward rake to 10° of it and I've experienced no problems with any of my sails coming down.

    Last modified: 22 Nov 2023 07:34 | Anonymous member
  • 21 Nov 2023 17:05
    Reply # 13282171 on 13282145
    Anonymous member (Administrator)
    Anonymous wrote:

    Always good to listen to your experience.

    in the first sentence, do you mean ‘aft’ rather than ‘to the side’.

    Ah, I see. Aft is probably best although that depends if the sail is squared out or sheeted in. Now I have corrected the term "fore and aft" to "fore-and-aft" sail...

    Arne
    Last modified: 21 Nov 2023 19:32 | Anonymous member (Administrator)
  • 21 Nov 2023 16:27
    Reply # 13282145 on 13282091

    Always good to listen to your experience.

    in the first sentence, do you mean ‘aft’ rather than ‘to the side’.

  • 21 Nov 2023 14:37
    Message # 13282091
    Anonymous member (Administrator)

    Why I avoid forward mast rake where I can

    All fore-and-aft sails have their centre of gravity, CG, moved out to the side (or aft) with respect to the mast top, they being gaff, lugs or junk sails.
    For a junksail this means that the sail constantly must be held from falling forward when raising and lowering it. This means that lines like batten parrels or standing luff parrels will have to rub on the mast as the sail goes up and down, and this adds friction. The angle between a line from the sail’s CG to the mast top could be called the CG offset line, and its angle to a vertical line would then be the CG offset angle. This angle is critical to how much friction there is between the sail and the mast, both as the sail goes up, and when it is coming down. The lower the aspect ratio of the sail, and the lower the sail’s mast balance is, the higher goes this CG offset angle, and the friction with it.

    On the sail I use on my Ingeborg, this offset angle is about 21°. On the diagram below, I have swung the lower end of the mast 4° aft around the present mast top (and the sail with it). This increases that CG offset angle to about 25°.

    The sail of my Ingeborg has tolerably low friction in it when hoisting and lowering it. I can mostly crash-dump it without any need for hauling it down. In a pinch, I give the shown THP a light tug, and down comes the rest.

    However, if I had rigged the sail with the shown 4° mast rake, that THP certainly would have been needed more often, and hoisting the sail would have been harder. Therefore, minimising friction is my main reason for sticking with a plumb mast.

    Even so, sometimes there are good reasons for raking the mast forward. On a foremast on a schooner, for instance, or if the deck layout or interior dictates the mast rake. Annie Hill has another argument for it. She sails up and down the east coast of NZ (North Island). There she often experiences a combination of light winds and old swell rolling in from the Pacific. She finds the mast’s forward rake helpful in taming the sail in these conditions.

    Well and fine, I respect such good reasons. However, I will always aim for a plumb mast as long as I see no real need for rigging with forward (or aft) mast rake.

    Cheers, Arne

    (..PS: And don’t come and tell me that a forward-raking mast looks smarter or saltier...)

    (Full size diagram at Arne's sketches Section 7...)

    Last modified: 21 Nov 2023 19:28 | Anonymous member (Administrator)
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