Gunwhale rules

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This topic contains 4 replies, has 2 voices, and was last updated by  Tim Thornton 6 years, 4 months ago.

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  • #51538

    Tim Thornton
    Participant

    What must be the slowest Mk IV conversion is edging towards completion!

    A question on the rules for the gunwhale and rubbing strake – I think I have got it right but confirmation before gluing would be nice!

    The relevant rules seem to be D.6.2 and D.8.2 (the deck overhang and gunwale rubbing strake dimensions). None of the variations of Fig 2 apply as only 2E and 2F apply to the Mk IV, and neither of these have anything relevant.

    My understanding is that:
    – the deck overhang (i.e. all wood outside of the hull skin, including the rubbing strake) has a max width of 50mm (presumably measured at right angles to the boat’s centreline – I cannot see this stated) but no minimum and no restrictions on tapering, except for those implied by the rubbing strake rules
    – the rubbing strake has to run unbroken for the length of the boat
    – the width of the rubbing strake must be within 10-50mm and constant +/- 5mm except for within 1000mm of each end where it can taper. So, for example, it could be 40-50mm wide in the middle and then taper to 10mm at the ends
    – the depth of the rubbing strake seems to be just restricted in D.8.2, so can be 20 – 30mm, and constant with no tolerance at all in the middle of the boat (not even 1mm!) and tapered towards the ends
    – the plane in which the width and depth is taken is not specified. I guess it is horizontal and vertical, square to the centreline. This is important in case the gunwhale is angled, and so the rubbing strake is not being glued to a vertical surface.

    Does this make sense?
    Tim

    #53378

    Tony Thresher
    Participant

    Hi Tim,

    I think you have it all correct. The widths are measured from the sheerline (intersection of the outside of the hull skin projected to the top of the deck). Deciding where this point is is tricky on a Firefly as the outside of the skin is not flat. By the time the skin reaches just under the gunwale it is pretty much vertical but the angle does vary at different poits along the hull hence effecting where the sheerline is.

    If I’m guessing correctly your questions revolve round whether you can creat an angled gunwale and then cap it as per Merlins, N12s, Solos. This is what I considered when I first did a couple of MK4 conversions and concluded that the drawings didn’t show this construction so best not. However I’ve subsequently seen another builder construct this kind of gunwale and nobody seems to mind. Consequently the Rondar composite I launched yesterday has a gunwale capping that is glued onto the flange used for bonding the deck to the hull on the glass boat which creates an anled gunwale like the Rondar and what I think you are considering. I certainly will construct any future gunwales on Firefly conversions/redecks/composites in this way.

    As usual I’m sure if you work within the numbers and creat something that looks like a Firefly you’ll be fine. In other words no super wide flared gunwales in the middle.

    Tony

    #53379

    Tim Thornton
    Participant

    Tony,
    Thanks for the reply. Yes, I’m planning to angle the gunwhale in the cockpit area, then bring it to be more slab sided towards the bow. I don’t see a problem with this in the rules, it is more making sure of the plane the dimensions are taken in.
    Tim

    #53380

    Tony Thresher
    Participant

    Tim,

    I would read the depth as having to be between 20mm and 30mm but not constant. I doubt if there is a firefly on the water that complies if you read it the way you suggest. 25mm +/- 5mm constant would be clearer.

    Tony

    #53381

    Tim Thornton
    Participant

    I agree that that is a more commonsense reading, but D.8.2 says it can only taper within 1000mm of the ends, and there is no rule equivalent to D.6.2.b giving a tolerance on the vertical dimension.
    Probably a good candidate for a rule change at the next AGM before someone insists that the rules are applied as they are written!

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