Latest News: Forums Technical Mk2 SD Thwart

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  • #4384
    revoli
    Member

    Woe is me. Such a beautiful day to sail and I am still in pieces in the workshop. Still if a jobs worth doing and all that. Now, when you wonderful helpfully people return from your days sailing could you turn your mind to this query. My thwart has some cracks about 6 inches long going across the boat. On inspection these appear to be stress cracks possibly caused by how the thwart is attached to the centreboard housing (??my term). What I do not know is is this the original design or has someone carried out a repair that has introduced new stress points. Picture to be attached. My thwart is attached to the centreboard housing by two screws along the front edge and by fibreglass patch applied underneath on both sides of thwart. The cracks run across the boat roughly along the edge of the fibreglass pAtch. My options are to reinforce the thwart to centreboard housing to provide a rigid connection beneath the cracks. I wonder though if the original design was to leave this free moving and effectively have the thwart just supported at it’s sides? Doesn’t seem likely but I need to check and have no access to another mk2 to compare. Can someone look under their thwart and tell me if it is connected as mine?

    #10537
    Dave Barker
    Keymaster

    I’ll have a look under mine next time I have a chance, but I would say without doubt that the thwart would be bonded to the case. I say this because without it the forces imparted by the centreboard via the case would cause much more serious cracking lower down, where the case joins the floor of the boat. For example, imagine a heavy guy standing on the centreboard to right the boat after a capsize.

    Does it look as though there have been fittings (toestraps, kicker cleats etc) attached to (or near) the edges of the thwart? Even the weight of someone standing near the edges of the thwart might cause cracking? Having said that, it doesn’t look the most professional grp job ever…

    #10553
    revoli
    Member

    Dave – did you manage to take a look?

    #10554
    Dave Barker
    Keymaster

    I’ll go and look in the morning.

    Probably…

    #10555
    Dave Barker
    Keymaster

    Sometimes I even remember to do stuff! Here are a couple of photos, showing the (tatty) undersides of the thwart on ‘Cockle‘ at the junction with the centreboard case. The thwart is bonded to the c/b case, and there seems nothing to suggest that it hasn’t always been like that.

    (I think the rusty metal is the remains of a bracket that someone fitted years ago to hold a pump – not a good place for it if you’re sleeping in the boat).

    #10556
    revoli
    Member

    Many thanks, that helps alot. I now know how I need to carry out reinforcements. As she is currently upside down in the workshop sitting on bags of peat there are going to be plenty of expletives from the underside of my wayfarer…

    #10557
    admin
    Member

    Do clean off the old white paint and try to get a”key” into the GRP, probably best done mechanically, don’t use chemical stripper.

    Do use epoxy resin and woven cloth (not polyester resin and Chopped Strand Mat).

    If you laminate a further layer or two of glass under the cracks you will strengthen the thwart, but if you can introduce a spacer (eg foam strips) so you end up with a sandwich, it will incrrease the strength many-fold. In fact why not laminate a piece of wood under there so you can screw stuff onto it (as in Dave’s boat)? I have some cheek blocks under there to divert controls to the helm.

    Mike

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