Latest News: Forums Technical Pivot Pin

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  • #7247
    Swiebertje
    Participant

    deleted

    #7249
    Anonymous
    Inactive

    Mato,

    You are quite correct in that applying rig tension alone will not inherently cause the mast to pre-bend, at least assuming that your spreaders are free to rotate fore and aft.

    If you have adjustable spreaders then you can use these to translate the rig tension into pre-bend if you wish. If you adjust them so that the shrouds are being deflected aft then rig tension will cause the shrouds to straighten forcing the hounds forward and bending the mast, depowering the rig and flattening the sail.

    Or you can use chocks behind the mast if you want to get it to bend without applying kicker (eg for very light winds when you need the sails flat). As the wind strengthens you then switch to having chocks in front of the mast to prevent it bending, then in stronger winds remove them all together so that the rig can depower “on demand”, ie by applying kicker.

    Remember to use the minimum allowable mast pin size (6mm from memory) which makes it a whole lot easier to get the settings you want without it becoming tight.

    Another idea I had – though I’m not sure of the legality of this – was to elongate the pin hole horizontally either in the mast or in the tabernacle (or even in both) to provide the required range of fore and aft movement. Has anyone done this?

    #7252
    matoi
    Member

    John,

    The theory about spreaders makes sense. But I did check spreader length and deflection against the table on Selden/Proctor web site (http://www.seldenmast.co.uk/dinghy/tuning.asp?Class=Wayfarer) and everything seemed to be installed just in the middle of extremes. (I didn’t use the table from the WBook because I faintly remembered hearing somewhere that it doesn’t apply to World version, though I must admit not actually comparing the Selden and WBook data – should do it tonight).
    But, looked from side of the boat, the shrouds on my boat seem to run almost in a perfectly straight line from the hounds to the hull (http://picasaweb.google.com/matopics/VarietyOfConditions/photo#5218536600164006546), so I still don’t see how they can force mast to bend…

    Perhaps I am doing something wrong / making an error when taking a measurement or something…. It would be best if someone more experienced could check what I’m doing, hopefully there will be such an opportunity next week.

    Best regards to all,

    Mato

    #7254
    Colin Parkstone
    Participant

    Matoi,
    Are your putting the pin in the mast step in before, or after the tension is put on. If before it may not be allowing the foot to slide back in the track.

    Is that pin to far forward to start with, if so, even when the tension is put on the heel is to far forward and is resisting the pre bend.

    The way to set up the pre bend is to do all other things first,spreaders,free pin and pre bend and then fix the heel pin to the back of the mast heel.

    You say that the shrouds are in a stright line with tention on, that suggests
    that the spreaders are to far forward and have no more forward movement left,try moving them back and fixing them if not already then the mast should bend forwards.

    CP 😀

    #7255
    matoi
    Member

    Dear Colin,

    When this ‘prebend business’ first became strange to me, I checked the spreaders, but I never moved the track pin from the position in which it was installed when the boat came from builder, and I admit never checking it’s position via tape measuring the rake. Perhaps I should have… I tend to trust people. Thanks for pointing this out.

    Best wishes,

    Mato

    #7257

    Mato

    I have a world and at the Ullswater Gathering a couple of weeks ago John (the very kind and helpful cruising secretary) kindly looked at the setup. It became apparent that the setup put on by Porter’s when I bought the boat was not optimised. We tweaked the spreaders (length and angle), altered the pin locations on the shroud plates (at the bottom) and also had to adjust the pin in the mast foot track. It’s final position was the aft hole. When I now step the mast I have to remove the pivot pin to get the mast foot back the final bit (as Colin suggests) but then the pin goes back in and sits freely. As a result I get a mast bend like I never had before. I suggest you contact John for the measurements as (as you have suggested) the world measurements differ slightly from those in the W Book. The chocks provide a limit to the bend.

    She sailed much better afterwards. Good luck.

    #7258
    Colin Parkstone
    Participant

    Mato,

    It is a minefield all this rigging and prebend but keep on trying and it will all come to light.

    So maybe set the mast up with the pivot pin out the way, then the mast heel pin in behind the heel and then see if the pin will go through the mast after that.

    CP 😕

    #7259
    Dave8181
    Member

    A 6mm pivot pin with holes for retaining rings at each end, can be made up by local marine stainless steel suppliers.

    The tuning guide settings for the spreaders are not an exact guide. Generally the guides have been written with wooden boats in mind, whereas GRP boats have slightly different shroud positions.

    It is the rake and prebend measurements that are important, and the spreader length and angle can be adjusted from the starting point in the guide, to achieve these settings. Looking along the tensioned shroud, one can see which way it deflects at the spreader end, and so get an indication of what forces/prebend the shroud is applying to the mast. Raking the spreaders back will increase prebend.

    After getting the prebend and rake correct by adjusting shroud length and the spreaders, also with the pivot pin loose, chocks are fitted to limit further lower mast bend such as when the kicker is tightened (not to create prebend). The chocks should only be used in front of the mast.

    The mast track rear pin can then be positioned close behind the mast foot, and small metal shims added to fill any small gap remaining between the rear pin and the back of the mast foot, so that the mast will be located in a consistent position, with the pivot pin loose, each time rig tension is applied.

    Dave8181

    #7262
    matoi
    Member

    Guys,

    I think the mist around my problem is being dissolved.

    Thank you very much.

    Best regards,

    Mato

    #7271
    Swiebertje
    Participant

    @Dave8181 wrote:

    A 6mm pivot pin with holes for retaining rings at each end, can be made up by local marine stainless steel suppliers.

    A much cheaper solution, that has held well for years on my old boat, is a simple galvanized 6 mm bolt and a wing nut. True, they start to rust after a year or two but they are so cheap that I can only buy them four in a package. You can buy twenty of those bolts and nuts against one Wayfarer standard stainless steel pin. Hence the SS pin gets cheaper after 40 years of use. 😉

    #7272
    Anonymous
    Inactive

    @Swiebertje wrote:

    @Dave8181 wrote:

    A 6mm pivot pin with holes for retaining rings at each end, can be made up by local marine stainless steel suppliers.

    A much cheaper solution, that has held well for years on my old boat, is a simple galvanized 6 mm bolt and a wing nut. True, they start to rust after a year or two but they are so cheap that I can only buy them four in a package. You can buy twenty of those bolts and nuts against one Wayfarer standard stainless steel pin. Hence the SS pin gets cheaper after 40 years of use. 😉

    Following this train of thought, why not go the whole hog and just use a stainless bolt.

    Less than 19 pence each here…

    Screwfix

Viewing 11 posts - 16 through 26 (of 26 total)
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