Hinged mast with sliding outer sleeve

  • 25 May 2018 08:39
    Reply # 6260871 on 6191276

    3mm gap all round is certainly excessive; I haven't seen one that slack. Your trial with the guttering seems the right approach to me, Kurt. If there is room for two, protruding above the sleeve a little so as to help with fairing the step, that ought to fix the problems as far as they can be fixed, but I think I'm always going to prefer a firmly clamped tabernacle arrangement.

    Last modified: 25 May 2018 08:42 | David
  • 25 May 2018 07:59
    Reply # 6260845 on 6191276

    Timely topic for me and minim! Thanks!

    She's a 21' Coromandel with a hinged and sleeved alloy mast, such as many Coromandels and other small junks have.

    I first raised the mast only a few days ago. No problem handling the 21' tapered mast, hinge-pin and sleeve solo, afloat in mild conditions. Tape to retain the sleeve, vigilance to not lose the pin...

    When the River Deben got choppy later, noises from within the loose (gap of 3mm all around) sleeve told me this thing will grind and knock itself to bits eventually, and sailing will be stressful.

    The former owner used little wooden wedges at the sleeve-top. I put a set in, but the hinge itelf kept knocking and grinding, gyrating in the gap at mid-sleeve. Then the wedges started blowing away. A plastic half-pipe (house gutter) filled the gap better, and spread the point-of-contact load, somewhat. I'm going to pursue this approach.

    I'll try to fit a pair of half-pipes, to fill the radial gap the whole length of the sleeve, which I must ensure remains able to slide. 

    There's a conical alloy fairing-piece to help battens & parrels pass the unfortunate step. The fit of the sleeve on the collar at its lower end is pretty good.

    The glass-epoxy bulking-up method seems another good option. Maybe later.

    If absolutely no wobble, slight possibility no slide...

    (photos: experiment at top of sleeve; bottom of sleeve at collar; mast stub & style of hinge)

    Cheers, Kurt



    Last modified: 25 May 2018 08:03 | Anonymous member
  • 25 May 2018 06:32
    Reply # 6260725 on 6258718
    David Webb wrote:

     David, I suggested a couple of tangs on the bottom of the sliding section that the topping lifts could be attached to in order to lift the sliding sleeve, this would also hold the sleeve in place while the mast was raised and lowered. Do you think that would solve the problem you talked about in your last post? Also one advantage of the sliding sleeve is that it allows the rig to be lowered below the hinge. This means that nothing has to be loosened or changed on the parrels etc in order to lower the mast. 

    I'd be reluctant to add anything to the outside of the sleeve, that would snag the batten parrels. They need to slide off the sleeve readily in both directions. The sleeve needs to be held up until you're ready to lower it over the hinge, and held up while you lower the mast: it's a simple problem, requiring a simple solution. How about drilling a hole in the upper part of the hinge that would accept a 5 or 6mm pin?
    Last modified: 25 May 2018 08:26 | David
  • 24 May 2018 10:15
    Reply # 6258718 on 6191276

    Hi Graham,

    the fiberglass looks good. I think that short sections of a PVC drain pipe epoxied to the mast may work on 100mm and 150mm OD aluminium mast sections. The sliding section sizes I have come across seem to give about 10 to 12mm clearance on the mast sections so the 3 to 5 mm wall thickness of the PVC pipe would leave 1 to 2 mm clearance to allow it to slide. PVC has a certain amount of natural lubricity so should help the parts to slide.

     David, I suggested a couple of tangs on the bottom of the sliding section that the topping lifts could be attached to in order to lift the sliding sleeve, this would also hold the sleeve in place while the mast was raised and lowered. Do you think that would solve the problem you talked about in your last post? Also one advantage of the sliding sleeve is that it allows the rig to be lowered below the hinge. This means that nothing has to be loosened or changed on the parrels etc in order to lower the mast. This is particularly useful with an Aerojunk rig and I am thinking of using this kind of arrangement on Little Gypsy Girl (if she does not sell first!)


    Anonymous, thanks for rotating my sketch upright.

    Last modified: 24 May 2018 10:23 | Anonymous member
  • 24 May 2018 03:05
    Reply # 6257596 on 6191276

    I am going to use a detail similar to David's aft-facing tabernacle idea, but here is a photo which might offer an improvement to the sliding sleeve: glass fibre bandage on the mast tube. I did it in preparation for a heel block casting, probably unnecessary but mainly to see what would be the rate of thickness build-up, for future use. But the point here is: it looks as though it would make a nice hard, slippery surface for a round sleeve to slide down over - and with a little sanding it might be also a good way to get just the clearance you want, if perfectly paired tube diameters are not available. Shown here is epoxy and glass cloth wrapped around three times, but there might be better materials for a lubricated aluminium outer tube sliding fit. 

    It was very easy to do. But, I am sure the idea must have been already thought of - and I've never tried it - so...

    Last modified: 24 May 2018 03:34 | Anonymous member
  • 18 May 2018 18:04
    Reply # 6242640 on 6191276
    Mark Thomasson wrote:

    One thing I have no experience of is how easy it is to slide down the sleeve - I take it that it has to have sufficient slack so that it will not bind, yet not too much that there is a wobble.

    This is the thing that I've found difficult with it, when helping Robin, and I can confirm your conjecture, Mark. The outer sleeve and the mast, both being aluminium, are not the best of pairings for sliding, and so there has to be some slack - but not too much. Also, the sleeve is heavy enough that it would be difficult to raise the mast single-handed, keeping the sleeve up above the hinge while pushing the mast up. Maybe the sleeve can be taped in the raised position, otherwise it always seemed to me to be a two person job. Once the sleeve is lowered over the hinge, the upper end has to be taped, so that the parrels don't stick on the step on the way down, so that the reel of duct tape is to hand anyway.

    This hinge + sleeve arrangement is neater than a tabernacle, for sure, but I prefer the tabernacle in the form that I've mentioned, with the pin at the lower end and the opening of the 'U' facing aft, for greater ease of operation. I have it on my 12ft dinghy, I had it on an 18ft dayboat, and I think it scales up to larger boats quite readily, as it was the method used in the Yorkshire and Northumberland Cobles, in sizes up to at least 30ft.

  • 15 May 2018 16:34
    Reply # 6200639 on 6191276
    Deleted user

    Did my upgrade get lost too? Try ...

  • 15 May 2018 11:04
    Reply # 6191731 on 6191276

    Thanks David,

    I knew someone would help out and put it in its correct location!! One day when I am not quite as busy as I am now I will have to try and figure out how to do this sort of thing correctly!!

    Any comments? I have not actually built one but went through the whole design exercise before finally deciding to use a wooden mast and tabernacle on Gypsy Rose.

    Thanks, David.

    PS. I note that the sketch did not get copied over so posted it again

    Last modified: 15 May 2018 11:06 | Anonymous member
  • 15 May 2018 10:45
    Message # 6191276
    David Webb wrote:

    Robert Tay wrote: 

    i am a new member with a junk rigged boat I been struggling with putting a hinge and realise sprit sail is probably best (thames barge style) so I'm on the wrong site I've put an ad up to sell my rig I am currently pedalling inland waterways (pushing lexia with my pedal powered cabin cruiser) I realy wanted junk but the hinge problem seems too big for me I'd pay for off shelf solution but none seems to exist.

    I posted a suggestion that he keep his existing mast and junk sail and modify it with a hinge above deck and a sliding sleeve to provide the stiffness required by the mast. Please see attached sketch for a further explanation of the concept. It is a photo of a hand drawn sketch and is not to scale as I do not know what size mast Robert is dealing with. We are in the process of moving house and I do not have access to more accurate means of drawing. The sleeve should have a 3 to 5mm clearance around the existing mast and should lap the mast each side of the hinge by no less than 10% of the distance from the hinge to the mast top. Preferably 12.5%. The hinge blades should be minimum 12mm for masts up to 150mm diameter. All welds should be full poenetration welds, ground smooth after completion The sleeve section should have a wall thickness of at least as much as the mast section. The sleeve should have a couple of tabs fastened at the bottom which can be used to hoist the sleeve up so that the mast can be hinged down to the deck, if the topping lifts are run through a block at the top of the mast, they can be attached to these tabs, which allows the sail bundle to drop to the deck, as well as not requiring any additional rigging to raise the sleeve up the mast.  A halyard attached to the bow, with a short prop at the hinge, will allow the mast to easily lowered. Temporary side stays or a helper can stabilize the mast laterally.

    I hope that you find this understandable and it is of some help to you Robert.

    All the best, David.

    Copied and pasted over to the Technical Forum.

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