Galion 22 conversion

  • 24 Nov 2017 13:43
    Reply # 5600031 on 5070195
    Is it possible to use a lighting pole that is not tapered, but "stepped" (I have no idea of the right term in englis) like this?

    They seem to be available in 4 and 5 mm wall thicknesses in various lengths, although sold only in 6060.

  • 24 Nov 2017 12:25
    Reply # 5600007 on 5070195
    Aargh - the seller of the al-flagpole has no certainty of the alloy type, and for some reason he will not specify the manufacturer (which according to him is dutch, but is it a Nedal pole - he will not answer this) for me to find out myself.

    The seller advices me to assume that the flagpole is 6060 alloy, because it is not certain if it is 6062 or not. Blah.

  • 23 Nov 2017 10:09
    Reply # 5599331 on 5598833
    Anonymous member (Administrator)
    Jami Jokinen wrote:Points taken, thanks. 

    I'll wait for the info about the alloy type of the flagpole and go on from there.

    If the tube is 145mm and I will add 6-10mm of glass, how big should I make the hole at the partners (of mast collar, should I have one welded) - to leave suitable amount of space for the wedges?


    Jami,

    That depends on how accurate you are when lining up the mast step and partners. On earlier boats (Malena, Johanna) I made room for quite wide (3cm?) wedges to make sure I could adjust the mast rake to set right, even with a little error in the mast step.

    On Ingeborg I made a (temporarily) movable mast step, then test-stepped the mast and moved the step about 1-2 cm forward to get the mast right. Then the step was screwed and epoxied permanently in place before re-stepping the mast This method lets me have neater partners with only 20mm wedges. I take care to make the wedges with fine angles and with a lip on top to keep them from ever dropping through.

    Arne

    Last modified: 23 Nov 2017 10:11 | Anonymous member (Administrator)
  • 22 Nov 2017 20:47
    Reply # 5598833 on 5070195
    Points taken, thanks. 

    I'll wait for the info about the alloy type of the flagpole and go on from there.

    If the tube is 145mm and I will add 6-10mm of glass, how big should I make the hole at the partners (of mast collar, should I have one welded) - to leave suitable amount of space for the wedges?

    Last modified: 22 Nov 2017 21:11 | Anonymous member
  • 22 Nov 2017 20:17
    Reply # 5598797 on 5070195
    Anonymous member (Administrator)

    Jami,


    What causes stress in an un-stayed mast.

    The two biggest factors, which stress a mast, are sail pressure and the pitching of the boat.

    To minimise the last factor, I have made a habit of making moderately short masts, and then pile on some sail on it.  The original reason for this was that the quite stout and heavy spruce masts I used, would otherwise add too much to the hobby-horsing of the boat (increase ‘pitch radius’). With aluminium, I am more concerned about the whipping of the mast and eventual fatigue, as David mentions, so I still keep the masts as low as I can. I am less afraid of sail area, as the stability of the boat will put limits on how much sail one can carry in a rising wind. The HM-style sailplan lets one set the biggest and tallest sail on a given mast length.

    The rigs I have drawn for your Gallion 22, at least the smallest rig, must be said to have a moderately short mast, which will not add nearly as much stress on itself in a seaway, compared to some tall JR masts I have seen.

    I am not sure if the lower section of your mast will see most stress and need an inner section added. Remember, the pole is tapered. I suggest you try it as it is (with the added GRP around the partners) in moderate and rising winds and then observe it (go to the mast and sight up along it). It may well be that you will spot a nice and even  -  and hopefully moderate  -  bend up along the pole. This is a fine thing with free-standing masts: It gives a quite accurate feedback about how much and where it is stressed. It will scare you long before it breaks.

    Arne


  • 22 Nov 2017 17:35
    Reply # 5598640 on 5070195
    A thought about reinforcing the al-flagpole from inside:

    How much smaller diameter can the inserted al-tube have than the inner diameter of the flagpole? Can it be significally smaller than 140mm (the inside dia) if one would add several glass/epoxy bands to this - in a similar way that Arne suggested with his tube-style alternative to tabernacle? Would this be better or worse than adding glass to the outer side of the flagpole?

    Last modified: 22 Nov 2017 18:05 | Anonymous member
  • 22 Nov 2017 13:56
    Reply # 5597594 on 5070195
    Basically you got it right, David - I see regularly quite strong winds at Bothnian Bay, and I don't see sailing to the North Sea impossible in the coming years. The thought of losing a mast at sea is frightening.

    However, I also have to balance between this and the availability/cost of the materials - as is the situation to everyone else, I suppose.

    Regarding the lifespan of the mast, five years seems too short, ten years would be a lot nicer.

    EDIT: The wall thickness of the flagpole is 2,5mm and not 2,8 as I thought. I don't know how much difference this makes. I have contacted the seller and demanded exact info about the alloy type. 

    Last modified: 22 Nov 2017 15:58 | Anonymous member
  • 22 Nov 2017 13:37
    Reply # 5597587 on 5070195

    I thought that the tapered aluminium tube was a bit marginal. Maybe it's OK, maybe it isn't, but in view of your comment, Jami, that you expected to sail in strong conditions, I came down against it. It won't be a case of short term catastrophe, with failure in the first big blow, but more a case of "what is the service life going to be?", remembering that aluminium alloy does not have a fatigue limit, a fixed level of stress below which fatigue failure does not occur (unlike steel, for example). The higher the stresses, the shorter the lifespan, and the lower the stresses the longer the lifespan, but every aluminium mast is going to fail, eventually. This isn't really a problem, we have to remember that every aircraft flies on the basis that its components have a safe lifespan, after which they need to be replaced. We just have to ensure that the service life is as long as we need it to be.

    But notwithstanding the above, in view of your difficulty in finding anything else, it's looking like it has to be the tapered aluminium tube. So how to reinforce that vital area just above and below the deck? We've eliminated a matching sleeve of aluminium tube as being unavailable. I think I'd put on unidirectional glass/epoxy, with the fibres vertical. A cloth 1 metre wide will go around twice. I'd put on one piece 1 metre long, so 500mm above and below deck, followed by two more pieces, increasing in length, a 2 metre piece and then a 2.5 or 3 metre piece, so that it extends to the heel and then to the same distance above deck.

    Last modified: 22 Nov 2017 13:38 | Anonymous member
  • 22 Nov 2017 13:10
    Reply # 5597564 on 5070195
    Thanks (again), Arne.

    The diameter of the flagpole is 60mm at the top, and since the height is 12m, I could cut about 2 meters. This should increase diameter by 10-20mm (a pure guess). 

    The seller doesn't seem to know (or is too lazy to find out) the excact alloy type. I'll try to press harder.

    Last modified: 22 Nov 2017 13:23 | Anonymous member
  • 22 Nov 2017 08:58
    Reply # 5597471 on 5070195
    Anonymous member (Administrator)

    I can see your point, Jami.

    I am in a similar situation, but for the all-wooden masts I paid a boatbuilder to do the difficult bits, and only did the glassing and painting myself.

    Now I looked up that aluminium flagpole at 145 x 2.8mm.

    Its strength (max bending moment) depends on the kind of alloy used as well.

    If it is 6060-T6 at 150MPa, its yield strength should be 667kpm.
    If it is 6082-T6 at 250MPa, it yield strength should be 1112kpm.

    Yesterday I guessed the righting moment of the Gallion 22 to be around 681kpm
    (M
    r=Disp. x Beam x 0.20). This is the ultimate knock-down righting moment.

    If the flagpole is made of an alloy which brings its yield strength up over 800-900kpm, I would be inclined to try it (if it isn’t too expensive). The British junkies have sailed around for decades with very slim mast profiles and (mostly) got away with it. I think it is better to use a bigger section with thinner walls. These are stiffer, and quite light. I might give the mast a 0.3m tall grp bandage (10mm thick?) at the partners (And mast step?) to reduce the risk of buckling the rather thin-walled section. Can’t hurt.

    What is the diameter of that pole at mast top level?

    Arne

    PS: Again, I haven’t double-checked my calculations, so better look over them.


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