Drift between halyard blocks

  • 23 Jan 2014 22:29
    Reply # 1481794 on 1481236
    Thanks for your replies folks.  I do have a double block at the masthead at this stage but intend to change to two singles as soon as possible.  I was not thinking of the stresses on the mast but more of chafe, as the lead of the parts to the yard is slightly different to the part going down to the deck.  This is most evident when the drift is only 300 - 350mm, but once I have one panel down, and the drift increases to 1.3m, it is hardly noticeable.  Perhaps if I have two single blocks up there the movement in the blocks will absorb some of the twisting force.  The problem only occurs when the yard swings around in sloppy seas and light winds.  The yard swings to windward and then swings back, wrenching the masthead sideways.  The leverage is astonishing and the top of the mast twitches like a rod with a big fish on it!.  If the wind is steady and the sail is full of wind there does not seem to be a problem.
  • 23 Jan 2014 18:20
    Reply # 1481616 on 1481236
    When I had wing sails, the drift was minimal. It didn't seem to matter a jot. 
    If the mast is not secured against rotation, there will be a problem. If the masthead end of the halyard tackle is a double or treble block, there may be a problem ( I use two single blocks).
  • 23 Jan 2014 09:34
    Reply # 1481329 on 1481236
    Anonymous member (Administrator)

    Stavanger, Thursday

     

     

    I agree that the drift of Johanna is too short, but somehow we seem to get away with it. The tackline  is a bungee so the whole sail can lift a bit when the sail swings out. Since the mast is rather overstrong for the 3 ton displacement, I think the yard, rather than the mast, is the weak part. The main tube is only 65 x 3.5mm so the sideways loads are quite high. However, since I reef in mid-F4, it is not a big problem. On both my next boats, Broremann and Frøken Sørensen, I have about 50cm drift, and that looks good.

     

     

    The PJR’s requirement of  a drift of 0.3 yard length would result in a 1.3m taller mast on Johanna than today  -  lots of dead weight. I think 0.3m taller mast would have been fine.

     

    When studying photos of Arion, it seems that the drift is only slightly  on the short side. I suggest you stand at the mast and sight up along it while under sail. If the bend is fairly even, up along it, I would not worry.

     

     

    Arne

    Last modified: 23 Jan 2014 19:40 | Anonymous member (Administrator)
  • 23 Jan 2014 07:42
    Reply # 1481297 on 1481236
    Graham,

    I cant say 100% for sure but your mast is so massively strong for the amount of sail that you carry, it's probably nothing to be too concerned about. By the time it does become an issue (if ever) you'd have put at least one reef in and the issue will have gone away.

    It's not to say that the wringing loads are not high (they are apparently some of the highest in the rig) but I'd say with amply proportioned metal mast such as your own, there is enough reserve to take care of it.

    I think it's more of a concern for wooden mast's but then I've seen a lot of boats with wooden masts that do not have the correct drift (including all of Arne's boats and Peregrine) and I have not heard that they have suffered damage due to wringing loads.

    As to lengthening your mast, I'd try sell it first and then replace the whole thing. If that is not viable, I think I'd try lengthening at the base as it would be possible to massively reinforce the join without needing to be concerned about weight issues.  You'd definitely want to research this topic because I suspect welding would be a no, no unless you can get the mast re-tempered. The strength of aluminum welds is not good being about 80% of that of the base metal.

    One thing you could possibly consider... A redesigned lower aspect sail might give you what you want without having to do anything to the mast.

  • 23 Jan 2014 05:01
    Message # 1481236
    This matter has been discussed elsewhere (by me and others) but I wanted to ask members for specific comments on this topic.  PJR recommends that the top of the mast should be 0.3 of batten length above the sling point on the yard when the sail is fully hoisted.  On Arion, with a batten length of 4.6m, this would be 1.38m.  My clearance is actually about 500mm and the drift between the halyard blocks must be about 300mm.  Boats like Peregrine seem to get away with it and I have sailed Arion very hard, but have become nervous of the wringing action on the masthead when the yard slams about, as it does in certain conditions like light winds and sloppy seas.  My mast is massively strong but I have noticed the masthead whip in these conditions and am now sailing with one panel reefed in all but the smoothest seas.  This is annoying though because Arion is a boat that likes all the sail it can carry.  I have 36sq m for a displacement of 5 tonnes and would like 10% more sail area for light winds. I am thinking that one of these days I might take the mast out and add a metre to the top of it. Of course if I added 10% (an extra panel perhaps) I'd have to go up another 2 metres!   What do others think?
    Last modified: 23 Jan 2014 05:02 | Anonymous member
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