Use of spreaders

Discussion in 'Sailboats' started by BertKu, Dec 25, 2016.

  1. BertKu
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    BertKu Senior Member

    Hi there is there an advantage of having the spreaders swivel or must they be fixed on a aluminium mast. Bert
     
  2. gggGuest
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    gggGuest ...

    It all depends what you want them to do.

    Pivoting spreaders tend to restrain a mast sideways with very little limitation on fore and aft bend, fixed spreaders manage fore and aft bend in the mid mast as well. A lot depends on what other standing rigging is doing.

    In dinghies swinging spreaders went out of fashion at the same time as heavy long section pear shaped masts which had more fore aft stiffness than modern sections tend to.
     
  3. BertKu
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    BertKu Senior Member

    First at all, Merry Christmas. Thank you for your reply. The best is that I put a photo on the thread. The roll up system I made for the boat has a anodised 2.7 mm thick (+/- 01 Inch} wall pipe of 1 Inch diameter. That is reasonable stiff. The boat will not have a main sail. The large roll up jib is intended only as a rescue system, should my electrics fail, battery, motor, solar system, to bring me to base.

    Therefore the 2 stainless steel wires from the top of the mast are mounted to the back of the mast (as per drawing) I cannot have a wire (rigging} to the back (transom) as my folding up solar panels are in the way. Also my folding down mast needs a travelling rest.

    Thank you for your help. I will make it permanent mounted. Bert
     

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    Last edited: Dec 25, 2016
  4. gggGuest
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    gggGuest ...

    You're a fair bit outside my experience zone, but 1 inch tube for the mast doesn't sound very big. Keep a very good watch on it in early testing to see if the mast is tending to bend under compression loads. If it does then a bit more wire mongery might be enough to stabilise it, or if needed maybe a secondhand alloy spar of greater thickness. I tend to think with shrouds well aft like yours you should have no need for a backstay to do that job.
     
  5. BertKu
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    BertKu Senior Member

    Thanks for your concern. Well, you may be right, but indeed time will learn whether the aluminium pipe will bend too much. Should that be the case, I have space for the stainless steel wire to be mounted in the pipe and get tensed. However the pipe itself will be tensed by the 2 downward wires to a maximum of 200 kg set by me. ( limit 380 kg) , but I calculated that 100 -150 kg is probably enough . However the forces from the wind can be reduced by rolling the sail in. Bert
     
  6. gggGuest
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    gggGuest ...

    If it bends under compression a wire down the pipe will make it worse rather than better.

    What might help would be longish spreaders half way up pushing the mast in and forwards, coupled with extra shrouds to the root of those spreaders which would be pulling it aft and back. That would tend to lock the mid mast in position and help control compression bending. But realistically all you can do is try it out.

    I must say IIWY I'd be inclined to keep my eyes open for an old alloy spar I could relieve the current owner of the trouble of disposing of. Because you aren't doing anything complicated with it an otherwise scrap spar with a long enough good bit in the middle should do you nicely. Murphy's law suggests you'll only be able to get a suitable lump cheaply if you don't need it in a hurry!
     
  7. BertKu
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    BertKu Senior Member

    Thanks.

    I doubt it, that in the conditions i will sail, that there is any massive form of compression bending. Is there any chance you put your suggestion on a sketch or drawing in a thread. I will certainly consider then your proposal.

    In this part of the world, there are not too many used old alloy spars for sale. In the UK, yes. Actually none at present here in the area, which will fit and has the right size. But, yes I will keep an eye open. Bert
     
  8. gggGuest
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    gggGuest ...

    The load from the sail will tend to end up as compression, because your nicely triangulated and well placed shrouds will stop it going anywhere else.

    So something like this. Angles greatly exaggerated for clarity. The red shroud acting on the spreader pushes in and forward, the blue check stay counteracts. Make sure you reinforce the spar at the spreader to cope with the crushing force from the spreader - commercial spreader mounting brackets tend to include this.

    But don't bother unless you see signs of the spar bending under load and needing the support. It might well be good enough, I have absolutely no idea, and refuse to make predictions.
     

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  9. BertKu
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    BertKu Senior Member

    Thank you. That is an interesting concept. I personally don't think I will have a problem. The total height of the mast is 4.6 meter above the cabin and 4.2 meters above the mast holding bracket. The holding bracket is not only lightly supported on the cabin roof, but mainly on the two edges of the boat, where the hull and deck is mounted together. The mast is extra supported at the lower end. But yes, should I have a problem I certainly will try to implement your solution. Thanks for your input.
    Bert
     
  10. BertKu
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    BertKu Senior Member

    Hi, if you were in my shoes, where would you place the 1st spreader on this 4.2 mtr mast and 4.6 meter above the cabin. Also what should be the length of each spreader. The cabin is 1.44 mtr wide and the boat is 1.65 mtr wide. I thought to place the 1st spreader at 2.80 mtr (i.e. at 3.20 mtr above the cabin) and I thought 40 cm in length each spreader. What would be your suggestion?

    You see, I always sailed on wooden boats with wooden mast. I have never seen wooden masts with spreaders.
    Bert
     

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    Last edited: Dec 28, 2016
  11. gggGuest
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    gggGuest ...

    For your purposes its not very critical, about half way up the spar would be good, because you're just aiming to support the middle.

    Spreader length, again its not very critical, at a guess if you set it up so the shroud is deflected about 150mm aft and 150mm sideways that's probably going to be OK. That's possibly on the long side, but better to err that way I think as you won't be using loads of rig tension like a racing boat would.

    The nice thing about this setup with check stays is that none of it is very critical on a small simple boat like this. Rigging it you just set up the 4 shrouds so its pretty much straight with the rigging slack, and then adjust it with the sail up and loaded so the mast is straight in action.

    Spreaders on wooden bermudan masts were common enough back in the day. But all we are doing is seeking to lock the middle of the spar. You could get exactly the same effect with no spreaders, just lower shrouds and an inner forestay to halfway up the spar, but of course an inner forestay would be a considerable nuisance for tacking and gybing - you'd probably end up having to furl the sail for every manouver - so reckon its worth the trouble of setting up the spreaders if the spar turns out to be a bit too bendy.
     
  12. BertKu
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    BertKu Senior Member

    Thank you. It gives me a good idea what to do. I may have to be careful where to place the spreaders as I would not like to have interference from the spreaders when the mast is folded down. There will be times that I will motor with the mast folded up. Thank you so much for the information.
    bert
     
  13. gggGuest
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    gggGuest ...

    If you got lucky you might be able to arrange for the spreaders to act as supports for the folded mast...
     
  14. BertKu
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    BertKu Senior Member

    No I am not so lucky. Although the idea is a good one. I must be able to sail with the solar panels folded up and swivel 80 cm inwards. If the mast is then down, it conflict. Bert
     

  15. BertKu
    Joined: May 2009
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    BertKu Senior Member

    Hi gggGuest, You are right, I have been able to utilize the spreaders as a rest point for the mast. Although I still have to make a bracket to lift the spreader legs from the back of the solar panels. I am concerned that one day, the mast may come too fast down, when the mast gets folded away, that it will damage the solar panels. Attached 2 photo's on the progress of the building. Unfortunately I have to try to resolve a few small problems and love to know from forum members whether the roll on roll off system has 2 ropes, one for pulling the sail in and the other rope to release the sail. Due to the size of the pipe (25 mm) whereon the sail is wound, the pulling force is quite severe and I am worried that on long term the sail will be damaged. This is I think the case if I have only one rope of pulling the sail in and by pulling the sail out with the rope attached to the sail. How are your systems working? Bert

    I have an old sail (3,4 m2) on which I will do all kind of tests before I am ordering a large new 7 - 8 m2 sail.
     

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    Last edited: Jan 14, 2017
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