Mast materials and Specifications

  • 08 Mar 2014 22:43
    Reply # 1513562 on 1306051

    I 'm seeking advice about mast wedges and partner clearance and want to share a little progress and an experience with sleeving a mast. A photo in Arne's Froken Sorenson part I appears to show notches cut for several wedges with a small clearance between mast and partners. I'm wondering if I'm seeing that correctly. On the Com-pac 16 I'm going for a keel stepped mast rather than my original tabernacle plan and don't know much about clearance and wedging. I went with a partially sleeved 3 ½ inch aluminum mast rather than 4 inch which was the obvious choice for strength and weight. The planned tabernacle would have had the mast held in 2 laminated wood blocks, at the pivot and base with the top one hinged with a hefty long bolt. The bolt would have been aft of the mast and through the tabernacle sides and laminated top block. The whole thing with a 4'' aluminum tube was getting pretty wide side to side and fore and aft in proportion to a 16 ft boat. I decided to go with an internally sleeved 3 ½ inch mast then later to drop the tabernacle plan. The 3 ½ inch tube without a sleeve has 27% less bending strength than the 4 inch but still has a safety factor of 1.47 with 400 lbs added to the boats empty displacement of 1100. Adding the six foot snug fitting internal sleeve, four feet of it above the partners, should give me more where I expect most of the stress to be.

    The 14ft. aluminum 6061 t6 3 1/2''x .125 inch tube is sleeved for that first 6ft with a 3 ¼ x .125 in snug fitting tube. The upper 5 1/2 ft. will be wood. Sliding in the first inches as a test showed it to be a tight but potentially doable fit. Tube specs cite very slight allowable differences in diameters and wall thickness and a minor variation or gouging could make it go extra dry. I was preparing for a battle with no turning back but a suggestion by a local machine shop teacher and the cold weather here made all the difference. After going over the inner tube with an emery cloth strip, I set it outside for the night with the temperature at 0 F. The outer tube came in the house at 70 F degrees. In the morning to my suprise and delight I was able to push the tube in by hand and only used the heavy hammer and a wood block lightly to bring it up flush. I'm told that dry ice is sometimes used to contract metal for a fit. I had thought to reduce the hard spot at the upper end of the sleeve by cutting six 10 or 12 inch long very narrow V slots but didn't want complications inserting the tube. Instead I just put a small bevel in the top. With the longer mast planned I added panel 7 back in at the foot so I will have a slightly shortened batten six and a boom shortened by a foot. I guess that should work OK. Doesn't look bad on paper, even closer to that ear listening for the wind.

  • 16 Feb 2014 20:11
    Reply # 1499229 on 1306051
    [Webteam edit: I've moved the following from the forum about Roger Taylor's recent talk, as it will be more useful here in the future. Brian]

    From Jonathan 14.2.2014

    I may be about to replace the mainmast on Lexia (before it fails !?)

    I would therefore also be interested as a matter of some urgency to know what was the source of Roger's lighting pole from which he made his mast.  Also then any comments about the company and his dealings with them and about the suitablility of such a pole and the practicalities of such a conversion.

    It may well be that this information is already published by Roger somewhere.   If so then a link or reference posted here by Roger or A N Other would be much appreciated.

    From Ash Woods 14.2.2014

    Hi Jonathan,

    I have the details as given by Roger in his talk:

    The Aluminium Lighting Company Ltd
    Croeserw Industrial Estate
    Eastern Avenue
    Cymmer
    PORT TALBOT
    SA13 3PB

    Telephone: 01639 852502
    Fax: 01639 852263
    E: sales@alulight.co.uk

    www.aluminium-lighting.com

    I will email you with a spec sheet i downloaded.

    From David Tyler 14 Feb 2014

    Ah, I'd forgotten about this source. The tubes come from Nedal, which is where mine originated, so I'm sure they're fit for the task.

    http://www.aluminium-lighting.com/downloads/columns.pdf

    - the 145mm diameter size might just be what Lexia is looking for.
  • 14 Feb 2014 20:14
    Reply # 1498274 on 1497441
    Jonathan Snodgrass wrote:

    And yes I will ask Roger Taylor for his source of lighting pole, unless any eagle eyed member who knows the answer from his published articles tells me first. 

    Roger provided the details in another fora. They are now in Junk Info > Useful Links > Sails, Masts and Gear.
  • 13 Feb 2014 21:29
    Reply # 1497544 on 1306051
    Personally, I have strong objections to the ingress of water from any source and would find a leaking mast intolerable.  I used large quantities of Simpsons Marine Glue to secure and to seal my topmast.  I made a fillet at the joint and the ropes slide up and down over it with never a problem.  So far.

    If the mast doesn't leak, you don't need to rivet in a conduit but can wrap it in something like closed-cell foam that will tap gently rather than rattle.
    Last modified: 13 Feb 2014 21:29 | Anonymous member
  • 13 Feb 2014 18:50
    Reply # 1497441 on 1306051

    David

    Indeed.  Thank you very much for all that. 

    As regards the taper for the step, I think that Charlie would turn one piece to form the plug (to fit into the top of the bottom section with a hole with a clearance fit for the top section to secure and centry it) and the tapered section. 

    Your comment about water ingress through the top of the taper rings true.  I think that water is getting to Lexia's foremast step and it could well be getting in through the top of the taper.  Charlie Hutton did have some very sticky very strong tape from the Formula One world, and one run of that round the top and bottom of the tape might reduce any water ingress. 

    As regards RI, NY.  No comment.

    And yes I will ask Roger Taylor for his source of lighting pole, unless any eagle eyed member who knows the answer from his published articles tells me first. 

    Jonathan

  • 13 Feb 2014 18:48
    Reply # 1497439 on 1306051
    We do have some links for tapered alloy poles in Junk FAQs:


    and in Junk information/Useful links:

  • 13 Feb 2014 16:16
    Reply # 1497321 on 1306051
    JDS,
    Weight is not an issue. The heavier tube is low down, and above that, you can reduce the diameter substantially if you want to, but take into account that a mast that whips like a fishing rod at the top shakes the wind out of the sails and increases wear and tear. Weight aloft does indeed increase the rotary moment of inertia, but the effect of this is to slow down the roll, not to decrease its amplitude. For example, Badger has a 6 second roll with her two solid wood masts, Tystie has a 3 1/2 second roll with her tapered alloy mast.

    Two more examples: Mingming II has an 8 inch mast on a 24 ft boat, to be proof against all eventualities, and she seems to be carrying it well enough. Fantail has a 6 inch x 3/16 mast on a 26 ft boat, and a sail of the same area as your main, and I saw when I sailed her that it was of the correct stiffness and didn't overburden the boat.
    If you go for "third time lucky", I for one would like to be sure that you have a mast that will get you as far as Newport RI.

    For the step in a two piece mast, I would cut a 6 inch length of 5.562 x 5 inch tube, mount it in a lathe, and turn a taper of 2 degrees. This will leave a tiny step at the top, as I wouldn't want to bring it to a feather edge. I would bond this over the top of the lower tube, and bond the upper tube into the lower, with polyurethane sealant (with a few backup rivets). I've recently had a close look at a pair of mechanically assembled two piece masts, and my hunch was that water was getting into the boat by trickling down the outside of the upper tube, through the join, and down the inside of the lower tube. On Fantail, there is only this bonded joint, no rivets. The contact area is so huge, with a 10% bury, that there's no likelihood of a failure.

    My mast is a one piece tapered tube, like Roger's. Atlantic Spars bought the remaining stock from Proctor Masts, but it's long gone, now. I think Malliemac got the last mast made from this stock.

    I think you'll have to ask Roger directly where he bought his tapered light pole.
  • 13 Feb 2014 12:38
    Reply # 1497194 on 1306051

    MAINMAST FOR LEXIA

    David

    A couple of thoughts. 

    Firstly.  Is weight likely to be an issue? 

    Presumably all weight is to the detriment of performance, except perhaps for the somewhat esoteric notion that weight aloft increases the moment of  ineritia and hence apparently decreases rolling.  Or is that another myth? 

    Presumably increased weight aloft is to the detriment of stability.  Should one be consulting the boat's designer, Alan Boswell, about any increase in the weight of the mast(s).   I strongly suspect that is it not a significant matter, unless one goes for wood or steel, which are not under consideration here. 

    Secondly.  Stepped construction. 

    In order to allow the sail to fall easily under its own weight, a major advantage of the junk rig, I think that we would all like to have tapered or straight masts.  Constucting the mast from a wider bottom mast and a narrower top mast inevitably means having a step.

    On the foremast which was made for Lexia by Atlantic Spars, this step has a tapered cone to minimise the snagging of the batten parrels as the sail falls.  This cone was made of 'plastic' (nylon?) and is relatively short.  It does reduce the snagging of the batten parrels.  In retrospect I would have liked it to be a longer cone with a shallower angle  Charlie Hutton has said that this could be done by making the plug and cone from aluminium alloy. 

    I wondered if you had any similar experience with your similarly constructed Atlantic Spars mast. 

    Finally. 

    I would certainly like to pursue your suggestion of a tapered lighting pole as used by Roger Taylor.  As so often, I recall mention of that somewhere in our proceedings.  I will now try to find the mention and the detail of the company.  However, not being very good at these things, could I ask if you could provide a link?  I suspect that you will beat me to finding it!

    Thanks.

    Jonathan

     

  • 13 Feb 2014 11:33
    Reply # 1497181 on 1306051

    David

    Thank you for your comments.  Helpful and food for thought as always.

    Jonathan

  • 12 Feb 2014 19:42
    Reply # 1496758 on 1496683
    Jonathan Snodgrass wrote:

    The three designs are in increasing strength ( / stiffness ? ) but in increasing weight and cost.

    The first design is the same OD bottom to top, which is more attractive than having a step, albeit a step with a tapered cone. 

    Tube 5" x 3 mm.  10.00 m above deck.  2.14 bury.

    Internal doubler 3 mm to 3.66 m above deck.

    The second design is for a stepped mast with a bottom section of 5" x 6mm wall to 3.8 m above deck and a top section of 42 x 3 mm wall. 

    The third design uses 5.5 " x 6 mm bottom tube and 4.5 " x 3 mm top tube. 

    My current inclination is to go with the first ie the cheapest and lightest design.  

    My first choice would be 6 inch x 3/16 wall tube, but if that is not available, or will not fit, my inclination would be to go with the third design. At least, to go with the bottom tube, which I think may actually be "5 inch nominal diameter schedule 40 pipe" - the actual dimensions being a nominal 5 inch inside diameter, with a wall thickness of 0.258", giving an outside diameter of 5.562". This I would consider to be stiff enough (stiffness is important) and strong enough, and need not have a doubler inserted (my mast was made by Atlantic spars, and has a doubler made in the way that you describe, but I'm not entirely certain that a split tube performs as well as an unsplit tube of the same diameter, and so in my calculations for Tystie, I only took into account half the wall thickness.) This pipe should accept 5 inch tube as the next stage up. From memory, the bigger Needlespar masts were made this way.

    My conduit is riveted in. Over the years, some of those rivets have broken, as even with the considerable stiffness of my mast, there is still some flex, and so some relative movement between the mast wall and the conduit. If I made a new mast now, I would undoubtedly look for a more flexible way of adding the conduit.

    A further thought: Remember how Roger Taylor fared, when looking for a mast for MingmingII? How about asking Charlie to look at buying a tapered alloy lighting pole from the same source, as his starting point? No joins to be made. There are enough junks sailing around successfully now, with masts made from these poles, to have confidence in them.
    Last modified: 12 Feb 2014 20:44 | Anonymous member
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