Tapered lamp post on ebay

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  • 13 Jan 2022 12:55
    Message # 12259519

    Seen on eBay.

    tapered aluminium lamp post

    ebay item 174517292303 

  • 15 Jan 2022 14:00
    Reply # 12264812 on 12259519

    Good find!

    More info - that's the UK version of Ebay.  The poles concerned are in Lancashire, and are quoted as:

    Length 11m

    Base diameter: 200mm

    Top diameter: 75mm

    Thickness: 6mm

    Inspection cover - 3m up from the base

    Price £295 + VAT

    https://www.ebay.co.uk/itm/174517292303?hash=item28a20a8d0f:g:wBMAAOSw2KVfrt1M


    Thanks for finding that!  I'm tempted, but probably won't bite...

    Last modified: 15 Jan 2022 14:01 | Anonymous member
  • 19 Jan 2022 18:49
    Reply # 12282574 on 12259519

    does anyone know if the part of the mast with the acces panel in it can be used, or would need to be cut of, or could a peice of alu be welded in? thanks

  • 22 Jan 2022 17:29
    Reply # 12300289 on 12259519

    I'm surprised nobody more knowledgable than I has come along...

    I recall this has come up in discussion before.  The hole definitely weakens the mast.  I have seen people suggest welding the door shut; your idea of welding a plate looks better.  I think previously, I've seen a suggestion to not use that portion of the tube, but as it's reported being 3m up an 11m mast, that wouldn't leave so very much!

    I suspect it partly comes down to how good a weld you can achieve, and whether the welding heat would affect the temper of the alloy; I'm afraid I'm no metallurgist, and all my own welding has been to steel, and of "agricultural" quality!

    As my need would be for a longer mast than 11m, if I were to use this, I would be using it as a top on to a probably wood lower section.  I would consider lengthening the wooden plug to extend beyond the opening.  Heavy, yes, but the weight is relatively low.  I won't though.  I'm not 100% convinced about all the details in the listing (eg wall thickness - at top or at the base?).  It's a few hundred miles from me, so a long way to go to inspect it, and a long way to arrange transport for it.

    But it's a good price...


  • 22 Jan 2022 19:08
    Reply # 12300941 on 12259519

    I suggest considering using aircraft structural metal repair techniques, rather than welding. They utilize rivets. if it's good enough for the airline industry it should be good enough for us.

    I once worked for an aluminum boat manufacturer and participated in the building of Canada II, a contender for the America's Cup. I got to see how devilishly hard it is to weld aluminum. Molten aluminum shrinks quite a bit when it cools. I made the parts for a large sheave for the forestay to be located below decks  to receive the forestay. When it was welded, it was so badly distorted it had to be scrapped. They had a local machine shop mill one from heavy plate. 

    I'm not sure I would want to do it myself, using rivets, but would look for someone locally who was qualified. That could prove expensive.  Rather than assume that, however. I'd do more research. Perhaps with the right tools, materials and technique, you can do it yourself.

  • 23 Jan 2022 09:06
    Reply # 12303319 on 12259519

    It's impossible to say what can be done, without a physical inspection. Commonly, tubes like this, with an access hole, have some form of reinforcement such as a sleeve at that point. What can be said for sure is that any form of further work will weaken the tube. Welding certainly will. Rivets certainly will.

    Supposing that the lengths quoted are accurate, this might serve as the foremast for a schooner, or as the mast for a single sail of modest AR when cut down to ~ 8 metres. I remember that the 24ft Mingming II has a mast of this diameter, so maybe it would be suitable for a similar boat meant for rugged cruising. Whether it would be serviceable at a greater length would depend on an inspection.

    As it happens, I am due to be in Preston one morning this week, and it's just possible that I could get to Nook Lane to have a look. If so, I'll report back, as this tube ought to go to a good home on a JR boat of some kind. 

  • 24 Jan 2022 12:58
    Reply # 12308850 on 12259519

    Seem to recall critical loading for a regular mast is the compression induced via the stays. However for unstayed JR mast should be the righting moment with maximum bending stresses near the partners. For argument's sake if you positioned the access hole between the keel and partners then avoids region of highest shear force and bending moment. Having said all that, I'd fair off the hatch and over-wrap with carbon/epoxy prepreg. Shrink tape and a hot air gun. Cheap, quick and reliable solution?


  • 24 Jan 2022 15:17
    Reply # 12309279 on 12259519
    Anonymous member (Administrator)

    How about using a lamppost salvaged from a car accident with the no parking sign still attached - see file from 1964


    1 file
  • 24 Jan 2022 18:39
    Reply # 12309958 on 12309279
    Anonymous wrote:

    How about using a lamppost salvaged from a car accident with the no parking sign still attached - see file from 1964


    That's Ilala. Screengrab from a Pathé newsreel taken at the start.. Not a recommended sail design, but she got across. 
    1 file
  • 24 Jan 2022 21:34
    Reply # 12310662 on 12308850
    Chris wrote:

    Seem to recall critical loading for a regular mast is the compression induced via the stays. However for unstayed JR mast should be the righting moment with maximum bending stresses near the partners. For argument's sake if you positioned the access hole between the keel and partners then avoids region of highest shear force and bending moment. Having said all that, I'd fair off the hatch and over-wrap with carbon/epoxy prepreg. Shrink tape and a hot air gun. Cheap, quick and reliable solution?


    As I've had occasion to say before, aluminium and carbon should never be placed in close proximity in a marine environment - they are at opposite ends of the galvanic table, and the aluminium is quickly eaten away. And materials of differing elasticity should not be asked to carry a load together - the stiffer one carries all the load until it breaks, then the less stiff one carries all the load.

    But still, if the full length of the tube is needed, and if the access hole is well above the partners and has already been sufficiently reinforced with an internal sleeve, and all that is needed is a fairing layer, then glass/epoxy will do well enough.

    Another way to lose the potential weakness of the access hole is to cut the tube at that point and mount the mast in a tabernacle, so that it is ~ 8m LAP, or apparently ~ 9.5m LOA, rather than only ~ 8m LOA. 

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