Mast materials and Specifications

  • 19 Mar 2014 20:31
    Reply # 1521082 on 1520471
    Jerry Stebbing wrote:I concentrated instead on contacting UK suppliers who sourced their products from these two manufacturers. Unfortunately none of them replied to my emails with the sole exception of ALC in Port Talbot.

    Jerry, you would possibly have been better off telephoning them. Enquiries for one off orders by email might well go unanswered in a busy office.
  • 19 Mar 2014 20:19
    Reply # 1521071 on 1306051
    Deleted user
    Hi Jerry,

    What is the weight of the mast ?

  • 19 Mar 2014 14:10
    Reply # 1520753 on 1306051
    Fatigue life is determined by the total amount of cycling stresses that the material experiences over its life, relative to its yield strength or ultimate strength. I don't believe that hardness or ductility enter into the matter. In practice, both T5 and T6 have proved completely satisfactory in service, so long as the stress they experience is kept below a certain level. I gave design figures for each that have proved satisfactory.

    In the end, it's performance in service that's the important thing, and my experience with the same section and spec of mast in Tystie leads me to believe that it will be fully satisfactory in your Rustler 31 also.
  • 18 Mar 2014 22:59
    Reply # 1520471 on 1306051
    Many thanks for the responses.

    Brian, I found that buying a single aluminium tapered tube direct from Nedal or Valmont (as mentioned in the links) would be uneconomical due to the enormous delivery costs involved so I concentrated instead on contacting UK suppliers who sourced their products from these two manufacturers. Unfortunately none of them replied to my emails with the sole exception of ALC in Port Talbot. I can't really blame them. Their primary business is bulk orders of lamp posts from local authorities etc and single orders of non-standard products are probably more trouble than they're worth.

    David, I had another look at the PDF drawing of Roger Taylor's lighting column to see if I'd misread the alloy temper, but it definitely says T6.

    I'm no metallurgist but I know that higher tensile steels, although stronger, can be more brittle. Does this apply to aluminium alloys, eg, is the softer T5 less prone to fatigue than the harder T6?


  • 18 Mar 2014 03:09
    Reply # 1519740 on 1519479
    Jerry Stebbing wrote:I'm about to buy an aluminium conical pole from ALC for my Rustler 31's new mast but just wanted to seek advice on a few details before I place a firm order.

    I've basically gone with similar dimensions to Tystie, ie 222mm diameter with 5mm wall thickness. According to the online junk rig calculator this has a breaking strength of 4975 kpm, and my boat (2.743 metres beam, 5250 kg disp) is shown as having a righting moment of 3200 kpm. I think Tystie is quite a bit heavier and with more sail area than my Rustler so I'm hoping I should have a decent safety margin. Any thoughts?

    ALC have sent me an example drawing of a stock 5mm wall thickness lighting pole 9.2 metres overall with 222mm base dia and 90mm top dia. My pole will be 11.7 metres overall. Is 90mm a good choice for the top diameter?

    The drawing of Roger Taylor's lighting column specifies 6005A T6 as the aluminium grade used, but the drawing for the 9.2 metre x 222mm x 90mm x 5mm column shows 6063 T5. I'm not sure yet whether I can specify a particular alloy for my special order pole but which would be the preferred grade if I'm offered the choice?

    Jerry


    Yes, you will be OK with the 222mm dia mast. The calculator in junk FAQ/masts gives a safe stress, not a breaking stress.

    I cut a metre off the top of my pole, to get to a top diameter of 100mm. I think that 90mm is too small for this size of mast ( as you'd also think if you climbed to the top of it).

    Unfortunately, the spin-tapering method cannot be used on the stronger alloys. I'm surprised that Roger's pole specifies T6 temper, as I've never seen anything other than 6063T5 alloy specified for these tapered poles. However, 6063T5 is fine in practice, as you are looking for stiffness as much as strength in a mast, and stiffness is not related to strength, only to modulus of elasticity, which is the same for all aluminium alloys.If you should happen to be given a choice, then 6061T6 and 6005T6 are stronger, and 6063T5 is less strong.
  • 18 Mar 2014 00:08
    Reply # 1519636 on 1519479
    Jerry Stebbing wrote:The drawing of Roger Taylor's lighting column specifies 6005A T6 as the aluminium grade used, but the drawing for the 9.2 metre x 222mm x 90mm x 5mm column shows 6063 T5. I'm not sure yet whether I can specify a particular alloy for my special order pole but which would be the preferred grade if I'm offered the choice?

    Jerry, 6063 T6 would be the preferred grade. 6005A T6 is acceptable. I would not even contemplate a T5 grade aluminum, it is just to soft.
  • 17 Mar 2014 23:29
    Reply # 1519623 on 1519479
    Jerry Stebbing wrote:
    Sourcing a suitable tapered pole for a junk rig mast  in the UK has proven to be more difficult than I envisaged but it looks like ALC could be the answer. I'll let you know how I get on.

    Jerry, did you check out the suppliers mentioned in Junk Info> Useful Links> Sails, Masts and Gear?
  • 17 Mar 2014 20:25
    Reply # 1519479 on 1306051
    I'm about to buy an aluminium conical pole from ALC for my Rustler 31's new mast but just wanted to seek advice on a few details before I place a firm order.

    ALC sent me a technical drawing of the lighting column supplied to Roger Taylor for Mingming 2. It measures 13.7 metres overall but is actually listed as a 12 metre pole, with an additional 1.7 metre section that's normally buried in the ground. The lowest part of the column has large cutouts for cable entry and a service door so Roger had to discard a sizable chunk of his column to end up with a useable mast.

    When I mentioned this to ALC they told me I could have a pole made to order by Nedal with almost any combination of dimensions, and with no fittings or cutouts for hatches etc. The only catch being a wait of up to 3 months for it to be made and delivered.

    I've basically gone with similar dimensions to Tystie, ie 222mm diameter with 5mm wall thickness. According to the online junk rig calculator this has a breaking strength of 4975 kpm, and my boat (2.743 metres beam, 5250 kg disp) is shown as having a righting moment of 3200 kpm. I think Tystie is quite a bit heavier and with more sail area than my Rustler so I'm hoping I should have a decent safety margin. Any thoughts?

    ALC have sent me an example drawing of a stock 5mm wall thickness lighting pole 9.2 metres overall with 222mm base dia and 90mm top dia. My pole will be 11.7 metres overall. Is 90mm a good choice for the top diameter?

    The drawing of Roger Taylor's lighting column specifies 6005A T6 as the aluminium grade used, but the drawing for the 9.2 metre x 222mm x 90mm x 5mm column shows 6063 T5. I'm not sure yet whether I can specify a particular alloy for my special order pole but which would be the preferred grade if I'm offered the choice?

    The price I've been quoted is about £900 + £300 delivery + vat which seems pretty reasonable. I haven't asked yet about anodizing but I imagine it would add considerably to the cost. I'll probably just buy the pole with a raw finish and add my own etch primer and 2 pack gloss.

    In my search for a mast I also considered steel conical poles as an alternative, however the quote I received from Fabrikat in Nottingham for a 3mm wall thickness pole was only slightly lower than ALC's aluminium pole. And Mallatite (Fabrikat's main competitor) were less than helpful with their 'technical expert' telling me it would be almost impossible to calculate the loadings a sail would impose, and hence he couldn't sanction the use of one of his company's columns for use as a yacht mast. I tried reassuring him that Fabrikat poles had been successfully used on yachts (eg Paul Fay) but all to no avail, so I gave up on them.

    Sourcing a suitable tapered pole for a junk rig mast  in the UK has proven to be more difficult than I envisaged but it looks like ALC could be the answer. I'll let you know how I get on.


    Jerry


    Last modified: 17 Mar 2014 20:26 | Anonymous member
  • 09 Mar 2014 22:21
    Reply # 1514001 on 1306051
    Arne,
    I really like the simple mast step along with way the mast is held in place in place on Froken Sorensen. I think it would work well on the Com-pac. The '86 Com-pac doesn't have the hatch but the mast will go about where one would be. Supporting floor structure and a forward bulkhead made the choice for mast placement easy. The location also fit well to allow copying Broreman's sail form with its measurements making it easy to scale up. Thanks for making so much straight forward and thought stimulating information so available



  • 09 Mar 2014 09:57
    Reply # 1513731 on 1306051
    Anonymous member (Administrator)

    Stavanger, Sunday

     

    Hi Phil,

    That Com-pac 16 seems to be a fine little pocket cruiser. I guess you are to put the mast through the fore hatch, or?

    Anyway, you are right about the partners of Frøken Sørensen: I made the mast hole as an almost tight fit and then just secured the mast with two wedges in slots. These are being held in place with a hose clamp below deck. This hose clamp also holds two more strips of wood. They are set up against the deckhead and their purpose is to hold the mast from jumping out of the step. Frøken Sørensen is not meant for OSTAR, so I find this simple method safe enough for my use. It was just a little step up from the way I stepped the second mast for Broremann ( ..see the file “20110630 Getting Broremann....”). In that boat, I made the hole in the deck a bit roomy. Then I just bandaged the mast with webbing, using carpet tape, and topped it with sports tape. That worked as well, with no noise and hardly any movement.

     

    Good luck!

    Arne

     

    PS: On FS, the mast step was made  (intended) to be a tight fit. Still, after I while it started to move a bit here. Tapping in a couple of small, thin wedges sorted it out.

    Last modified: 09 Mar 2014 10:39 | Anonymous member (Administrator)
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