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aluminum tube mast

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  • 04 Oct 2023 22:49
    Quote
    Reply # 13263110 on 13085575
    Anonymous member

    I may have asked the wrong question. While it may be convenient to fit a 5inch tube into a 5inch ID of another tube, there may be some good reasons _not_ to do so.

    • weight high above the WL
    • cost
    • windage
    • creates a stiffer hard point at join
    • upper portion of tube stiffer than lower

    Some of these are tied together, like weight and cost. There are other considerations as well. Assuming a 6inch tube for the lower tube and a 3 inch tube for the top, the fairing might be rather heavy and the spacer to centre the top tube might be over heavy and stiff. So next thing to do is to calculate which of the various tube sizes I can obtain locally (well within and hour or so) will give a strength that makes sense and weight the least without being overly skinny. My first pick, the 5inch tube, is very much too strong/stiff and probably weighs more than it needs to and has more windage to boot.

    Back to my calculator...
  • 03 Oct 2023 15:18
    Quote
    Reply # 13262338 on 13262213
    Anonymous member
    Anonymous wrote:
     (T6 - 6061 6x0.5inch by 20feet is listed as available at my local distributor), 152.4mm X 1.27mm for those who think in those terms. 
    I think you have a decimal point in the wrong place there somewhere, Len. 0.5 inch is 12.7mm, or 0.05 inch is 1.27mm....
    You are right of course or I should change mm to cm. Funny thing is, that while the US is known to use feet and inches all day long, the distributor I found in the US lists all their tube in mm even though some of them are clearly even inches. Here in Canada where everything is supposed to be metric, everything is listed in inches.... go figure.
  • 03 Oct 2023 08:18
    Quote
    Reply # 13262213 on 13261995
    Anonymous member
     (T6 - 6061 6x0.5inch by 20feet is listed as available at my local distributor), 152.4mm X 1.27mm for those who think in those terms. 
    I think you have a decimal point in the wrong place there somewhere, Len. 0.5 inch is 12.7mm, or 0.05 inch is 1.27mm....
  • 02 Oct 2023 20:37
    Quote
    Reply # 13261995 on 13085575
    Anonymous member

    As the thread title matches my current area of interest. I think I can post a query here.

    So far I have determined (using Arne's hybrid mast, I can use a 6inchx0.5inch thick walled tube for the bottom tube of my mast (T6 - 6061 6x0.5inch by 20feet is listed as available at my local distributor), 152.4mm X 12.7mm for those who think in those terms. I can get T6 - 6061 5 x 0.5 to use for an upper portion (also T4 - 6061 5 inch tubing with wall thickness down to .125 and lots in between). T4 seems to be half-ish the strength of T6. In the T6 tubing the next size down from 5 inch is 4 inch which leaves quite a gap while T4 I can get 4.5 in various thicknesses.

    However, if I can use 5 inch, it will just fit. Does anyone have experience with how close extruded tubing might be to it's nominal size? would sanding down the lapped portion be a reasonable option if the fit is too tight? Considering that the material is the same, would there be any problem with heating and cooling expansion/contraction?

    Last modified: 03 Oct 2023 15:19 | Anonymous member
  • 07 Feb 2023 13:22
    Quote
    Reply # 13087890 on 13087479
    Deleted user
    Anonymous wrote:

    Hi Bill,

    my calcs are very rough and could be plus or minus 20% or so depending on what the actual design is. I had to make quite a lot of assumptions and this could make the result quite different to the actual design. The 3/16 may well work for you as it is close to making a 2x safety factor.

    David.

    Thanks Dave I was going off what a bolger micro applecross as to mast position my sail will be different. the yards and battens will be about 11 ft long  the luff 9.5 ft leach appx 15 ft for the luff  these are just close numbers. thanks bill
  • 07 Feb 2023 03:05
    Quote
    Reply # 13087479 on 13085575
    Anonymous member

    Hi Bill,

    my calcs are very rough and could be plus or minus 20% or so depending on what the actual design is. I had to make quite a lot of assumptions and this could make the result quite different to the actual design. The 3/16 may well work for you as it is close to making a 2x safety factor.

    David.
  • 05 Feb 2023 22:36
    Quote
    Reply # 13085916 on 13085879
    Deleted user
    Anonymous wrote:

    Hi Bill,

     a few rough ballpark calcs show that your sail plan will create a bending moment in the mast of around 1500 foot pounds. This is somewhat of a guestimate as I do not know the distance from the center of effort of the sail plan to the deck. The .125" wall pipe has a strength of about 1900 foot pounds and the .1875 of about 2850. This would suggest that the .1875 wall pipe is barely adequate for the task having a safety factor of less than 2.

    David.

    Hi david I was hoping 3/16 inch wall thickness would work. I think steve on cool change a blobster boat is using that are boats are similar thanks have to look into it some more 
  • 05 Feb 2023 22:32
    Quote
    Reply # 13085913 on 13085901
    Deleted user
    Anonymous wrote:

    It might be good for the top or middle part of a mast made from two, or three pieces of tube of different diameters. I made a mast from three pieces, with a fairing at each transition, and it gives a reasonable approximation to a tapered mast. Can you find a short bit of something a bit heavier, to make the base section? It's at the "partners" where the bending forces are greatest, reducing linearly as you go up the mast.



    Hi Graeme thanks for the feed back I al trying to stay with a one piece mast do to it being simple but I like your Ideal 
  • 05 Feb 2023 22:05
    Quote
    Reply # 13085901 on 13085575
    Anonymous member (Administrator)

    It might be good for the top or middle part of a mast made from two, or three pieces of tube of different diameters. I made a mast from three pieces, with a fairing at each transition, and it gives a reasonable approximation to a tapered mast. Can you find a short bit of something a bit heavier, to make the base section? It's at the "partners" where the bending forces are greatest, reducing linearly as you go up the mast.



    Last modified: 05 Feb 2023 22:09 | Anonymous member (Administrator)
  • 05 Feb 2023 21:09
    Quote
    Reply # 13085879 on 13085575
    Anonymous member

    Hi Bill,

     a few rough ballpark calcs show that your sail plan will create a bending moment in the mast of around 1500 foot pounds. This is somewhat of a guestimate as I do not know the distance from the center of effort of the sail plan to the deck. The .125" wall pipe has a strength of about 1900 foot pounds and the .1875 of about 2850. This would suggest that the .1875 wall pipe is barely adequate for the task having a safety factor of less than 2.

    David.
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