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Birdsmouth mast taper

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  • 23 Nov 2012 00:07
    Quote
    Reply # 1143871 on 975321
    Anonymous member
    The supplier couldn't provide yield strength, but I found some data online for 6061 T6 aluminum 6" tube 1/8 wall diameter:

    Ultimate 
    KSI    		 42
    Ultimate shear strength 
    KSI    		 27
    Yield 
    KSI    		 37

    Unfortunately I couldn't find the same for the 3/16 wall.
  • 01 Nov 2012 21:58
    Quote
    Reply # 1120681 on 975321
    Anonymous member (Administrator)

     

    Karlis

    I bet the supplier can also give you the breaking og yield strength of the tube. I suggest you ask them what that is.

    Arne

     
  • 01 Nov 2012 21:11
    Quote
    Reply # 1120658 on 975321
    Anonymous member
    Just talked to the metal supplier in Nanaimo. They have 6" tubes at 1/8" wall, or a 5.56" OD (5" ID) pipe with a 1/4" wall, at about double the weight of the 6". It's all 6061 alloy T6 temper.  

    The hullform isn't really wineglass, more of a stemware chamberpot. There's a few pictures:

    http://karlis.ca/tmp/IMG_3289.JPG
    http://karlis.ca/tmp/IMG_3291.JPG

    Do you think the 6", 1/8" wall would suffice for coastal cruising? Or should I keep looking?
  • 19 Oct 2012 02:41
    Quote
    Reply # 1107837 on 1107668
    Anonymous member
    Karlis K wrote:Thanks for a great resource. I'm a little envious that the 22' hurley gets a recommendation like 5" dia with 3/16" wall while I'm looking for a heavy spring scale a winch and a calculator. Any suggestions for a  24', 4000 lbs./ 1814 kgs tubby vessel with a 30sqft cambered johanna-style?  Fantail, which compares in sail area and displacement, uses a 152mm/6" tube (JRA issue #58), and I'd be OK try that size, but what wall thickness and aluminum grade?
    Fantail is actually 2500 kg displacement, but of a "wineglass" kind of hull form, that doesn't have as much form stability as a chine hull, for example.  6" x 3/16" tube should have a generous margin of safety, when used with the same size sail as Fantail. 5" x 3/16" is rather small, and I doubt whether 5 1/2" x 3/16" is readily available. You're looking for 6000 series aluminium (6061 if available), with a temper of T6. 

    Could you fill in some details of your boat in your profile, please, Karlis? That helps folks to be more specific when you're requesting advice.
  • 19 Oct 2012 01:12
    Quote
    Reply # 1107668 on 975321
    Anonymous member
    Thanks for a great resource. I'm a little envious that the 22' hurley gets a recommendation like 5" dia with 3/16" wall while I'm looking for a heavy spring scale a winch and a calculator. Any suggestions for a  24', 4000 lbs./ 1814 kgs tubby vessel with a 30sqft cambered johanna-style?  Fantail, which compares in sail area and displacement, uses a 152mm/6" tube (JRA issue #58), and I'd be OK try that size, but what wall thickness and aluminum grade?
  • 18 Oct 2012 19:19
    Quote
    Reply # 1107425 on 1106938
    Anonymous member
    Karlis K wrote:Are you using a formula or rule of thumb for aluminum mast sizes, either from scratch or for converting from PJR wooden mast calculations? 

    For example, I have a 9m (head to step) birdsmouth mast with a 20cm diameter at the partners and approx 38mm wall. How would I calculate the aluminum base replacement for a hybrid mast? 
    I put some notes on calculating the tube size in "Ask the Junkmaster/Masts"
  • 18 Oct 2012 06:11
    Quote
    Reply # 1106938 on 975321
    Anonymous member
    Are you using a formula or rule of thumb for aluminum mast sizes, either from scratch or for converting from PJR wooden mast calculations? 

    For example, I have a 9m (head to step) birdsmouth mast with a 20cm diameter at the partners and approx 38mm wall. How would I calculate the aluminum base replacement for a hybrid mast? 
  • 23 Jul 2012 07:01
    Quote
    Reply # 1017076 on 975321
    Deleted user

    Mark,
    Vanharouvas mast is made of a aluminium tube 150x5 mm, 4,9m long and the top is made of a glassfibre flagpole 140 mm bottom end. I reinforced 2,5 m from bottom with directional fibres and epoxy. The hole length is 9,5 m. The top diam is ab 95 mm.
    The tube seems a little overkill but 150x3 mm was  the alternative and it seemed too thin.
    Robin F
  • 11 Jul 2012 22:42
    Quote
    Reply # 1006056 on 1005680
    Anonymous member
    Mark Thomasson wrote:

    Have a look at Oryx's mast, photo in my profile - albums.  Pete built a square box with triangular fillets inside, then ronded the square & covered in glass/epoxy.  Sounds about as easy as you can get.  Also tabernacle mounted.

    A general question for all - For a boat this size, would an aluminium mast be easier to make?  or aluminium / timber, as Annie's?

    Mark,
    an all alloy mast depends on being able to get a long enough tube, either tapered or un-tapered. That makes it difficult and/or expensive. I still favour the hybrid mast - alloy tube/wooden topmast - as being the way to get a mast with the least investment of skill, work, money and time. 
    Paul,
    For a Hurley 22, I would be thinking of an alloy tube 5" diameter, 3/16" wall, 5 or 6 metres long, with a wooden topmast made by any of the staved methods. Being only 3 or 4 metres long, with no curves in the staves, the build is very straightforward.
    Last modified: 11 Jul 2012 22:50 | Anonymous member
  • 11 Jul 2012 14:08
    Quote
    Reply # 1005680 on 975321
    Anonymous member

    Have a look at Oryx's mast, photo in my profile - albums.  Pete built a square box with triangular fillets inside, then ronded the square & covered in glass/epoxy.  Sounds about as easy as you can get.  Also tabernacle mounted.

    A general question for all - For a boat this size, would an aluminium mast be easier to make?  or aluminium / timber, as Annie's?
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