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  • 30 Oct 2020 01:43
    Reply # 9334776 on 9327660

    Ueli!

    I am in agreement with you. I will be ordering the 8 in pole with 5/32 wall. It will be beautiful


    Karl.

    Nice argument up top there. I got plenty of strognes on the cabin ceiling and will take your advice on a deeper well for the foot. 15 cm sounds good to me! Also, how much do you trust that strap on collar? Think it would keep the mast in the boat on a roll? 


    Do y'all like using shims on the mast partner or spartite? We have some cedar shims at work that I could use... Then again, Spartite has it's advantages. How much do I need to oversize the upper mast partner for ether? 


    I'll soon be asking about rigging and the sorts. I am a rigger on land and am really excited to start in on that aspect of the project. Check out the insulation I am working on now! It has been interesting to rig up the banana shaped pieces and get them to there matting partner at just the right angle. (No lifting points were included) FUN!!!

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  • 29 Oct 2020 09:22
    Reply # 9332860 on 9327660

    Hi Jeffrey,

    I am not at all qualified to give any advise to an ocean sailor, but my opinion to the mast foot is influenced by my small coastal cruisers plan where it says the foot should be 12-15 cm deep ( more than 3 inch collar ) and should be made from a solid wood block or laminated plywood pieces glued together with epoxy. I further glued the foot with wood flour epoxy mix to the bottom of the boat and with the stern side to the A bulkhead. This is altogether yery strong and I would dare to use my boat even on the coast if it were not 450 km away. For the mast partner I had to strengthen  the deck with 3 layers of 12 mm marine plywood to fit the camber of the deck and the diameter of the hole was determined by my carbon mast size of 55 mm OD. A strap on collar is fitted directly under the deck so the mast is held down and can rotate and cannot jump out of its foot which will never happen on the lakes I sail. I hope this helps you a bit what to decide on your mast. The first picture is my mast foot and the second one is of the mast partner from the side with my wooden concoction for raising the mast and dropping it in the hole which is easy with a dressed carbon mast of 6,10 metre length and a total weight of 6,3 kg. Happy building.

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  • 29 Oct 2020 04:36
    Reply # 9332579 on 9327660

    hi jeffrey

    for crossing oceans i might even like to have a bit more than the safety factor of two times the max. righting moment (wich is what your 8"-5/32" mast offers…)

    ueli


  • 28 Oct 2020 21:53
    Reply # 9332013 on 9327660


    Well thanks for all the good advice all. Very much appreciated!

    6061 t6 aluminum is not available in the dimensions needed so I'm stuck with 6063

    So my options available are;

    7 in OD, 0.156" wall - I got 2030 kpm witch is over my safety factor by a bit (1,306 + 50% safety factor= 1959???)

    8 in OD, 0.118" wall - I got 2026 kpm interesting how it went down in strength)

    8 in OD, 0.156" wall-  I got 2662 kpm well over my safety factor and here is the kicker


    The weight difference between the 8in and 7in pole is listed at 13 pounds.(134lbs & 121lbs) So my choice is pretty obvious.

    The scantilines will be something to figure out. I have a very good bit of plywood on the caben roof. (Getting glassed to the "over built" bolk heads) The floor of the boat will be done next. I remember Arnie talking about a method in witch he cold move the foot of the mast around to fit but I am a glutton for pain. Going to try and get the perfect position for the foot and cross my fingers. Y'all think a 3 inch collar is deep enough to hold that foot in place? Any ideas for keeping it down in there? Any cheap products that I can use in place of spartite? Diameter for the upper mast partner hole???


    Told ya I got more questions... 

  • 27 Oct 2020 11:11
    Reply # 9328198 on 9327660
    Anonymous member (Administrator)

    Jeffrey,

    I certainly don’t dare to make very strong rules here. From the early days of western junkrigs there have been two schools of thought:

    Hasler’s and McLeod’s work resulted in very stout wooden masts. Even after I had trimmed their scantlings down a bit, those masts came out very strong (and heavy).

    On the other hand, there were the junkrigs from Sunbird Yachts with masts from Needle Spars. These masts were terribly thin, and could be seen bending and whipping even under moderate loads. The photo below, of a Sunbird 27, was nicked from a brochure dated 1983. Nevertheless, these masts held up, at least for a number of years, when a few of them suddenly came down.

    The lower section of the mast of my IF, Ingeborg is Ø150 x 5mm with a yield strength of about 250MPa. That gives a max bending (yield) moment of about twice the righting moment of Ingeborg. This appears to work fine, without anything near the ‘Needlespar bend’, even when sailing Ingeborg on her ear. However, I only do coastal and inshore sailing. When writing Chapter 6b about the aluminium-wood mast, I therefore suggested one should go up 50% in strength if one plans for offshore cruising. I can only guess on this. However, I also keep the weight of the mast in mind. Ingeborg’s mast only adds 2.5% mass to the boat’s. The last hollow wooden mast I used on my Albin Viggen, Malena added about 5% to her displacement. The extra inertia was noticeable in a headsea, but I would not call it a show-stopper.

    As for deciding the scantlings for taking a full roll-over  -  I have no idea  -  I don't do rollovers...

    Arne


    Last modified: 27 Oct 2020 16:35 | Anonymous member (Administrator)
  • 27 Oct 2020 07:38
    Reply # 9327941 on 9327660

    I think you're right to lean towards the 8 inch, thinner wall tapered tube. Two pieces of empirical evidence:

    Roger Taylor, Mingming II, went for a mast of this size, for the exposed kind of cruising that he does. He feared that it might look over-sized, but once he'd got it stepped and sailing, he thought it looked OK, and as far as I know it performs well.

    I chose a 165mm x 3.2mm / 6.5in x .128in mast for Weaverbird, a smaller boat, but still intended to be capable of taking some rough weather when needs be. This has turned out to be very satisfactory.

    A larger diameter and thinner wall always gives a better strength/weight and stiffness/ weight ratio than a smaller diameter and thicker wall.

  • 27 Oct 2020 07:24
    Reply # 9327907 on 9327660

    Hi Jeffrey,

     according to my rough calculations the 6 inch mast in 6061 T6 aluminium should give a working stress safety factor of about 2.5, which should be OK for most applications. The ultimate stress safety factor is over 3. If using 6063 T6 then the working stress safety factor would only be about 1.5 which would not be adequate.

    All the best with the project, David.

    Last modified: 27 Oct 2020 21:15 | Anonymous member
  • 27 Oct 2020 01:03
    Message # 9327660

    The split junk going by the name "hot dog" is really starting to take shape. The cabin ceiling  is reinforced. The bolk heads and flooring are cut out and just waiting for better weather to glue in.

    It is a contessa 26 with a 305 square foot split junk rig design. This is my first build and I will have many more questions in the very near future. I am going to stick them all into this heading as to better keep track of it all. Know that I spend many days looking through this website and reaching as much as possible before reaching out for help. Thanks in advance for all of the time and effort that everyone puts onto this sight. Thanks a million!


    So... I am trying to get an idea of a proper size mast. I did the math (my little sister might have helped a little). The 6 in OD with 1/4 in wall will not meet my safety factor. So do I look at 8 in. OD with thinner wall or stick with the 6in with heavy wall? I'm leaning towards the 8in option. As I would like to take this boat around the world and back.


    Hear are the status i am working with.(open to interpretation)

    Boat length-25'6"

    Length at water line-20ft

    Beem-7'6"

    Keel-long

    Displacement-5400lbs

    Righting moment-178???

    LR-.533m???

    Max righting moment-1306???


    So what would y'all recommend? 

    PS. I'm working with 6061 tapered aluminum

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