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HFJY34

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  • 09 Feb 2019 16:13
    Quote
    Reply # 7155251 on 7155071
    Anonymous member (Administrator)

    Hi Frederik

    When using the formulas in Chapter 6 of TCPJR, I too came up with a mast diameter of 31cm (hollow spruce). That should give a bending strength of at least 11600kpm

    The other method is to look for an aluminium mast, starting with finding the ultimate righting moment of the vessel: As shown in chapter 6b  -  and guessing the max righting arm to be 0.18 times the beam that, I find that:

    0.18 x Beam x Displacement = 0.18 x 3.05m x 8000kg = 4392kpm

    Depending on sailing ambitions, the yield (bending) strength of the aluminium mast should then be between 8700 and 13000kpm, that is 2-3 times the vessel’s righting moment. I would guess that 10000kpm should do well. The challenge is to find a suitable tube dimension with the strongest temper ( 6082-T6 alloy, at 250(N/sqmm)).

    It appears that a 220 x 5mm tube will only take 4524kpm bending. I guess a 220 tube with 10mm wall (8447kpm) would be better.

    Whatever material you make the mast of, it is a good idea to check its weight against the displacement of the boat. If it weighs 3% or less of the boat, you should be fine.

    Arne


    Last modified: 09 Feb 2019 16:15 | Anonymous member (Administrator)
  • 09 Feb 2019 12:22
    Quote
    Message # 7155071
    Anonymous member

    If I am going to build a boat, it will be this one.

     I asked Chris Morejohn to design this boat for me and with the help of Arne we got the rig looking good.  imo...

    some numbers  

    LOA 34 ft

    Beam 10 ft

    Lwl ca 34 ft

    Draft 20 “ board up  6 ft  board down  

    Displ 6-8 tons

    Main 56 kvm  

    Mizzen 9 kvm

    CE calculated without mizzen

    CLR with rudder and  daggerboard down (small daggerboards aft not included)

    lead ca  15 %

    chord/wl ca  55%

    mast height ca  13 m, ca  11,5 m above partners

    max rightning moment  ca 3400 kpm

    FoS 3... preferred mast break/bend strength ca  10000kpm

    Now.. the mast..... 

    When I use the tables in “practical junk rig”, we’re looking at a mast with a breaking strength of 19000 kpm hollow Douglas mast. Diameter 31 cm at partners. Hard and probably very expensive to make..

    I would prefer a aluminium mast and have been looking long and hard at the Nedal pole as used on various other vessels

    When calculating the strength of this alu mast (220 mm/5 mm Nedal) on a vessel like Tystie I find the bending strength to be quite low. Approx 3100 kpm.... barely the same as the max rm for a boat like Tystie.. or for the HFJY34 for that matter

    Are my calculations way off? 


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    Last modified: 09 Feb 2019 12:53 | Anonymous member
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