HFJY34

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  • 10 Feb 2019 07:58
    Reply # 7156102 on 7155071

    Here's another sketch from Chris Morejohn of a 34ft boat with a junk schooner rig

    This puts the foremast into the space ahead of the double berth, rather than through it. With a schooner rig, similar to the 34ft Benford dories, it gets much easier to find or make masts. What's the thinking behind putting most of the sail area into one large sail, Frederik? I found 54sq m a bit much to handle, which is why I went back to a ketch rig.

  • 10 Feb 2019 02:55
    Reply # 7155872 on 7155071

    It's great to see another new boat about to be built!  I shall be following this with interest, Frederik.  I dare say your progress will be more rapid than mine!

  • 09 Feb 2019 21:44
    Reply # 7155556 on 7155071

    Thanks for the replies.

    Arne. 

    Are you using modulus of rupture in your calculations? For a 310/62 mm hollow spruce that would be 72 Mpa with a breaking strength of approx. 16300 kpm...

    If I was aiming for a minimum of 10000 kpm, then a hollow Spruce pole 260/120 mm diameter with 60 mm thickness would be enough..?  Weighing in at ca 140 kg.  Theoretically...

    Another possibility might be making a hybrid mast consisting of a 8 meter  alu 6082t6 pole, 240/10 mm with a wooden 6 meter topmast (1m bury). Appr. 200 kg.. 


    Scott.

    Yeps I am happy with the design. Going back and forth the last couple of months has been very interesting. The brief was; ocean going, shallow draft, junk rig, outboard engine, two persons. Now I'm doing the rounds and finding out about materials, prices etc... we'll see..

    Last modified: 10 Feb 2019 07:24 | Anonymous member
  • 09 Feb 2019 16:38
    Reply # 7155263 on 7155071

    Tystie's 220mm dia x 5mm wall mainmast actually had a doubler inside, 3m of the same section as the mast, with a sliver cut out of it so that it could be squeezed in and persuaded inside the mast. Because of the longitudinal cut, it may have doubled the wall thickness but I don't think it doubled the strength of the mast, though it must have added something.

    The original LAP was 10.5m, for a low AR rig, so somewhat shorter than this proposed design. When I lengthened it for a high AR rig, it was with a 10in dia x 0.25in wall tube.

  • 09 Feb 2019 16:19
    Reply # 7155255 on 7155071

    Frederrik,

    I am excited to see you are considering building a Chris Morejohn HF design with a junk rig. I absolutely love the lines on all his drawings. I had a few email exchanges with Chris but eventually it became clear that boat building was not the way for me to go right now. I share your opinion. If I ever build a boat the HF designs will be right at the top of the list.

    I would very much like to see the HFJY34 drawings from your post brought to life and sailing.

    Last modified: 09 Feb 2019 16:25 | Anonymous member
  • 09 Feb 2019 16:13
    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
    Message # 7155071

    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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