HFJY34

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  • 11 Feb 2019 02:16
    Reply # 7157082 on 7156352
    Anonymous wrote:

    Taking the maximum rightning moment of the boat as starting point of the mast calculations  makes the most sense to me.  Times 3 as safety factor. Eric Sponberg does the same.

    Then again... what about the mizzen mast....


    Sponberg's article on designing free standing masts:

    https://www.ericwsponberg.com/wp-content/uploads/design-engineering-masts.pdf

    Last modified: 11 Feb 2019 02:21 | Anonymous member
  • 10 Feb 2019 15:24
    Reply # 7156352 on 7155071

    Taking the maximum rightning moment of the boat as starting point of the mast calculations  makes the most sense to me.  Times 3 as safety factor. Eric Sponberg does the same.

    Then again... what about the mizzen mast....


    Last modified: 10 Feb 2019 15:24 | Anonymous member
  • 10 Feb 2019 13:07
    Reply # 7156219 on 7155556
    Anonymous member (Administrator)
    Anonymous wrote:

    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...



     I picked the strength of spruce from Ian Nicholson's Boat Data Book.

    There were three numbers to pick from, tearing force, crushing force and breaking force. Not knowing what to choose, I picked the 'weakest' one, the crushing force at 45MPa. If I had chosen 71MPa instead, then the breaking moment would rise from 11600kpm to around 18500. I have later looked up data about wood, and my 45MPa are most probably on the low side. However, I have just used local trees for masts, not knowing how good quality they were, so I my thinking was 'Better safe than sorry'...

    Arne

    PS:
    As early as in 2006, I had a go on finding the strength of wooden masts. I have later 'refined' the way to guess the righting moment of the boat, but apart from that, the write-up still makes some sense, hopefully. 
    The uncertain factor is the strength of the wood material.

    Last modified: 10 Feb 2019 13:37 | Anonymous member (Administrator)
  • 10 Feb 2019 08:34
    Reply # 7156107 on 7155071

    Hi David. 

    We have thought about the schooner rig for quite some time.

    In the end I went with the yawl version hoping/thinking better performance and cheaper to build. 

    An early version of the schooner looks also very nice...

    Last modified: 10 Feb 2019 08:39 | Anonymous member
  • 10 Feb 2019 08:22
    Reply # 7156104 on 7155071

    Hi Annie. I haven't decided yet whether to go ahead with the build or not. There are a couple of things that need to fall in place. I want to be able to finish in four years and my budget would be around 35 k euros.. So before I jump in I want to be sure that it can be done within my limits.

    So far she's staked out in the garden..


    Last modified: 10 Feb 2019 08:26 | Anonymous member
  • 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
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