Another write up by Arne Kverneland

  • 17 Sep 2018 14:09
    Reply # 6672689 on 869421
    Anonymous member (Administrator)


    An engineer’s job is to make use of the scientists’ basic data and formulas, and try to make useful rule of thumbs out of their information  -  plus from practical experience. This lets them later design things much faster than if they had do go into 'deep science mode' all the time. I can imagine, when real new ground has to be gained (like when building the Concord SST) that scientists and engineers had to work hand in hand. We are not there with our junkrigs...

    Engineers often get it right, but it has happened that bridges, houses, aeroplanes and even sailboats’ masts have fallen down because the formulas and rules have been stretched too far.

    Still, I feel confident that my home-made mast joint rule is conservative enough to be safe. Thanks to Graeme K, who did that testing of epoxy on aluminium, I am sure the mast will not suddenly ‘go telescopic’, even with no screws or bolts added.

    Cheers, (..and cheers and good luck to Mark...)



    Last modified: 17 Sep 2018 18:08 | Anonymous member (Administrator)
  • 17 Sep 2018 13:42
    Reply # 6672681 on 869421

    Arne, great guide, just what is needed,  I will sit down with a whisky one night to have a go at the calculations!

    Tusen takk. 

  • 17 Sep 2018 11:50
    Reply # 6672561 on 869421

    Thanks, that makes sense.  I wasn't expecting "high science" but really what gave you a feel that this was the right amount.  Unfortunately I'm no engineer, so I was quite nervous designing my mast. 

    I'm trying to think what the failure modes are.  What I can come up with is:

    (1) topmast breaking/deforming at the top of the main mast

    (2) topmast trying to pivot around the top of the main, and deforming the main in the area of your lower GRP belt (heel of the topmast pushing out the alloy tube of the main)

    (3) topmast trying to pivot around its base, and deforming the top rim of the main mast, effectively ripping apart the alloy tube

    (4) differential flexing between top and main, leading to failure of the glued joint

    Any other failure modes? 

    I think the PJR formula is against (1), as the partners are assumed to be solid and immovable.  I think I was more worried about (3) and (4).  One reason I chose to have a close-fitting topmast, glued the entire length of the overlap, was to try to make them as much as possible behave as a single, solid unit.  (Another reason was that I didn't think of using GRP belts!).  I agree with you that the longer the overlap, the greater protection against all of those failures.

    Sorry if I seem to be thinking aloud at you - I'm finding it very helpful to understand what's going on with a hybrid mast!

  • 17 Sep 2018 09:20
    Reply # 6672408 on 869421
    Anonymous member (Administrator)


    there is no high science behind my suggested bury of 4-5 times the inner diameter of the lower section. Still, if we regard the top section as a balance scale with the ‘buried’ end as one arm, it is obvious that the contact forces between the upper and lower section will double each time we half the length of the bury. At some point the material, aluminium or wood, will be deformed.

    Only after I had decided on the bury of Ingeborg’s top section did I realise that this bury also would exceed 10% of the length of the top mast. I guess I will edit the write-up to say that the top section’s bury into the lower section should be.. least 5 times the inner diameter of the lower section and at least with a 10% bury...



    Last modified: 17 Sep 2018 09:20 | Anonymous member (Administrator)
  • 17 Sep 2018 08:31
    Reply # 6672302 on 869421

    Thanks, Arne, for another excellent technical guide.  I don't know about armchair reading, but it's a good breakfast table read!

    I'm interested in your guidance for the amount of bury between the topmast & main part.

    The mast for River Rat is very similar to what you describe, but I made the topmast from aluminium tube half the diameter of the main part, sheathed in wood:  

    I didn't know how much overlap to allow. My first thought was that if you regard the topmast as a mast, and the main part as a tabernacle, then I should use the PJR suggestion of at least 10%.  The length of the top part above the main part is 3m, so should be 30cm.  But I got nervous, as I wasn't sure how the forces would affect the 100mm dia tube of the main part, so went for a full 1 metre.  In hindsight, this is far too much, creating a lot of extra weight aloft.

    Your rule of thumb suggests a bury of 4-5 times the inner diameter of the lower tube.  This would give 40-50cm.  This feels about right to me.  But I'm wondering whether there's any science behind your suggestion? 

    (I should warn you I have some particularly mad mast ideas for my next conversion - but they're best kept for another thread!)


    Last modified: 17 Sep 2018 08:33 | Anonymous member
  • 16 Sep 2018 19:15
    Reply # 6671518 on 869421
    Anonymous member (Administrator)

    The Cambered Panel Junk Rig (TCPJR), Chapter 6b,
    The Hybrid Mast (aluminium-wood)

    I just uploaded a draft of Chapter 6b, The Hybrid Mast to 'my page'. I decided to make it as a separate chapter instead of adding it to the end of Chapter 6, which is about the wooden mast.

    I am afraid this is not easy armchair reading. One should be quite keen on building a mast to bother with it. No great prose, but hopefully helpful to keen wannabees. In the end, the chapter will be proof-read and any un-clear points will hopefully be put right. Have a look.


    Last modified: 16 Sep 2018 19:34 | Anonymous member (Administrator)
  • 05 Sep 2018 15:25
    Reply # 6654639 on 869421
    Anonymous member (Administrator)

    A (final?) appendix on my Fan-up Preventer (FUP) write-up

    After having played around with my FUP on my present boat, Ingeborg, and after final tests of it yesterday, I have written some illustrated notes on it and added it to the end of the FUP write-up of 2014. I think I have solved the friction problems with it. At least it works well on Ingeborg.

    If you have any comments, please jump to the Ingeborg topic as it was there the FUP was last discussed, early this year.


    Last modified: 05 Sep 2018 19:24 | Anonymous member (Administrator)
  • 14 Aug 2018 15:05
    Reply # 6572637 on 869421

    Branwen is just back in UK waters at the end of a 3 year cruise England - W Indies - Chesapeake Bay - W Indies - England. Her schooner rig has home - built cambered panel sails designed by Arne. The sails have proved satisfactory in almost all respects and are ready for further cruising.

    If I make new sails in the future, I may decide to go for a high aspect rig as advocated by David. I can see numerous advantages in his ideas, but would need to fit taller masts. So I am happy with what I have and say thank you Arne, for sharing your designs with the rest of us.

    Thanks also to David for your innovative ideas and the clever technical solutions you keep providing here.

  • 13 Aug 2018 23:00
    Reply # 6559240 on 6557913

    David wrote:But Annie, this isn't news to me! This is exactly where I am with Weaverbird. I don't know whether she's "faster" or "better" because I have nothing to compare her to. I only know for sure that I enjoy sailing her because she's fun, easy to handle and aesthetically pleasing (to me, at any rate). And if I can quote Pol, "... but WEAVERBIRD looks terrific. Very neat and totally effective." 
    Yes, David my dear, but what you don't realise is that many people reading your postings would get the impression that you think everyone should have a Weaverbird rig and that anyone who doesn't is a fool.  I know this isn't what you mean, but this is how it comes across.  Anyone who has been following your mental peregrinations will know that this is your way - I distinctly remember being texted an equally robust refutation of my feeble defence of HAR rigs when we were designing Fantail's.  Now you would be recommending one!  You are an enthusiast for your idea of the moment, which is great, but although you encourage constructive criticism and enjoy lively debate, on forum this comes across as something rather more contentious.

    You wrote the forum policies, and so I assume you consider that you are "expressing [your views] in a civil, thoughtful manner" and that you wouldn't dream of "making a personal attack", but that isn't how it always comes across.  Those of us who know you are aware of your generosity, but you do also somewhat enjoy the role of GOM, which those who don't know you may not understand.

    Arne and you have robust self-esteem.  You and Slieve have bickered contentedly for decades. But on forum these things aren't always apparent and, particularly newer members, sensitive to the trolling and bad manners that are apparently prevalent on other website, might be worried that ours is degenerating in a similar fashion.  Don't forget you are writing on the General Forum, which is open to everyone.

    If you treat as sensitive flowers having delicate egos, you won't offend.  I know that isn't your way, face to face, but fora are different, many readers use English as a second language and one does need to think before pressing Post.  I know I'm not one to talk - I tend to jump in boots and all.  Maybe this is why I am aware of the offence one can inadvertently cause.

  • 13 Aug 2018 21:58
    Reply # 6558017 on 6544319
    Anonymous wrote:
    Gary wrote:
    David wrote:

    Another way of assembling sail panels and pockets - like Arne's method, this can be done in a small room, but with a much better result.

    Actually I like that. Not sure if I could fit them to my completed sail though it could be worth a try. The webbing loops work on my sail but it's not as tidy as pockets. Am I correct that the pockets have a built in back to them David?
    No, I screw through eyelets into the batten at both ends.
    What I meant was the batten pockets are sewn up as a tube and then sewn to the sail?
       " ...there is nothing - absolutely nothing - half so much worth doing as simply messing about in junk-rigged boats" 
                                                               - the Chinese Water Rat

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