Closing halyard exit slots in aluminum masts

Discussion in 'Boat Design' started by Manateeman, Nov 12, 2019.

  1. Barry
    Joined: Mar 2002
    Posts: 1,136
    Likes: 78, Points: 48, Legacy Rep: 158

    Barry Senior Member

    I wrote rigid to restrict entering into a discussion on highly elastic material or material able to creep at reasonably ambient conditions
    An in depth or complete discussion of STATIC strength of materials is beyond a reply to a short thread so I have taken liberties to keep it simple
     
  2. Barry
    Joined: Mar 2002
    Posts: 1,136
    Likes: 78, Points: 48, Legacy Rep: 158

    Barry Senior Member

    The question you should ask yourself is that when you compress say a block of aluminum would the failure line be 90 degrees to the
    compressive force. And/ or when you bend a piece of material, simple bending, with a simple cross section that the shear flow is in the direction as the tensile and compressive stresses, or rather along the same axis as comp and tension stresses. Shear flow in beams. Plus if compression and tension ultimate stresses are the same then a constant cross sectional beam would some times fail in compression as well as tension.
    I have never seen a compression fracture. Shear failure or tension failure only

    It is extremely important to note that failure due to a compressive force does not mean that the material has reached some kind of ultimate compressive stress which you allude that it is the same as ultimate tensile stress. Rather that the compressive force introduces either bending stresses in a slender member which fails when the tensile yield occurs or in thick members will normally fail when ultimate shear stresses are reached
     
    Last edited: Nov 20, 2019
  3. Ad Hoc
    Joined: Oct 2008
    Posts: 6,124
    Likes: 358, Points: 83, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    I think there is a slight mix and matching of terms and misunderstanding between them going on.

    The term rigid that you used, i read as, and I am sure you meant as being 'stiff' or not flexible. Which in the case of a solid block is correct.

    But this:
    Im not sure 100% it aids, just leaving it as "rigid" is sufficient on its own, as it is understood by any engineer.

    You're getting confused between Ductile and Brittle and its relevance in this discussion.

    Ductile just means that there is a lot of plastic deformation, i.e. stretching, of the material prior to failure.
    Brittle is the opposite, there is little or no plastic deformation prior to failure.

    It is just a mechanism of failure and related to its material proprieties and any geometric constraints on said material, or in this context, structural arrangement.

    Aluminium for example, does not fail in a brittle manner.
    It does not mean it cannot, as under exceptional circumstances it can occur in 2000 and 7000 series alloys owing to the alloying elements at the HAZ. But this is microscopic brittle failure between alloying elements which is far removed from brittle failure owing to the material proprieties that can be easily seen looking at the fractured surface with the naked eye.

    Just to follow on from Barry's comment above.
    In general, most welded joints failure in shear, very rarely tension or compression. The asymmetrical loads placed on the joint invariably create conditions of pure shear in the weldment.
     
  4. gonzo
    Joined: Aug 2002
    Posts: 13,609
    Likes: 382, Points: 93, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    Yes, it does mean that the material reached the ultimate compression strength, which in the case of aluminum is the same as tensile. Do a little research on materials and you will see.
     
  5. gonzo
    Joined: Aug 2002
    Posts: 13,609
    Likes: 382, Points: 93, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    What do you mean by STATIC strength?
     
  6. Manateeman
    Joined: Oct 2019
    Posts: 31
    Likes: 1, Points: 8
    Location: St. Mary’s Georgia

    Manateeman Junior Member

    Greetings all. Well since the subject of welding aluminum and that the idea the Heat Affected Zone in my 1 x3 inch slots would somehow significantly weaken my mast, I would like to put forward the following idea.
    I would construct an interior backing plate for the slot, a bit larger than the opening. Use the existing four corner holes to rivet the interior backing plate in place. Construct a filler cookie and TIG weld it in place. The backing plate and the cookie will be the same thickness as the mast. Obviously I’d clean the mast interior and keep the weld heat as low as possible.
    I thought about using rivets and plexus but I look at all the mast steps, all the heat and filler and what... am I going to start worrying about these very much smaller welds ?
    I had a good friend with a 60’ sports fishing machine, a very strong boat with a very high tuna tower. Three good sized guys up top. Boat slamming into very decent seas, wide open throttle. Sitting up top is amazing. Just TIG welded anodized pipe. Some tower builders weld through the anodized layer which means the anodized aluminum becomes incorporated into the weld. It’s a tiny amount. I’ve seen cracks but tuna towers are pretty robust. I just love to watch truly talented TIG welders control over heating the weld. I don’t believe properly filling these slots will weaken the mast.
    Again, thanks to everyone who replied.
    Mark the manatee
     
  7. Ad Hoc
    Joined: Oct 2008
    Posts: 6,124
    Likes: 358, Points: 83, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    That depends upon your definition of 'weaken' the mast.

    The mast is 'designed' to satisfy the unwelded strength of the alloy and any localised regions that are of concern and will have been addressed in the original calculations of the strength of the mast and the alloy's properties.
    However:

    1) Welding the alloy will reduce the strength around those slots from a max possible yield strength of circa 260MPa down to circa 115MPa.
    2) In doing so locally, the strength is reduced and also the weld bead will become a localised stress raisers, which increase the stress at the weld beads, thus making it weaker for the same given load.
    3) The change in chemical composition of the alloying elements in the weld, and the way it is welded will introduce porosity, which also reduces the fatigue strength as well as introducing further small stress raisers.
    I could go on...

    There are many reasons why it is best not to weld it......all have previously been mentioned.

    But this is your choice...
     
    Last edited: Nov 22, 2019
    Barry likes this.
  8. Manateeman
    Joined: Oct 2019
    Posts: 31
    Likes: 1, Points: 8
    Location: St. Mary’s Georgia

    Manateeman Junior Member

    Hi. Ad Hoc. I am listening to your opinion which clearly is correct technically. I’m not sure about the induced prosity but I know it will not be a nuclear quality weld, but it’s a very small area.
    What if I skipped welding and used interior and exterior covering plated riveted together using the original four corner holes. Maybe with plexus or an epoxy mix.
    Are you saying just leave the slots as is ? I’m assuming you saw my drawing .
    Mark
     
  9. Ad Hoc
    Joined: Oct 2008
    Posts: 6,124
    Likes: 358, Points: 83, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    You will always get porosity with 6000 series welds.
    And whilst you're not wanting a nuclear quality weld.....on a cold dark winters night in the middle of storm in the ocean...you may be revisiting that notion!

    As noted by others too.
    Leaving it and/or adding cover plates as blanks which are adhesively fixed with epoxy is far more preferable.
     
  10. Manateeman
    Joined: Oct 2019
    Posts: 31
    Likes: 1, Points: 8
    Location: St. Mary’s Georgia

    Manateeman Junior Member

    Hi. Plates both inside and outside ? Any recommendations on epoxy? I’m thinking monel rivets...correct?
    Would you reinforce the spar in the area of the mast partners with glass in epoxy...someone suggested this.
    Again, thank you for your time. I will never forget the graciousness of the people I met in Japan.
    Sincerely, Mark
     
  11. Ad Hoc
    Joined: Oct 2008
    Posts: 6,124
    Likes: 358, Points: 83, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    If your objective is to merely cover the "unsightly holes" and prevent any ingress of water, then a cover plate and any good adhesive will suffice, sikaflex is one option.
    If you are able to apply a cover plate inside too..fine, but not 100% necessary of your primary objective as as aforementioned.
    I would avoid riveting. Since you may just pinch/nick the parent metal where you did not intend to or unable to see once riveted....so why invite trouble?
     
  12. Manateeman
    Joined: Oct 2019
    Posts: 31
    Likes: 1, Points: 8
    Location: St. Mary’s Georgia

    Manateeman Junior Member

    P
     
  13. Manateeman
    Joined: Oct 2019
    Posts: 31
    Likes: 1, Points: 8
    Location: St. Mary’s Georgia

    Manateeman Junior Member

    Thank you all. The HAZ has often been quoted in discussions on TIG welding spars. I agree that it exists. The extent to which it compromises the structural strength of a spar is the critical question. So far, no one has directed me to a test of materials which clearly indicates what welding should or should not be done.
    For example. I would guess, drilling halyard slots in the middle 50 % of a panel is not a good idea. OK. So where is the evidence welding existing halyard exit slots is s similar bad idea.
    The current Pacific Spar I have, has TIG welded mast steps up both sides. Thus, was it built with no regard to the structural loss from HAS.
    I just don’t see the definitive testing or examples of mast failure based on heat affected zone.
    Bad welding, careless welder preparation...this I can believe, but to say on a dark and stormy night, I will regret welding?
    That is fear mongering . Good grief, my whole boat is welded aluminum LOL.
    No one has commented on how to wrap an ace bandage of glass in epoxy around the spar where it is clearly stressed at the deck. Excuse me, but I’m not sure how to calculate the loss of strength from two halyard slots very close to the deck.
    Three point fixity certainly means this area is significant.
    Please let me restate. I have no desire to have a carbon fiber mast. A powerful 75’ mast is not what I consider a prudent mariner would entertain for higher latitude sailing with older owners. Apologies to Ted Brewer and all the young.
    I have a perfectly fine turbo diesel to go to windward.
    Please. Let us stick to proven testing, sound examples and lastly open discussion. I had also hoped to see some new thoughts with regard to wishbones although personally, I need to get sailing sooner.
    Again, my sincere appreciation to all. We may not agree, but it is a pleasure to listen.
    Kindest regards, Mark the manatee.
     
  14. gonzo
    Joined: Aug 2002
    Posts: 13,609
    Likes: 382, Points: 93, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    Is there no spar maker of metal fabricator that can make a sleeve for the mast?
     

  15. Manateeman
    Joined: Oct 2019
    Posts: 31
    Likes: 1, Points: 8
    Location: St. Mary’s Georgia

    Manateeman Junior Member

    Hi Gonzo. To answer your question, I assume you mean an internal aluminum sleeve similar to the type used to splice mast sections. The answer is yes. We have access to the equipment required to bend plate up to 12’. We can TIG weld them the same way Rondal spars constructs masts. Creating fingers would spread the stresses as this is a common technique used to splice mast extrusions.
    We also had a recommendation from a naval architect to simply wrap the section in glass in epoxy and feather the laminates above the deck level. I know this suggestion will open a Pandora’s box on the subject of sticking glass to aluminum as well as a debate on epoxy. So I will set this subject aside for the moment.
    Both cures to my aluminum mouse holes would add weight and would create a more rigid section...might not truly matter.
    Both are a lot of work when a far simpler “TIG cookie” might do just as well.
    We understand TIG welding creates a weak spot in 6000 series, but all I’m asking at this point is for more data on experiments or examples which prove any TIG welding on aluminum spars is a very bad idea. Certainly someone must have seen or tested such weld failures in spars. As a boat builder, I learn a lot from my mistakes.
    Again, thanks for all replies. A most excellent forum.
    Mark the manatee
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.