Closing halyard exit slots in aluminum masts

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

  1. Manateeman
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    Manateeman Junior Member

    Greetings all. I would appreciate comments and wish these would stay on subject. There would appear to be four major opinions. First, ignore them . Second, fill or patch them. Three, TIG weld, Four, internal and external plates with rivets.
    We have asked several mast builders and have had several divergent solutions as answers. We have read pages of opinions as to the correct rivets. Some of the TIG welders feel strongly that given the new generation of inverter based machines, the heat affected zone can be minimized and thus TIG welding offers the strongest option.
    My particular concern is old halyard exits near the partners on keel stepped mast. One very qualified NA recommended an inside aluminum plate riveted using the existing four holes...then TIG welding a slot filling plate the size, shape and thickness of the slotted area. He added a wrap of biaxial glass in epoxy above and below the mast partners if I was concerned about crushing in this area.
    Looking forward to advice.
    Kindest regards, Mark Manatee
     
  2. gonzo
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    gonzo Senior Member

    What is the reason to plug them, cosmetic?
     
  3. Ad Hoc
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    Ad Hoc Naval Architect

    Would help if you provide the "subject" of your enquiry.
     
  4. Manateeman
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    Manateeman Junior Member

    I am converting a deck stepped mast to a keel stepped. Most of the old halyard exit holes would now be below the deck partners, but one is above and close to the deck. My question is how best to retain the most total mast strength.
     
  5. bajansailor
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    bajansailor Marine Surveyor

    Are you intending on having the new halyards outside the mast, or will you have to cut new exit holes for them to suit?
    If they are going to stay in the mast, would it be possible to keep the exit hole (referred to above) close to the cabin top, and then take the halyard to a block on the deck and thence to (eg) a self tailing winch on the coachroof?
     
  6. Manateeman
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    Manateeman Junior Member

    Thank you for the reply. Yes, we will cut new halyard slots. And yes, we think exactly along the same lines with regard to the slot near the deck...down to a Block and up to a winch. I’ll post the distances...it’s tight but probably will work.
    I’m concerned about the forces of the mast against the partners given the slots that exist. The slots are 1 x 3 inches.
    The center line of the opening below the deck is only 9 inches lower than the deck. On the opposite side of the spar,
    the opening is 6 inches above the top of the mast deck collar. The mast is 10 x 7 , 3/16 wall. It was a Pacific Spar.
    The top is tapered and masts steps welded to the top.
    We know the newer generation of Miller inverter based TIG welders can truly keep the heat to a minimum. I have not seen a lot written on the idea of an internal backing plate and a welded closure plate. Any references would be appreciated.
    Again, thank you. Mark
     
  7. gonzo
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    gonzo Senior Member

    Is this a mast from a different boat, or are you shortening the mast on an existing boat?
     
  8. bajansailor
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    bajansailor Marine Surveyor

    I am thinking that you are perhaps worrying unnecessarily here about the existing apertures / openings in the mast (?).
    It sounds like they are not going to be in way of the mast partners (you mention that one is 6" above the deck collar, and the other is 9" below the deck).
    And the mast is obviously strong enough re buckling from compression loads, otherwise it would have failed by now.
    If the rig is set up right then there shouldn't be any huge sideways loadings on the mast from the partners while sailing, unlike an unstayed rig where the mast is a long cantilever. And you have the full cross section area of the mast in way of the partners.
     
  9. Barry
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    Barry Senior Member

    It is important to know the alloy and post treatment before you think about welding onto the mast. My comments are not all inclusive but simplified to make a point

    Assuming that it is 6061-T6
    6061 being the alloy mix, and the -T6 the treatment after to enhance strength and other characteristics

    6061T6 shows a yield strength of about 35,000 psi, the stress at which the aluminum will bend permanently -T6, solution quenched, artificially aged to get its high strength
    6061 -0 shows a yield strength of about 12,000 psi, -0 no additional heat treatment, hardening or aging (except naturally ) processes

    If you heat the T6 it will revert somewhat to the -0 yield strength, ie lose yield strength

    When the tig arc melts the T6 aluminum, an area around the weld that sees an increase of heat will lose strength. The HAZ, heat affected zone. From 35,000 psi to a minimum of 12,000

    So the question is " Will the decrease in strength as the T6 alloy reverts somewhat to the -0 designation result in a mast weaker than just leaving the holes as they are?

    You mention the Miller inverter welders. Our shop was blue. Irrespective of the type of machine that creates the tig arc you still need to reach about 1200 F to melt the aluminum to create a weld. The only way that you could limit the HAZ is to use extremely short welds and air cool between the beads.

    The problem with TIG is that it takes a bit of time to start the melting process which does create a large HAZ before the filler can be applied. It has been our experience
    that a MIG will create less distortion as the weld starts immediately without the preheat of the tig arc. So if I was to weld in filler pieces, I would use short MIG stitches, and air
    cool between the weld.
    Additionally tig welding is slow in say inches per minute creating even a larger HAZ

    BUT I would leave the existing holes as they are as it is my OPINION, that by MIG or certainly TIG, that you will lose more strength than just leaving the slots as they
    are.

    So leave it as a T6 high strength mast, 35,000 psi with slots rather than a larger area HAZ -0 temper 12,000 psi strength area without the slot.
     
    Last edited: Nov 14, 2019
    bajansailor likes this.
  10. Manateeman
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    Manateeman Junior Member

    This is a used mast which was deck stepped at one time. I’m not sure if it 6160-t6 but I hope I will have an answer as to the alloy today and will post it. The slots are 24” apart vertically, alternating from one side of the mast to the other .
    We understand the HAZ issue but are there any tests on masts? What If we use a backing plate larger than the slot and rivet or screw it to the mast and this plate has two layers such that the outside piece fills the opening completely and would help carry some of the compression load ? A sandwich of three pieces ? Plexus rather than weld?
    One suggestion was to ace bandage round the spar with glass / epoxy and run some carbon fiber over glass up the spar and taper it so as not to create a hard spot. It’s a beautiful spar and yet the idea of leaving these big slots open frightens me. We are thinking about a bench test to crush some pipe but surely someone has computer software which could provide a better answer.
    Sincere thanks to all who replied.
    Mark
     
  11. bajansailor
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    bajansailor Marine Surveyor

    Suppose you have two identical masts, each with the same size slots in them.
    On one mast the slots have the fittings with the pulleys / blocks for taking the halyards etc.
    On the other mast the fittings have been removed, leaving holes in the mast (I presume that this is the scenario that you are thinking of?).
    Which mast will be stronger in compression?
    I am thinking that if the fittings have been removed, then you will locally have a reduction in cross section area of the mast, making this area locally weaker in compression. But if the fitting is left in place, and is securely attached (ie 'built in') then it should form part of the useful cross section area to resist compression (?).
    Hence maybe best to just leave the existing fittings in place, rather than mess around with them?
    If you are worried about appearance, maybe just glue a very thin fascia panel over the fitting? You wouldn't even have to rivet it - glue should be sufficient (?).
     
  12. Manateeman
    Joined: Oct 2019
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    Manateeman Junior Member

    Hi. Thanks for the reply. The existing fittings are just stainless halyard exit plates which have 4 holes in the corners. They were held in by 1/8” aluminum rivets. Not a lot of strength there in compression. I removed the exit plates, the winch
    pads, two or three welded mast steps and some storm track and the boom attachment casting. Very , very little corrosion, just paint blisters.
    The mast was coated with zinc chromate and then painted. The mast heel, the spreaders and the cap are all in terrific shape. Pacific Spars built a very high quality mast.
    Please let me describe my current thinking on the halyard holes. We would make a backing plate for inside the spar , a bit larger than the original stainless plate. We would clean out the edges of the hole and the inside of the mast near the holes.
    We would hold this by either rivets or threaded screws. Next, we would make a plate which would fill the opening as tightly as possible. This would be the equivalent of the mast wall in thickness and shape and alloy thus taking some vertical load without creating a hard spot. At this point I’m not sure what I will do. TIG weld it carefully ? Plexus?
    Now it becomes complex. Should we have fabricated a exterior plate so that the mast wall becomes the meat in a sandwich? Should we just butter it up and paint or do we wrap the whole section in triaxial in epoxy...and add some vertical stiffening . At this point, I’m lost. I just cringe thinking about the huge slots. Yes...we know about the HAZ zone issue. Very carefully welded, perhaps...perhaps...an internal and carefully fitted filler piece could restore the compressive strength of the spar. I’m open to discussion . Again thank you all...kindest regards, Mark
     
  13. gonzo
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    gonzo Senior Member

    A simple solution would be to add a sleeve of aluminum over the whole area. You can set in epoxy or an elastomer like 5200.
     
  14. Manateeman
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    Manateeman Junior Member

    Hi. Gonzo. Thank you for the suggestion. Well first, I think it would be very difficult to fabricate an overlay in aluminum because we don’t have an existing similar extrusion from which most builders construct sleeves. I assume you mean something like the sleeve used to join 40’ mast extrusions only on the outside. It is a very interesting suggestion and we did look at this option. A lot of folks do not realize sleeve splicing a spar is very common whenever the extrusions exceed 40 feet. I’ve seen some done on keel stepped spars at the spreaders and between the deck and the boom. On line, there are examples of zig zag tapers to avoid a hard spot. Your suggestion is similar to the idea of wrapping the spar with triaxial with our without verticals in carbon fiber over glass. I’m not sure about 5200 but one can find an epoxy with suitable strength and flex elongation. Your idea is quite similar to the glass/epoxy wrap that was suggested to us by a naval architect for whom I have a great deal of respect.
    There have been discussions on line suggesting an epoxy / aluminum bond would at some point fail. Others point to the aircraft industry where a combination of rivets and adhesives are used with great success.
    I’d like to try to strengthen these openings with the minimal amount of structure. A more elegant approach which might be useful to close off halyard slots with the mast in place. We also thought about a welded support similar to the way Reckmann builds spars. At this point we are waiting for the answer as to the alloy which Pacific Spars used to construct this spar. In the end there might be several solutions which would work.
    Again, thank you and kindest regards.
    Mark
     

  15. Ad Hoc
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    Ad Hoc Naval Architect

    Well, as already noted above, the strength is already there, since it has not failed yet!

    Fully concur.

    I would not recommend welding it to cover this aperture.


    Yes, as this is what Gonzo also notes, is far preferable. However, this is not so easy to give full recommendations, in the absence of pictures and dwgs of the exact set up.
    However, I would strongly advise against carbon fibre. It will eat the ally.

    It "sounds like" all you really what to do, is cover an unwanted/unsightly hole up....yes?
     
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