Mast steps and welding masts

Discussion in 'Boat Design' started by Bobuk25, Jan 4, 2022.

  1. Bobuk25
    Joined: Jan 2019
    Posts: 10
    Likes: 4, Points: 3
    Location: Uk

    Bobuk25 Junior Member

    Happy New Year all,

    I built a boat many years ago and after 25 years, I finally took that mast down to check it and do some modifications. The mast has worked very well, but some of the rigging was second hand when I bought it and it seemed a good point to go through things more thoroughly. As part of the work, I want to weld in steps now and remove the old British Telecom telegraph pole steps I have used all these years as I did them 60cm apart and whilst that was fine with 20 year old legs, I suspect that it will be not so fun as I get older.

    The Mast is 6082-T6, but welding in steps will weaken it in that area. Now I am not worried about weakening the compression carrying aspect of the tube as the mast can carry far more load in that area than it needs to. What worries me is the buckling issue. So I have designed and welded up some steps as below:

    [​IMG]


    I believe that this will be okay because whilst it may lose 30-50% of its strength in the Heat Affected Zone (HAZ) and that HAZ is possibly 20-30 mm from the weld centre line so weakening quite a large area of tube, I am carrying the 3/4 tube through the mast tube as a cross brace, thereby I believe making that area very resistant to buckling or kinking. I do worry about the diagonal support though as that has no corresponding brace, however the step (ladder rung over 3/4 tube) may give some support and resistance to that area too.

    What do you all think? I will admit that when I designed and built the original mast, I never did any calculations as I was 20, skint and thought 'what's the worst that could happen...' As it turned out, the mast has stood the test of time and a fair lot of incompetent sailing very well, but now I am not so care free.

    Here is the mast as it was and yes it worked well as the compression forces spread nicely and of course the poles do a lot of the work that shrouds would do on a normal mast. Whilst it is not as efficient as a normal mast, the main sail on a furling system is unobstructed by any mast pole so that claws back some efficiency:

    [​IMG]
     
  2. gonzo
    Joined: Aug 2002
    Posts: 16,925
    Likes: 1,771, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    Bobuk25 likes this.
  3. Bobuk25
    Joined: Jan 2019
    Posts: 10
    Likes: 4, Points: 3
    Location: Uk

    Bobuk25 Junior Member

    True and my old steps used stainless rivets, its just I wanted to get away from rivets and joints and go for a 'forever' solution. Basically I get worried about weak points where corrosion and such can get in and the step could fail (my fear of heights is challenging enough without fear of step breaking in 15 years time). I also have the TIG ready to go so the cost for welding is not much more than buying rivets.
     
  4. clmanges
    Joined: Jul 2008
    Posts: 583
    Likes: 147, Points: 43, Legacy Rep: 32
    Location: Ohio

    clmanges Senior Member

    I can think of another approach if you don't like rivets, but it needs a part that may have to be fabricated.

    If you can find tubing that would fit tightly on the outside of the mast (or have some rolled for you) you could make pads out of it. Weld the step onto the pad, then weld the pad onto the mast.

    I really don't understand your aversion to rivets, though. Have any of your old riveted steps broken off or become loose? If those are still sound after 25 years, then you can certainly trust new rivets for another 15.
     
    Bobuk25 likes this.
  5. rangebowdrie
    Joined: Nov 2009
    Posts: 247
    Likes: 102, Points: 43, Legacy Rep: 10
    Location: Oregon

    rangebowdrie Senior Member

    If the old rivets have gone for 25 years without adverse effects, why would you not trust new ones?
    Systems on boats seldom benefit from "forever" solutions, generally speaking, having a way to "go back" and change things prevents having "I wish I would have done this/that" moments.
     
    Bobuk25 likes this.
  6. kapnD
    Joined: Jan 2003
    Posts: 1,337
    Likes: 431, Points: 83, Legacy Rep: 40
    Location: hawaii, usa

    kapnD Senior Member

    Best to avoid welding on the mast. 25 year old aluminum that’s been exposed to salt is a poor candidate for clean, smooth welds, and anytime you blow through, you create a tremendous hot spot filling it back in, further weakening the mast.
    I’d leave it as is, and hire a fearless 20 year old to climb it!
     
    Bobuk25 likes this.
  7. Bobuk25
    Joined: Jan 2019
    Posts: 10
    Likes: 4, Points: 3
    Location: Uk

    Bobuk25 Junior Member

    Thanks everyone for replies so far, I can return to my old steps which were satisfactory if not elegant, but if I could fit the steps I have made, then it would make for a water tight mast (as water tight as it could be) and a cleaner solution. However I need it to be strong first and foremost so if that means cleaning up and putting the old steps back on, then so be it.
    My hope/belief though is that having the step tube pass through the mast tube to straddle both sides would give back any strength that the weld had taken away, but I guess to be sure I will need to find a structural engineer to do a quick analysis. Would anyone know of anyone suitable? Essentially I only need the step assembly and HAZ impact assessed because as long as the assembly is as strong as the original unmolested tube, then that is fine.

    With welding, I have already tried a bit on the old tube and it cleaned up and welded very nicely. I think this is because I am a bit fussy about cleanliness (of metal to be welded, unfortunately not of myself) and the tube is in good condition.

    Tempted by the 'hire a fearless 20 year old to climb it', but then finding a suitable 20 year old nowadays might be an issue also I am always single-handed.
     
  8. gonzo
    Joined: Aug 2002
    Posts: 16,925
    Likes: 1,771, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    If you are OK with drilling holes on the mast, the steps can be bolted on. A compression sleeve would keep the mast from deforming.
     
    Bobuk25 likes this.
  9. Ad Hoc
    Joined: Oct 2008
    Posts: 7,843
    Likes: 1,730, Points: 113, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    Bobuk25

    Notwithstanding all your caveats - which you accept - then a more 'simple' version I would recommend thus:
    upload_2022-1-5_9-0-15.png

    The doublers could be full sleeves or plate that si rolled to suit.
    This prevents penetration of the main mast - thus avoids weakening it further after the HAZ. Since cutting holes in a mast like that is not ideal, from a stress concentration point/fatigue of view.

    The only issue you need to address is that of corrosion between the two plates. Thus make sure the surfaces are clean and protected via some sealant where possible, and that the welds are 100%.
    Therefore, I'd recommend dye-pen the welds after welding to give you the confidence that there is no porosity nor LOF to allow water to ingress.
     
    Bobuk25 likes this.
  10. wet feet
    Joined: Nov 2004
    Posts: 1,498
    Likes: 472, Points: 83, Legacy Rep: 124
    Location: East Anglia,England

    wet feet Senior Member

    Aren't monel rivets the thing to use? I'm not a welder but can see the logic of the advice in post #6 .A monel rivetted solution with a dollop of Duralac where appropriate would be my choice as there wouldn't be a HAZ an you would avoid the localised weak spots. It takes a very heavy man to shear a couple of 5/32" pop rivets and obviously bigger is stronger.
     
    Bobuk25 likes this.

  11. Ilan Voyager
    Joined: May 2004
    Posts: 1,292
    Likes: 225, Points: 63, Legacy Rep: 758
    Location: Cancun Mexico

    Ilan Voyager Senior Member

    A copper nickel alloy with aluminium in marine environment is not a good idea. There are aluminium structural pop rivets that work perfectly.
     
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.