Aluminium sail track welded to mast

[nik36]

Hi all,
I have a 10m mast which will carry a 20m2 mainsail. I intend to tig weld the sail track to the mast but so far have been unable to find an example regarding weld size and spacing. I can understand the 100s of rivets/screws closely spaced normally used because rivets do pull out, but I was considering every 200mm, maybe that's a bit too far apart. It's a balance between overwelding and the track lifting as the sail pull on it.


Any examples/advice appreciated.

[Manateeman]

I TIG weld a lot on my aluminum vessel...we have a TIG onboard. I would not weld the track on a spar.
M

[nik36]

Originally Posted by Manateeman

I TIG weld a lot on my aluminum vessel...we have a TIG onboard. I would not weld the track on a spar.
M

Are there particular reasons you wouldn't?

My greatest concern is structural. The mast is a 150mm diameter 3.3mm thickness tube of a weldable alloy. The track is 25mmx6mm internal and about 3mm thick.



Key concerns:
(1) Will it distort the track internally too much for the slides.
(2) Will the track lift and bend under load if the welds are too far apart (fatigue issues).
(3) Will it weaken the mast (more than screws anyway)
(4) Will I survive the tedium of all those small welds 8-)


The advantage to me is that currently everything else on the mast is welded, no dissimilar metals at all. The mast can also be made watertight (giant float).The mast is new and laying on the floor of my workshop so cleanliness and access is not a problem.

[JPA Cate]

You're kidding yourself about making the mast a float, because you need to have sheaves for halyards topping lifts, and the like, and both require slots cut into the mast. Water will come in.

Fwiw, our mast track is held on with s/s screws that have been treated with anti-seize. The anti-seize really does work, but you do have to use it.

Ann

[Bean Counter]

Potential problem I see, is if the track gets damaged such that it causes jams on the cars, then de-welding/cutting as opposed to drilling out a few rivets and replacing a section of track may be a headache, especially at sea.

[RaymondR]

Assuming you are talking about slot welding, which is filling the holes in the track with weld, It should not cause a problem. The heat affected area of each hole is fairly minimal and would probably cause less damage to the parent metal than drilling lots of holes through it.

You'd probably get by with 200 spacing towards the top but I'd tend to reduce the spacing towards the bottom and at the bottom where reefing loads are going to put a lot of horizontal load on the track, no more than 100 mm apart and maybe even 80 mm.

I broke my boom a few months ago. The proximal cause was a crack which had developed from where the SS fitting for the vang had been riveted in using SS rivets so I'm not keen on dissimilar metals on alloy spars at the moment.

My old boat had the mast on a pedestal and none of the halyards ran out through the side. It would have been easy to run the halyards down through conduit and seal the ends with expanding foam.

[Manateeman]

Well, I’m kinda concerned because I think even if you are very careful about heat, you are talking about just one side of this tube and I’d run over this idea with an engineer. Maybe post it on boatdesign net.
I would think anyone would need a lot more information on the spar, shape, what kind of track. The thickness of all everything. What series aluminum.
I’ve never seen anyone do this and I’m not sure there is any advantage over fastenings. Could you please post more info, drawings...anything else on moms, spreaders, the rig, the boat...what else has been welded, where and what else might be attached to the spar.
I’m not sure anyone can help without a lot more info.
Happy trails to you
Mark and his Miller beer, MillerTIG ,Milling aimlessly looped Manatees.

[adjo]

The mast is probably 6061 T6 which is a "heat treatable" alloy. Welding partially anneals it. I would avoid doing this to a mast.
The Differences Between Heat-Treatable and Non-Heat-Treatable Aluminum Alloys

[StoneCrab]

While non of engineering comments are technically incorrect, I doubt the mast is that highly engineered for strength, stress and weight. Once the standing rigging is on it, the mast is mostly in compression.

On the fly maintenance repairs aside, if rivets can hold the track on, tack welding will surely hold it since there will be much much more metal in the tack than in the rivet.

[nik36]

Originally Posted by adjo

The mast is probably 6061 T6 which is a "heat treatable" alloy. Welding partially anneals it. I would avoid doing this to a mast.
The Differences Between Heat-Treatable and Non-Heat-Treatable Aluminum Alloys

The alloy is 6060 T5. Thanks for the link. I'm thinking that a partial anneal may not be such a bad thing if it is confined to a series of small welds. This may also help avoid stress concentrations that would occur with holes.

[nik36]

The track comes without holes, so I'm thinking of welding on the outside. It's a fairly industrial type extrusion, fairly thick so I'm not to worried about distortion on the inside from the welds outside. I think the spacing you suggest makes sense.



The crack in your boom may have been partially the hole and not corrosion, can't tell without looking. Stress concentrations are scary. I worked for a place with 40m towers to support a grain elevator - got some funny looks when I suggested to the electricians that they'd better call for an engineer before drilling holes in the columns for their conduit brackets.



I make/repair a lot of bullbars (although our bulls tend to hop). The ones that are just made out of 50mm tube tend to crack at any hole , even small ones (usually added by someone for an antenna bracket) when hit. Where there are no holes they will crack (at greater force) at a MIG weld and where I tig weld them they don't crack (probably the partial annealing effect).

[nik36]

I agree, the mast should be in compression (hopefully all the time). Because I only had access to industrial type extrusions my mast is actually slightly greater diameter than with a "proper" mast extrusion. I based my calculations on a very similar timber boat that had a mast 140 x110mm and my mast is 150mm diameter. The total mass is very similar. From memory the stiffness goes up by something like the square of the diameter so I should have quite a bit of excess which covers any loss by welding.

[nik36]

Originally Posted by Bean Counter

Potential problem I see, is if the track gets damaged such that it causes jams on the cars, then de-welding/cutting as opposed to drilling out a few rivets and replacing a section of track may be a headache, especially at sea.

I hadn't thought about repairs at sea. Presuming I could wait for a calm moment I could easily cut the welds with a milling cutter in an angle grinder, not as easy as drilling true. Then I guess I would have to rivet the repair section to the mast.


If the whole track becomes worn over time, I could just weld another one on top (at least the first time) and if that had to be removed it would be easier to cut because it is spaced above the mast material itself.

[nik36]

I've never had much luck with engineers, not because they are not clever, but because they don't like to give casual advice on small and unusual matters. Usually they want to have a formal agreement with a fee so they can pay their insurance companies in case they get sued. In a way it's sad because they have so much skill and knowledge and they can't apply it because people can't afford it.



Many years ago I new an engineer who was doing some mathematical modeling on the melting of a solid material for his Phd. This was just as computers went from text to graphics. He was interpreting his results from a printout of numbers summarized as a series of lines through his "solid". As a favor I did a false color cross section and noticed that parts of his "solid" where melting from the inside out - probably a local space/time warp. I think that got buried and he got his Phd. Lost track of him but maybe he is designing those 4th generation nuclear reactors now

[billgewater]

Look at spars that come out of professional spar shops. Do they ever weld the tracks on? I must say I have never seen welded tracks on a mast .... ever.

There must be some reason(s).

I believe that being conservative with boating practices is probably the best path to follow, unless you are into experimenting which can be horrifically expensive.