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Old 26-07-2010, 14:56   #1
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Hairline Crack on Aluminum Mast

Hi I have an old steel 43 ft boat with an aluminum mast of unknown name. The mast is a 43 ft (13 meters) in length. At the base of the mast there is a crack in star port and a larger one in port side of the mast. I could post pictures. Is there any way to fix the mast without spending more money than the boat is worth? I heard welding aluminum is out of the picture. And second does anyone know the factory for this mast? The boat is a 1978 - 13m Finot Reve Des Tropique (DREAM OF THE TROPICS)
Naval Architect: Jean-Marie Finot.
Thanks in advance.
George
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Old 26-07-2010, 15:07   #2
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As it's deck stepped the cracks have to be fixed. Why is welding out of the picture? I have an aluminum mast that is tapered. The taper is welded.
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Old 26-07-2010, 15:08   #3
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Looks like just a few inches. I would shorten the mast. Cut it cleanly above the cracks, then reinstall the base plate with fresh rivets. Off you go...
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Old 26-07-2010, 16:10   #4
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Aluminum is welded all the time
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Old 26-07-2010, 17:10   #5
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Quote:
Originally Posted by cburger View Post
Aluminum is welded all the time
I think the key here is the cause of the crack. It was not sailing stress, it was was expansion stress caused by corrosion between the step casting and the mast. Perhaps motion contributed, but this is not like a crack up by the spreaders, which would be very difficult to repair.

Clean it up and weld it. If the rigging shop isn't interested or is over priced, and sheet metal shop or metal fabricator will do it... if you can get it to them!

And put an anti-corrosion compound between the mast and the step!
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Old 26-07-2010, 17:14   #6
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There seem to be rivetts. Remove the plug in the foot of the mast and either fit a longer one well beyond the cracks, or get it welded by someone who has samples ofhis ally welding to hand. This is also the time to lengthen or shoten your masr, replace all wiring and fit LED nav lights etc.
Do a full and detailed inspection on the rst of it too. A good welder will have dye-penetrant inspection materials. You smear the material with liquid that creeps into cracks, then wipe dry and spray with a powder coating that stains in contact with the liquid.
This should also be done around the new welds after cleaning up just to be sure they have no defects. This isn't a job you want to do again next year!
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Old 26-07-2010, 17:46   #7
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I don’t think there is much there to weld on the bottom several inches. The corrosion has thinned the aluminum and the buildup has stretched it apart. You don’t weld on corroded aluminum.

Pull the base out of the mast and inspect. (Figure out a way to submerge in vinegar for a day or so, this will cause less damage when you pull it apart.) The base plate will have some severe corrosion too.

There are several possible fixes and none too serious in time or money. You could shorten the mast past the corroded part. You may have to replace the base and that would get expensive, as it would have to be fabricated. If it is just slightly pitted it could be cleaned and the pits filled with epoxy it the corrosion is not structural but more of a cosmetic nature.

I would secure the foot plate with something more substantial than pop rivets, though I know that in theory they don’t really hold anything other than keeps the base in the mast until such time as the rigging puts tension on the foot of the mast.

You could have a sleeve wrapped around the lower 10-12 inches of the mast and welded on. This seems to me to be a good idea no matter what as the base of the mast would then be much stronger and the whole thing would take much more corrosion before becoming structurally degraded. And don’t think you can stop the corrosion, you can only slow it down.

None of this is beyond a decent welding shop.

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Old 26-07-2010, 20:13   #8
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Cut the cancer out (off). There are only a couple reasons not to do so - boom clearance over a pilot house or your head in the cockpit. Standing rig and a cockpit Bimini can be shortened by a few inches if need be, with a hacksaw at virtually no cost, if you've the skill to go it alone.

Band Aids on this are just that, Band Aids. There is no permanent jury rig....
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Old 26-07-2010, 20:34   #9
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OK, cleaned out the cat box and put dinner on the stove (ick, yes, washed my hands!) and thought about this. Still recommend the cancer be cut out of the spar. Also recommend someone GOOD look at it. How old is the boat? Is this metal fatigue, or, is the rig tuned too tight? Have you been through hard winds? Cut the cancer out, find the cause, eliminate it if you can.
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Old 26-07-2010, 21:02   #10
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I concur with everything Um-Suadade said, and in addition I would add a weep hole in the base in a location that would allow rain water to drain instead of building up. May prolong the interval between the next corrosion repair for quite a while........
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Old 26-07-2010, 21:46   #11
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Mi2ndwind:

I forgot to add that part. This all started when the bottom of the mast did not drain. A good wake up call for everybody and sometimes not so easy to get to with keel stepped masts.

Actually a good bet is to wash the inside of the mast with fresh water if the boat has been drenched in salt water in rugged conditions.(and make sure it drains!)

US
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Old 27-07-2010, 00:58   #12
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Hairline crack on mast

Thank you all for all the good ideas.
Does anyone know where I could order a raised step as suggested that I could rivet the mast on plus a collar for extra safety? (The piece must be able to be shipped to Cyprus in the med where the boat is on dry dock!)
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Old 27-07-2010, 14:02   #13
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Assuming you are also on Cyprus so you can actually interview some local fabricators, you might want to try some yacht repair yards or some welding fabricators who are familiar with aluminum.

I would think the least expensive and most praactical (strong) repair would be to cut off the bad part of the base, 4 to 6 inches? And then remove the "key" that was set in to the mast to hold it in the deck step. Then reinstall that "key" in the base of the mast, and raise the deck step itself by putting a 4 to 6 inch thick plate (block) under it, through-bolting the deck step to the extension and through the cabin top, with a reinfocring plate under it. That should be as strong as the original and require minimal custom work, just making the holes in the block and giving it a suitable shape so it isn't ugly.

The block could be any suitable material, ultra-high-density polythene (UHDPE), or metal alloy, or a block of fiberglass, even aa suitable wood block. If you find a fabricator who is comfortable with the job they will probably make the choice based on what is locally available. No "collar" would be needed in that arrangement, since th original mast would still be keyed in the original mast step, and the block under that would be held by compression as well as by the longer bolts.
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Old 27-07-2010, 16:10   #14
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G'Day 3000,

Seems to me that the first thing to do is get the "plug" out of the mast so that you can see just how badly corroded the extrusion really is. Aluminium corrosion products expand remarkably, and it may be that there is enough meat left in the extrusion to simply weld up the cracks and reinstall on the existing base. Possibly small local patches welded over the crack area for reinforcement rather than an expensive fabricated sleeve would be useful.

Hope that you can find a competant welder nearby!

Good luck with it all

Jim
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Old 27-07-2010, 16:54   #15
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By the way, if the local welding shops turn their noses up at Aluminum and say it can't be done?

Check out the local airports, aviation shops work on aluminum all the time AND they usually have better skills. When their welds fail, it winds up on the local news, so they try just a little bit harder.
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