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Freshwater sailer

Aluminium Fin Repair to Trailable Yacht

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Hi all,

I was recently given an old 22' Trialable yacht, more sports boat than cruiser .   Not sure what type, but I think largely home made (by a boat builder, so a semi professional job).

Mast, hull sails all in reasonable condition,  they do need a lot of work but easily fixable with some hard work

The retractable Centerboard is solid aluminum, around 5' long with a small lead bulb, I am told around 600 pounds.  The centerboard is around 1 1/2' thick and 18' across, so quite solid.   It appears to have been milled from a single piece into a foil shape.

However at some point in the boats history it has been left in the water with the centerboard retracted, and there is now heavy corrosion just above the bulb.  Around 20% of the thickness of the aluminum centerboard has corroded away on the full circumference of the board, but only over a height of around 1/2', effectively a corroded 'slot' around the full perimeter of the Centreboard just above the bulb.   With 20% of material gone from each side around 50-60% of the original thickness remains.  The balance of the Aluminum above the corrosion is in excellent condition.

The boat will be kept in the water for around 6 months of the year, and I intend epoxy treating the aluminum to prevent any further problems in the future.

My concern is repairing the corrosion/loss of strength in the Centerboard.  The obvious thing to do is to remove the bulb,   clean the corroded slot up and have it professionally filled with weld.

I would like to avoid what I suspect will be a substantial cost of getting a new Centerboard milled

Will this work?   Any other ideas?

The quality of my Newbie images will depend on the quality of your response........

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The only thing that makes this thread less scary is the size of the boat.  Google "Excalibur capsize"

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What does the welder say about the repair adding any strength to it?

 

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How about cutting the bulb off then trimming the corrosion off and re attaching the bulb.  Yeah you will lose some kept depth, which will also result in loss of righting moment.  But might be the thriftiest option.  Not sure what aluminum welding and filling does for the strength of the metal...

 

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What alloy is the aluminum??  This is a crucial piece of info. Weld fill might actually weaken the joint depending on the alloy & treatment.

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Can you just remove the corrosion, and fair down the foil in a smooth taper to the bulb? There may be no need to weld it if enough material is left. Only certain aluminum alloys are weldable, so that may not be an option depending on the alloy. E.G  the 70xx series have zinc in them, high strength when cast and machined, poor corrosion resistance, non weldable. 

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I’m a bit confused with your use of the ‘ diacritical mark to indicate both feet and inches (is the issue half an inch in size or half a foot in size?), but is it possible that what has happened is actually electrolytical corrosion between the lead and aluminum?

If that is the case and 40% of the material is already gone, then the entire corroded area is Swiss cheese. Cut it off - and install significant zinc protection when you remount the bulb. Epoxy protection alone will not be enough as every chip will be a corrosion magnet.

And how is the lead attached to the aluminum?

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