Lofrans Airon windlass - corrosion

[jwilson]

I have a Lofrans Airon 1000 watt electric windlass, fitted new in winter 2004/5. The windlass itself works perfectly, except that the aluminium warping drum above the gypsy is corroding. The rate of corrosion seems to be increasing rapidly over the past year. It it keyed onto a stainless steel shaft above a chain gypsy of what looks like some kind of greyish metal. The gypsy and shaft are fine. An image showing the drum and the corrosion is at http://www.yachtsnet.co.uk/lofrans-airon.jpg

About 15 months ago I asked the UK Lofrans importer (Peachment), if they could get me a replacement drum. I was told that neither they nor the factory in Italy had any spares, but that they had had several other customers enquiring for the same spare part, and that Lofrans were arranging to get a batch of spares made up.

On following this up this week Peachment have now told me that there appears no realistic chance of getting spares, and that the drum on the Airon was different from those on current models for which spares were available.

I am thus contemplating the best way to have made up a replacement drum. Turning/casting aluminium or Tufnol/Delrin or replicating in glass-filled resin? I am also wondering if anyone else needs this particular spare part - maybe getting a small run of them made up to share costs.

 

[Adamastor]

The drums are die - cast ali, which was usually anodised. Looking at the issue you have, I'd check the electrics, because there are signs of what may be electrolysis, I'd say.
You will be horrified at the cost of machining a lump of ali bar to make a new drum, because of the keyway etc.
I'd rather wait on Italy to make with new spares, or possibly look at getting your unit welded and then powder coated in the meantime.

 

[jwilson]

Interested in this suggestion, but I don't quite see how any battery-related currents could be flowing through the top drum other than from the fact that the alloy drum sits on a stainless spindle with only a smear of grease between them. With seawater around as an electrolyte at times this will cause some electropotential difference between the dissimilar metals, and induce corrosion in the alloy. This was my assumption for the cause of the corrosion, and why I was wondering about machined Delrin/acetal or moulded glass-filled resin as a replacement drum as an alternative to alloy. I've been waiting 15 months for a new drum already..... If I ever replace the whole windlass guess what make it won't be ?

I will check though for any voltage with power on between either the + or - battery feeds to the motor and the drum/spindle though next time I go on the boat, also with power off any resistance path between the same points.

 

[vyv_cox]

I agree, I think you are looking at galvanic corrosion in which the warping drum is trying to protect the gypsy. Presumably the two are in fairly close proximity and water bridges the two? The only palliatives I can suggest are to increase the clearance so that water cannot remain there, or introduce a plastic washer of some sort. I think I would try filing a couple of millimetres off the skirt all round to see if that works

 

[jwilson]

I agree, I think you are looking at galvanic corrosion in which the warping drum is trying to protect the gypsy. Presumably the two are in fairly close proximity and water bridges the two? The only palliatives I can suggest are to increase the clearance so that water cannot remain there, or introduce a plastic washer of some sort. I think I would try filing a couple of millimetres off the skirt all round to see if that works

There is as standard a plastic washer between drum and gypsy, but I think that salty water often bridges the connection: that makes sense as it is the base where the large plastic washer sits that corrodes most. I don't think I can take much if any off the base of the drum as the clutch mechanism relies on pushing the drum down into contact with the gypsy and pressing that down onto a cone clutch.