Dissimilar Metals

When two different metals meet if the circumstances are right then one will generously pass itself over to the other which may or may not be what you want. If it is in a cheap battery then yes this is a reaction you need to effect a flow of electricity but if it is two bits of metal on a boat then usually this is not a desirable outcome.

The problem on a boat is that it is hard to avoid having different metals together in some places – stanchion posts are usually steel, their bases may be steel or aluminium and the toe rail those are attached to is often aluminium. And the circumstances are always going to be right as sea water is salty so conducts electricity quite well. The result can be unattractive bubbles of corrosion or it can have more serious consequences such as where a steel fitting like a radar bracket is attached to an aluminium mast. The new pulpit required two replacement stanchion bases and these have been manufactured locally from stainless steel rather than the original aluminium for speed, time and cost reasons. This has moved the risk of galvanic corrosion (the correct term for the process) from between base and post to base and toerail. However corrosion can easily be prevented by using a suitable barrier, in this case a thin plastic pad between the two metal parts.

Corroded windless base

Meanwhile as Kevin moved the anchor chain around so that the pulpit could be fitted he discovered some unwelcome galvanic corrosion has started between the steel plate that the anchor windless sits on and the anchor windless itself. A mass of bubbling metal at one corner of the aluminium windlass case where it bolts to the plate indicated that the aluminium was leaving the windless for the steel plate. If allowed to continue the corrosion would weaken a strong point that Temptress might rely on if we were anchored in severe weather so needed urgent treatment. To that end all 70 odd metres of the main chain plus the warp and chain we use for our second anchor had to be removed from the anchor locker to ease access to the fixing bolts. The chain and warp are now laid in tidy lengths on the pontoon alongside the anchor and been given a good hose down for the first time in several years.

Will he get out of there?

Windless, plate and messy shelf

The steel plate just needed a clean up

The anchor well also contained a fair amount of rotting seaweed, rubbish dropped by the metal workers when tailoring the pulpit (the boat hook helped remove a marker pen before unloading the chain) and mystery stuff like bits of the manufacturers label from the anchor which you think would be washed over the side not down into the well, two halves of a chain link actually lost in the depths by the skipper when he replaced the swivel that joins the anchor to the chain earlier this year and other odds and ends. Most rinsed out easily with a hose as the two cowls on the outside of the drain holes were knocked off by the towing bridle (one of the repair jobs waiting to be done under the insurance claim) only the heavy items remain, probably indefinitely. The well being like an upside down pyramid about chest deep is hard to get in and out of  and it is impossible once in, to bend or squat down to pick up stuff from its small floor space (I know I’ve tried). A possible need for one of those litter picking thingies or else we have to simply ignore the remaining rubbish.

A day or so later Kevin threaded himself feet first into the well, the only way to undo the bolts that hold the anchor windless and its steel plate in place. Both I and passers by wondered if he’d get out again but he did. Then the forepeak had to be partially emptied of sails so that the windless could be disconnected from its power supply as the cables aren’t long enough to otherwise lift it onto the deck from its shelf at the rear of the anchor well. Meanwhile the rough weather lashing the coast resulted in the water supply to the pontoon being cut due to wave damage so fresh water to wash everything down with was in short supply. Having scrubbed away the dirt with bucketfuls of sea water the final rinse was water from the galley tap. The weather was decidedly flaky – apart from strong southerly winds which have been tossing water over the marina wall for the last couple of days, intermittent rain showers coated red Sahara dust on everything. And, when it wasn’t raining, you were breathing in that same thick dust leading to coughing and sneezing fits or a perpetual runny nose, working outside had become particularly unpleasant.

What to use as insulation? LanoCote, a sort of lanolin grease often used to protect against corrosion, had been smeared on when the steel plate was replaced a few years ago but obviously hadn’t stood up to the wear and tear of the anchor chain rattling past or all the salt water that washes into the anchor locker when at sea. As mentioned plastic is an ideal inert insulator. We recently bought a couple of 50x70cm sheets of 1mm thick translucent pink plastic in the local ferreteria as part of our ongoing mosquito screen project (more on that when it is complete). Ferreteria Tias (or FT) is a veritable Aladdins Cave of DIY materials and kitchen equipment that we have both become addicted to. Kevin re-purposed a 20x20cm piece of the lurid plastic to become a sandwich filling between the winch and its steel mounting plate. It is easily cut with scissors or a knife and can be drawn on with a biro or pencil.

Plastic cut and ready to go

 Meanwhile opening up the electrical side of things has enabled him to check on and clean  the down switch that had caused us problems when anchoring in Essaouira over a month ago. Something to pass the time between dry spells! And, as its still raining and rapidly getting dark, the whole lot can wait until tomorrow to be reassembled.