Welcome to the Maunie of Ardwall blog

This is the blog of Maunie of Ardwall. After a six-year adventure sailing from Dartmouth to Australia, we are now back in Britain.

Tuesday, 22 January 2013

Sacrificial Anodes, Bilge Ratting and Mosquitos

Photos, above: Sacrificial Anode before and after one season; the hot and sweaty 'King Bilge Rat gets the holding tank out
Sorry, with all the maintenance work going on, the last blog had a few technical boaty terms which maybe should be explained. The Sacrificial Zinc Anodes are important bits of kit which protect our expensive feathering propeller (when we are sailing, the prop's blades fold back to reduce drag). If you did O Level / GCSE Chemistry you will remember the Periodic Table of Elements and perhaps the Galvanic Table. Basically if two dissimilar metals are connected in an electrolyte solution (such as sea water) the one at the anodic end of the Galvanic Table will corrode and the one at the cathodic end will be protected. Our propeller is made of a bronze alloy and is fitted on to a stainless steel shaft so the propeller would corrode and the stainless steel would be ok. So a zinc anode bolted to the back of the prop will take all the corrosion leaving both the shaft and prop protected. As you can see from the photo, it corrodes quite quickly , particularly in warm water, so it's really important to replace it before it losing its protective powers.
Anyway, Chemistry lesson over, we are still in a hot boatyard, waiting for Franc the Welder to finish our solar panel frame. Unfortunately the proximity to a large mangrove swamp makes the place a mecca for mosquitos and, despite liberal sprays of repellent, burning mosi-coils and rigging mosquito nets, the little buggers are getting us. The only consolation is that we've bought a zapper, which looks like a plastic tennis racquet and has 2 AA batteries in the handle. There's a definite sense of delight when a forehand drive sees the mosquito burst into flames on the electric wires but the score of 'kills' vs 'bites' is still stacked in the mosquitoes' favour.
Whilst we have been waiting for Franc we have continued with other jobs that we have been putting off. Graham has been doing some advanced Bilge Ratting, having discovered that the toilet holding tank has a small leak when in use (not A Good Thing). Bilge Ratting is the term for crawling into confined spaces in the bilges (below the floors) to access hard-to-reach bits of kit and he's quite good at it, even though he's the wrong size; the perfect boat engineer is 4ft tall with 6ft long arms. So yesterday, in very hot temperatures he climbed into the cockpit locker, disassembled the shelf, disconnected and removed the central heating system and then discovered that the offending tank was built in to the boat in a way that removal would not be easy. Unfortunately the builders, Northshore, have made quite a habit of this with Maunie so we keep finding things that are almost impossible to reach, which is fine until they go wrong. Anyway, after an hour with a hacksaw blade cutting through fibreglasss, he managed to slide the tank out and, having removed the cockpit lid, it came out into the evening light with millimetres to spare. This was truly extreme Bilge Ratting and he deserved the honoured title of 'King Bilge Rat for his efforts.
As darkness fell, we lowered the tank to the ground and Graham opened up the access hatch and cleaned it out with a not-quite-long-enough-handled brush (this unpleasant job became known known as 'going through the motion's ) so a hot shower and a cold cider were very welcome after it was done. Close inspection in daylight this morning showed five pin holes in the stainless steel plate and some corrosion in one of the welds (another chemistry moment here – stainless steel will actually corrode if there is no oxygen present, so where it rested on its base there was a airless trap which allowed corrosion to take place). One of Francs' men has taken it into the workshop to weld it up and make it watertight again – it's not delaying the main job as apparently they have just realised that they don't have enough tubing of the right diameter to build the legs of the solar panel frame . Aaaaaaarg! We're staying remarkable calm – must go and kill a few more mosquitos!

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