Esper Refit 31 – shaft crevice corrosion

Bad news this week as we inspect our shaft, which has some corrosion. We turn to Vyv Cox of Coxengineering to find out how and why this has happened. Meanwhile we attempt to offer the swimming platform up to the transom, only to find it is a little too big.

Weekly Video Round-Up

No clips of Jamie burning himself this week but do check out our new deck shower. We also find some corrosion in the shaft and discover that the swimming platform doesn’t quite ‘fit’.

Swimming Platform

This is our swimming platform. Big, isn’t it?

Of course this is partly the aspect taken from a wide-angle lens, and also the fact it has not been cut to size. It seems the template used to draw up the wooden decking did not take into account the thickness of the steel tube, so we’re bending it inwards slightly in order to fit the transom.

Shaft Crevice Corrosion

After removing the Maxprop we took the shaft out, only to find what looks like electrolysis.

After posting this photograph up on the YBW Practical Boat Owner forum we received a comprehensive reply from Vyv Cox, of Coxengineering. He explained that this is ‘crevice corrosion. His website gives a full explanation with plenty of pictures demonstrating how common this problem is.

As Vyv explains:

Many metals that rely on a passive film for their corrosion resistance suffer from the dual problems of pitting and crevice corrosion, stainless steels being just one example. If a crevice, such as is formed in bolted joints, swaged fittings or nuts and bolts, is immersed in water, the oxygen content of the ‘stagnant’ water deep inside the crevice is lower than that of the fully aerated water on the outside. This difference causes the metal within the crevice to become active, corroding preferentially due to the fact that the active and passive metals have different galvanic potentials. Pits are themselves small-scale crevices, as is the surface roughness in drawn rigging wire, accounting for the rust stains that can develop on them.

Needless to say we have ordered a new shaft. It should be interesting to see how easily the Maxprop shaft comes off and, more importantly, how easy it will be to put back on… in the right order.

Shower and Tap Plumbing

On a more positive note, Moo and I installed the deck shower in the rear starboard deck box (sorry, I forgot to take a photograph). The plumbing runs across the lazarette ceiling, down the lazarette wall and follows the exhaust into the rear cabin, where I’ll be fitting t-bars to the original Acorn pipes. We’re using 15mm Hep2o pipes, which are easy to work with. It’s a push and fit system.

I’ve also started to plumb in the rear heads tap. A hole had to be drilled through the composite marble, which took Pong an entire afternoon to complete, such is the density of this material! Here’s a shot of the tap in situ but without the shower attachment. When fitted, the shower attachment retracts into the tap to operate as a normal tap. Pull it out and you’ve got an instant shower… or an Asian bidet!

Ceiling Completion

Bar a few bits and pieces the ceiling is now complete. We’ll be taking it all down again in order to fit the deck fittings (and also to take the lights down in order to back them with aluminium plates) but not before grabbing a shot of saloon ceiling in all its glory.

Boom and Mast Fittings Completed

Having finished the main mast last week we finished fitting the mizzen, the booms and the spinnaker pole. One of the mouse-lines had disappeared in the main boom and upon closer inspection I found what appeared to be a bird (or mouse) nest!

Liz Returns To The UK – With A Baby Blakes Toilet Seat!

Now that we’re down to one toilet, we thought we’d clean up the Baby Blakes toilet seat on the spare. It is Liz’s turn to return to the UK so she’ll be ebaying the seat when she gets home. If you’re interested in buying it (and for the uninitiated, a new seat cost £600!), please get in touch.

What’s Next?

Deck fittings! Gotta get on with them. Now that the ceiling is almost complete, we can take them all down and start drilling holes through the deck.

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