Alkali corrosion.

[cal66]

Help please with a worrying problem.I am getting serious disintegration of the wood in my bilge where the hull anode is bolted.This has been happening now for many months and takes the form of grey crystal deposits with a mass of matted wood- fibres.The crystals are slippy with wet fingers which seem to indicate an alkali.I have washed off these deposits but they reappear.I have also disconnected the anode cable to the stern- gear but this makes no difference.There is a bolt through the hull which seems to be the centre of the problem area,could it be that this bolt is in contact with the anode and is causing a battery effect?
I have had extremely useful advice in the past from forum members and I thank you in advance if you can help.
Doug Callaway-South of France

 

[Seanick]

Try rinsing with a strong hot vinegar/water solution to netralise the alkalis.

Remove the anode and stud at the next opportunity, make good/scarph in new timber and ditch the anode.

Fit a shaft anode instead.

If you think you really must have an anode, redrill for the stud about 4mm oversize, tape up the hole from the outside, epoxy fill, warm resin only. When cured, redrill down the centre of the hole, and epoxy coat the plank inside and out in way of the anode only.
This helps insulate the timber from the alkali salt which cause delignifcation of the timber.

 

[Peterduck]

I concur with Seanick's observations. Not all boats require anodes, so try doing without and keep a close watch on your metals, eg propeller,to see if there is any degradation going on. The business of electrolysis on boats is a terribly frought one, and generally not well understood. I have even had "experts" in the field give me conflicting opinions.
Peter.

 

[LittleShip]

I also agree with Seanick................. I use heat shrink on all my through hull bolts to help prevent this problem. That said I have one through hull that is having the bonding system taken off this year due to your problem.

Wood boat ........... who'd have em! /forums/images/graemlins/ooo.gif

Tom

 

[cal66]

Sounds like good advice will implement as soon as possible.Thanks again