SURVEY & CORROSION
Q The folding prop on my Ocean Bird trimaran is protected by a zinc anode. Unfortunately, the anode failed (oops, fell off!).
When I beached the boat for a scrub-off, I replaced the anode. Shock horror, I also discovered the prop had started to change colour!
My question is, how can I tell if this is just surface discolouration and the prop is basically sound, or must the prop be replaced because it’s now likely to fall to pieces?
Colin Brown replies:
Dezincification is usually a gradual process so the short-term loss of an anode may not be too serious.
You could try polishing your propeller to see if the discolouration is removed and if the metal below is sound and not pitted or soft. Use a wire brush or fine sandpaper with water. Be very careful about any dust you make and wear a mask while you work. If you get bright yellow metal you’re good to go but if the prop has suffered from serious dezincification, the metal will be dull in colour and in extreme cases it may well be soft enough that you can break bits off the blade edges with a thumb nail or a light hammer. The exposed metal faces would then be distinctly pink (see photo above).
