PBO reader Maureen Owens is unsure how to protect a bronze prop shaft bracket, our paint and antifouling expert has this advice...
Maureen Owens from Gosport asks: “The bronze prop shaft bracket on my boat regularly seems to foul up but I’m unsure what to use to coat it with antifouling.
“Am I right in thinking a copper-based antifouling product would not be a good idea on a bronze fitting?”
PBO paint and antifouling expert Richard Jerram replies: “Any fittings below the waterline are going to attract fouling like shell and weed in the same way as it attaches itself to your hull.
“And you’re right – in order to avoid galvanic corrosion of metal fittings below the waterline – particularly aluminium – it’s best to avoid coating them with antifouling paint containing copper.
“Galvanic corrosion, also known as bimetallic corrosion, occurs when two dissimilar metals are electrically connected with each other via an electrolyte (in our case, seawater).
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“Whichever metal is lower down the galvanic scale will corrode. That’s why we attach zinc anodes to our boats – the zinc will corrode first, leaving other metals free from trouble.
“Trilux 33 is a copper-free antifouling and is available in a 375ml unit and various colours so would be an ideal product for antifouling bronze fittings. I’d recommend you apply three coats after first cleaning and abrading the bracket.
“Prime the bracket first with a minimum two coats of Primocon underwater primer. The same Trilux 33 can also be applied to your boat propeller if required.”
Got a question? Email pbo@futurenet.com and one of our experts can help.