I thought this forum dead as received no email advising responses until yesterday with
JessicaLovely has just replied to a thread you have subscribed to titled - Barnacle removal without scraping - in the Construction, Maintenance & Refit forum of Cruisers & Sailing Forums.
But nowhere can i find it.
Anyway not it is not near the batteries but along th whole hull so I bit the bullet and gave up environmental concerns to cut back below water line before coating with epoxy and then antifouling. A loal shipewright said he had noticed this marking on boats in last couple of years.