Hi, The surveyor who inspected my boat mentioned a priority replacement of
the "fuel tank flame gauze" in his report, but I have been unable to find
out what he was referring to. The marina where my boat is isn't familiar
with that term either.


That's a term commonly used in the UK.
In fact, if your boat is propelled by a "petrol" engine, you're apparetnly
required (in the UK) to have a gauze around the fill and vent lines.

I think this is a sort of flame retarding material, something like (but surely
not) asbestos.

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7.1.2 A vessel should be provided with a fuel tank of sufficient capacity for
the main engines, and its area of operation. All fuel tanks vents should be
fitted with a flame gauze as required by BS/EN/ISO 10088, and carried to at or
above tank filling plate level and where there should be no danger from
escaping fuel or vapour.

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From:

http://www.mcga.gov.uk/c4mca/mcga-gu...-guidance___re
gulations-inland/dqs_iw_code/dqs_machinery_petrol_code.htm