a little off topic, but while the chat is ventilation here goes,
just after the introduction of the bss on the broads i booked an inspection with a recommended examiner,
he arrived at my boat rather well dressed and carrying a briefcase which he laid on the saloon table, took out a clipboard with a load of paperwork, a tape measure, slide rule and a calculator, he then put on a boilersuit took the slide rule and measured every slot in 7 louvre vents, every gap under each door then every opening window, put all his findings into the calculator and after an hour told me the ventilation on my boat was within guide lines. the full inspection took almost 3 hours
a couple of years later he landed a high ranking job at the broads authority. the mind boggles