Empty crows nest?

Land ho! off the starboard bow. Took myself off from Largs to island of Great Cumbrae on this fine sunny day....hadn't spotted this black metal "crows nest" with its ladder access on the ferry before must make enquiries...excuse is I usually head up top but feared the gusting wind might whip me into the briny today

Extra is on slipway once known before car ferries as the "tattie pier" when
puffers called to collect Ayrshire potato 'exports' for which the island was famed