The ship seen keyside is Insperation Hornblower and she is a Catamaran yacht/ferry. There's not a lot of information available on the vessels specs but good chance she's constructed in line with WPC Fast Craft so she would be built mostly from aluminium. Aluminium hulls have advantage of being very light and still structurally strong BUT they don't react well to being on fire so vessels of this type have extensive fire protection built in. Engine rooms(on a cat there'll be 2, one in each hull) would be like armoured boxes, deckheads and bulkheads from vehicle/cargo deck up to cabin areas most likely S60 rated(designed to contain fire up to 60mins) and certain hatches and access points would also be S60 or S30 rated. If it turned out the ship they featured as their cruise ship is built to those so of specs, there's a better reason for struggling to get signal rather than void spaces and they wouldn't have had to make it up. Void spaces btw are a thing but they'd be down in the hulls below the cargo deck level.