When buildings give root territory, capturing them shouldn't be too easy (so that the buildings connected to that territory don't switch ownership too easily/quickly/often).
Every building with that property, besides the Carthaginian naval shipyard, therefore have a significant garrisoned capture regeneration rate (or disable capturing, like monuments).
Since the model of this building doesn't appear to have a lot of space for units to garrison (5), nor a lot of defensive capabilities, it should be still easier to capture than a civic center or fortress (20).
Therefore it seems reasonable to increase the capture rate inherited from general special structures and keep it below that of a civic center.
The british crannog is also 'super dock' which gives root territory, but it is a civic center and not really a shipyard, so that doesn't appear to need tuning.