Houseboats

Just a couple of weeks ago I was on a houseboat in southern India. This weekend I was walking around another houseboat on the north Norfolk coast, near Brancaster Staithe.

This one is simply a metal hull barge with a long shed on top.

Quite a nice shed, as sheds go - and I like sheds - but this houseboat, presently stuck in low tide mud, couldn't go anywhere without a tug, as it has no propulsion. An earlier version with a timber hull lies adrift and rotting in the background.
So, anyone suggest its purpose? Could it be a base for mussel farmers? They take the shellfish from nearby mussel beds and transplant them in local creeks, to be harvested again once they've reached maturity. Do fishing boats tow them to the site? It can't be for leisure purposes as no-one I know would fancy a week in a shed on mudflats. But wait - isn't that what twitchers do? Surely it can't be a hide for observers of wading birds?
Answers on a postcard please ....