Fish Class had single pull hatches on the main deck using the Velle derricks to open. There was a locking pin that could be placed in when the hatch was closed. There was one captain, E.T. Rees who was very sceptical about the security of these hatches.
As I remember Nos 1,2 and 5 tween decks were slabs and Nos 3&4 tween decks were single pull with four sections per hatch.