They are for tensioning running backstays on a gaff rigged boat.
The backstay on the side the boom is out is disconnected and let loose on a rope tie. When going about, the windward one is hooked back to the lever and the lever 'over centered' to tension it up. The stay runs through a block on the deck before being hooked up to the sliding part.
On the upper one you can make out Laurent Giles - well known designer who "invented" them (or at least popularised them) in the 1930s, mainly for his racing designs which had lofty rigs that needed every bit of support available when going to wind. Those may have been, as suggested off a gaff rigged boat given the rather crude hooks. Valuable bits of kit to the right person.