After completing the Day Skipper shorebased and learning all about mooring and allowing extra rope length for a falling tide, I didn't.
Spent to long talking to a pal at his office at Pwllheli Marina and when returned to the rib found the starboard tube about 3 feet above the water and the whole rig looking very uneven. After efforts in pulling the rope to get thr rib higher to unclip and pass the rope back through the handgrip I gave up and reverted to the knife. The tubes scrapped down the wall and eventually the rib levelled out.
Always remember to allow for the tide, I will - or take a big knife.