Club Skipper is the club's own sign-off rather than an RYA qualification, and holding it is what lets a member take a club yacht out as skipper, with a crew of their own.
There are four levels, and they set how far you may take a boat: Club Day Skipper within the Solent, Club Coastal Skipper from Anvil Point to Selsey Bill and round the Island, Club Yachtmaster Coastal up to 20 miles from a safe haven, and Club Yachtmaster Offshore up to 60.
Each level asks for the matching RYA certificate, logged sea time on club boats with several different skippers, night hours, a radio licence and first aid, the endorsement of two club skippers, and one practical Skipper Check with an instructor. You sit the check once; after that you move up as you qualify.
The full requirements are in the Sailing Orders, and building your miles sets out the route from a Day Skipper ticket to taking a boat out yourself.
If you are working out where to start, the club has just circulated a guide, “Sailing skills and qualifications development in SOYC”, which lives in the RYA course guidance folder of the documents section on the booking site. It is the clearest statement of how the grades, the RYA courses and the sea time fit together.