I'm local - there is no slipway along the East Sussex coast other than Rye to the far east or Newhaven to the west.
Or use Sovereign lift in/out but that's expensive and not sure if they let them in anyway.
Most jetskiers use the beaches closer to the sailing club between the Redoubt and Princes Park.
Best thing is to make contact with them and share the load when launching.
Any winches on the ES beaches are owned by sailing/fishing clubs or local (professional) trawlers.
Obviously you need to work with the tides and have the right trailer/wheels for the pebble/shingle/sand/mud mix we have here.
Sorry I cannot help more, not a jetskiiers - can't stand the things, PITA.