I live in Hull and have been down to look at this slip a couple of times with a view to launching there if I ever get my boat back together! It's a moderately steep slip, some kind of interlocking concrete blocks laid on shingle and breaking up a bit at the edges last time I was there. If you have a 4x4 and then you should be okespecially at high tide, wouldn't like to launch there with a car though unless your boat is really light an d use a rope. Humber rescue launch their 8m (?) tornado there with a tractor, the environment agensy also use the slip with a landrover but haven't seen their boat - must be 18'+ though from looking at their trailer. Never seen anyone else down there, but there is someone on here that's launched there just can't remember who - posted some pics last year.
"I'm not lost, I'm exploring...."