Angle of vanishing stability

We had a bit of a reality check today when we hired a 20ft Hunter from the Low wood water sports centre. The sun was shining and fluffy clouds scurried high above Lake Windermere. The wind speed indicator on the website that we had logged into earlier was reading 18 to 21 mph, so it seemed to us that we had booked ourselves a fun day to try out our new found sailing skills. We had hired this boat a couple of months ago and so felt confident that we would know what we were doing, it would be familiar. What wasn't familiar were the conditions once we were out on the lake.
We met the previous hirers leaving the jetty and casually asked how it was out there. Exciting, came the reply, you just need to back the jib when your tacking. Oh, er OK, we both nodded, not wanting to appear ignorant, but we actually didn't have a clue what he meant by that.
We didn't get off to the best of starts. As we reversed away from the jetty the engine cut out and we drifted towards the launch ramp and ran aground. We had to be pulled off by the centre rescue boat, and then we discovered that the fuel line was detached from the engine, which is why after 10 seconds it had failed. Not exactly our fault then, but we should have noticed that, or maybe we should have waited for a member of staff before we so confidently set sail.

Once out on the lake it was apparent that today was a very challenging day to be sailing, even on a lake. We struggled with the lines, the jib sheets being fouled by a mooring line that we had not noticed was tangled and should have been tided before we left the safety of the marina. I teetered nervously for'rd on a wildly swaying deck as the wind caught our tiny craft with Jackie at the helm trying to tame the beast and head her into the wind. That problem solved we set about trying to cope, as best we could with the battering we were getting. All our best efforts were leading us into more and more precarious situations as the boat heeled ominously, and our ability to keep her on an even keeled were making us both very anxious indeed. We were discovering that we knew very little indeed about sailing. This fundamental knowledge was obviously lacking from our Parthenon of Day skipper practical and theory courses which we had passed with flying colours.
After about three quarters of an hour battling to sail anywhere, Jackie made the call. We don't know what were doing and we both feel decidedly nervous and just a little scared.
We drop the Main sail, let the jib flap about and start the engine to head back for the marina. By now we're both soaked with spray as we beat back against the waves to try and get this bouncing boat back to safety.
We limp into port, struggling, even with the outboard which is difficult to manoeuvre with the wind gusting at 20 odd knots as we drift towards the man waiting at the jetty to take our lines.
We feel very embarrassed, and somewhat stupid, but we have learned a big lesson, and that is, that we don't know how to sail. We might know how to identify a cardinal bouy, how to plot a course, how to read a chart, how to tie a clove hitch, but we don't know how to set and trim our sails so as not to pass that angle of vanishing stability. Luckily we didn't capsize, but I think we came pretty close, and it was scary.
Maybe it's different on bigger boats but it has taught us that we still have a way to before we can be confident sailors. We need to know how to sail.