Newbie here – I’m hoping that your experience can explain the events of a few days ago and at least offer up an explanation as to why this occurred. I cannot portray how this event scared me, but here's the story.I’m out in my Catalina 27 for the second time this Friday between Noank, CT and Fisher Island in Long Island Sound. It’s a beautiful day with winds 5-10kts, seas 1 foot, mid-80s under a partly cloudy sky. We’re sailing along on a starboard tack, maybe a little slow at 3-4knts, and decide to come-about. We execute the tack and as soon as we complete the tack, the boat starts to turn back to port. We spin 360 degrees and stop dead. I ask why she turned back to port and my friend replies that she didn’t turn the boat back.So there we sit in 40 feet of water, wind crossing our port side, boat positioned on a beam reach, mainsail full of wind, headsail tight with wind, and our knot meter reading zero. We were perfectly still and remained that way for 5 minutes as we tried to think our way through. There was nothing in sight to be caught on. We were in the proper position on our chart and confirmed with GPS. The boat was NOT rocking with the waves, which struck me as odd. I started the engine and attempted to motor ahead with little luck. Finally at full throttle (11hp inboard) we made it to 1kt. Desperate, I decided to turn the boat around and head back east for no specific reason except for that was the way home. As we started the turn the boat suddenly started to spin uncontrollably, we quickly spun three times in a perfect circle to the point where we were both thrown down into the cockpit. I counter steered against our direction and just as suddenly the boat stopped. We were facing east, I throttled the engine at full speed and we motored away.Afterwards there were no ill effects. The engine operated normally, the rudder/steerage was fine. My friend insisted we continue to sail and everything went fine.Thoughts? Please help me to understand what may have occurred because it truly scared me. Could I have been caught in a rip tide/under current that was perfectly balanced with the wind? Is there a novice error that I made? Thanks for your help.