Mooring problem... lines are getting tangled.

[Tollerowner]

I have a Precision P15K that I have kept moored for about 6 years.  I have a swivel about a foot below my buoy.  The buoy has the chain going through it to a shackle.  Then I have three lines going to cleats on either side of the boat and the bow eye. 
Until this year everything has been fine, but now the 3 lines are getting twisted around each other.  What's worse, I have metal thimbles inside the eyes  and they are rubbing against the other lines and damaging them.  As I said, the prior 3 years nothing twisted and nothing got damaged.
I sailed yesterday, and today the 3 lines are twisted.  I thought perhaps the boat was rotating around the buoy, but not much has happened since yesterday.

Any idea what is going on?
Do I need the thimbles?  Without them, at least the lines wouldn't be damaging each other.
Would it help to replace the shackle with another swivel?

Any advice would be appreciated.

[Jeff G.]

   I always used a bridle, each end on the front cleats and a line from the bow eye. The bridle was the primary. Bow line was a little longer with a float on it.  With it being stiff do to the pool noodle, it kind of acts like a stand off from the buoy and a backup line if the bridle would fail.

[Spot]

At school on the sailboats, we run a line spliced to the center cleat through a bow cleat, through the loop on the mooring, back through the other bow cleat and then cleated off to the center cleat. This is working in wind and tide. I cannot comment on what is going on for swivels, etc. but I could ask.