Had a Rival 34 moored fore-and-aft on the Tamar last year, with two 20mm new lines each end, and each chafe-sheathed.
I inspected closely ( and kept an 'insurance log' ) each time I visited, and found that flakes of rust from the summer-new galvanised hard eyes were chewing into the lines where the splice-loop divided and was seized to the eye.
That's when I put on an additional 'loose' chain wound around a car tyre 'snubber'. Inelegant - but effective. The boat was then going nowhere without my prior approval.
I used chain on a drying mooring for many years and found it better than rope because the weight helped her dry out in the right place and much more certain it would not foul up when slack. I told a local scrap dealer and an engineering insurance inspector that I would buy 1/2" chain for cash and soon had enough in the garage to replace the mooring when it wore. Normal steel chain is as good as stainless as it generally falis by wear not corrosion. May still have some chain under the bench somewhere. Definately recommend chain for moorings.
However careful we are, chafe will always find a way to outwit us. Padded chain is good, but regular, careful inspection is the key.
I've had swing moorings for the last 19 years and, so far, no failures. Out here, riser of about 30mm rope, shackled to maybe 6m of 3/4" chain just off the bottom via a swivel is the norm. All failures have been either worn chain or failed shackles, never the rope riser.
I have always used chain on my cobra 750. On the 12th september 2011
it was blowing F8 and gusting well into F9, six month old 10mm tested chain from a reputable supplier snapped. boat was total loss. Use biggest and best chain your boat will take
chain was back up, 16mm rope went first
I had an exposed swinging mooring in Portsmouth Harbour for ten years, often keeping a yacht on it 12 months of the year.
I found the most effective reliable connection from the boat to the buoy was a single piece of rope.
Chain caused snatching and wore things quickly.
Backups caused tangles, as the boat always rotated on the mooring in the same direction.
Obviously relying on a single failure point, you have to do something that worked. I found I could splice a strop from 32mm 3 strand and it would last over 2 years, once I had eliminated all the chafe points. That's for a 39ft boat about 7 tonnes all up.
2 inadequate fixtures are never as good as one adequate one!
My point is moorings work differently in different locations, you have to do something that works where it has to work.
Whatever you do, check it frequently, it's quite easy to think you have done a good job, only to find unexpected wear after just a day or two. One of my early efforts, the first thing that failed was the backup chain! (I think the rope wore the mousing off the shackle and the pin worked out)
I'm not advocating a single rope for everyone, just pointing out some of the issues, hope it helps?
I use two pieces of rope that come through fairleads and onto side cleats (one port and one starboard) of equal length and a slightly longer chain covered in fire hose which comes through the bow roller.
The rope should take the strain first which provides a bit of elasticity, the second rope will back up the first and if both of those fail then hopefully the chain will take on the job until someone notices