Replacing mooring chain

 We have kept our sailboats on a mooring in Maple Bay for the last 5 years or so. When I bought the mooring, it had 30 feet of 1/2 inch long link chain running from heavier chain that was attached to the concrete mooring block. I had a diver inspect the mooring that year and he gave it another year before I would need to replace the chain. The next year I did so, replacing it with new galvanized 1/2 inch long link chain. Each link in this chain is 4 inches long and 2 inches wide - the half inch referring to the thickness of the metal that makes up each link. The old chain was quite wasted away in the portion that rubbed along the bottom - the rest was in pretty good shape.

Thirty feet of old 1/2 inch long link chain - not the galvanizing still left on some links at the upper end

Four years later and it was time to take a look again. The half inch chain I put down had held, for 2 1/2 years, a 26 foot (5500 lb) sailboat and for the remainder of that time, a 3500 lb 24 foot sailboat. When I snorkelled on it earlier this year after bringing our new 32 foot 15,000 lb boat to Maple Bay, I realized that the chain was clearly in need of replacement before the winter storms arrive!

As in the earlier chain, it was only the portion that had dragged along the bottom that is in really poor shape, with about half the link thickness worn away in the worst places. See the following pictures for details.

Links nearer the surface are in excellent shape after four years

These are the worst links and have lost half the metal thickness and about 3/4 of their strength

Good and bad compared

This year, I replaced the bottom 25 feet of chain (below the swivel) with new 3/4 inch chain that has twice the strength of the 1/2 inch chain and should take longer to wear out. I also buoyed the bottom 10 feet to try to reduce its wear in rubbing the bottom. I used a cluster of milk jugs to do this but this was not overly successful as they compressed with depth and do not provide enough lift. Some sort of hard shelled float would be required to make this work.

One downside of the heavier chain is the increased cost (about 35% more expensive or $10 Canadian a foot including taxes when purchased in small lengths). Another downside is its weight of more than 5 pounds per foot, which makes it harder to place. Twenty five feet was about as much as I could carry from the car to the dinghy and I should probably have used a dolly to move it. I also dropped it too far from the mooring block and had to dive and drag it along the bottom to get it into position. It was heavy to move along the bottom and took me 5 extra dives to place it correctly. Fortunately the mooring is only in about 15 feet at low tide.