Boats Adrift – Mooring Lines

Sadly, another boat came ashore on Saturday in the strong winds. The third this year due to its mooring lines parting. Luckily it came ashore when there were quite a few members at the club and they were able to hold it off the beach and prevent it getting damaged. With the strength of the wind, towing it with a dinghy wasn’t really an option. As it came off a mooring close to the jetty it was possible to get a long line from the mooring to the boat and pull the boat out and make it safe.

This highlighted another example of undersized mooring lines being used. Whilst modern ropes have extremely high breaking strains, for example English Braids, 10mm Braid on Braid is quoted as having a breaking strain of 3150Kg, enough to lift many of the smaller boats, it is unsuitable to moor even a small boat.

Even though the load on the mooring is never going to exceed the breaking strain, the problem is wear. Any rubbing movement of the rope against a metal surface will quickly wear through. We have seen such ropes fed from the boat through the shackle on the buoy and back to the boat. Using this method, it rapidly cuts through the rope at the shackle.

The following is some guidance to assist in selecting the correct rope for mooring.

Many members will have their own methods, but this is aimed at anyone not too sure how to attach their boat to the mooring.

When selecting rope for mooring lines it is best to go for the largest size you can get through your fairleads or bow roller. It can help if you can get a plastic hose over the rope where it passes through a bow roller.

Traditionally 3 strand Polyester or Nylon ropes have been found to be the normal choice as they can easily be spliced. Nylon has a bit more stretch acting as a shock absorber. However, when I last replaced mine the chandler recommended trying Polypropylene as it was popular on the river with the advantage of floating making it easy to pick up. I am currently using one Polypropylene and one Nylon line.

At the buoy end of the line an eye splice with metal thimble to protect from wear, can be shackled with an additional shackle to the shackle on top of the buoy. This way the line can be removed from the buoy to be stored ashore through the winter, keeping it clean. It is advisable to have two lines attached to the buoy. However, two lines with metal thimbles can suffer with wear from the thimbles rubbing the rope next to it.

Another alternative is to have soft eye splices in the buoy end of the lines. Using the eye splice pass the eye through the shackle and the other end of the line through the splice to form a slip knot which will tighten up under load and shouldn’t wear excessively.

If you can’t splice or need to attach a line quickly as on Saturday, one way to attach a rope that isn’t going to wear straight through is use a round turn and 2 half hitches around the shackle. A belt and braces approach is to leave the tail long and finish it off as a bowline. If the round turn and 2 half hitches was to slip or work lose the bowline would prevent it coming undone.

At the boat end the line either needs to be long enough make off on a cleat or have a soft splice to fit snugly over the cleat or bollard.