Parts of a mooring: how the pieces fit together

The system, from the bottom up

A mooring is a line of connected parts that runs from the anchor on the bottom to your boat. Exact setups vary with the harbor, the depth and the mooring service, but the parts are the same.

Anchor

The anchor holds the whole system to the bottom. In a soft-bottom harbor it is often a mushroom, which sinks into the mud and gains suction as the sediment settles around it. Others use a granite or concrete block, a pyramid or a helix. (How the four common types compare.)

Chain

Chain connects the anchor to the surface. It adds weight and keeps the pull on the anchor low and close to horizontal, and it takes the wear from the bottom. Many moorings use heavier chain near the anchor and lighter chain above it. The length of chain compared with the depth of the water is the scope. A longer scope lets the anchor hold better, but gives the boat more room to swing.

Shackles and swivel

Shackles join the parts, and a swivel lets the chain turn without twisting. They are small, they carry the full load, and they are some of the first things a mooring service checks. A swivel reduces twist in the chain, but it doesn't stop chain wrap. (Why a swivel doesn't stop chain wrap.)

Mooring ball

The ball is the float at the surface. It marks the mooring and keeps the top of the chain where you can reach it. It doesn't hold the boat. The chain and anchor do.

Pennant

The pennant is the line from the ball to your boat. It is the part that belongs to you, and the part you can see and check yourself. It takes the chafe, so it is worth looking at often.

Where problems tend to start

• The pennant chafes where it rubs the boat.
• Chain, shackles and swivel wear and corrode out of sight, and are checked when the mooring is hauled or dived on. (A checklist for boat owners.)
• The anchor can pick up chain wrap. On a traditional mushroom the stem is a vertical post, and as the boat swings the chain can wrap around it. It shortens the effective scope and raises the peak loads on every other part of the system. (More on chain wrap here.)

Where MoorSafe fits

MoorSafe replaces only the anchor. It is a mushroom with a three-bar cone above the stem, so the chain has nothing to catch on. The chain, shackles, swivel, pennant and ball stay the same, and it is set the same way, with a mooring barge or service boat. A mooring service can swap the anchor without changing the rest of the system.

This is a general guide. Your mooring service and harbormaster decide what is right for your harbor.