Docking a catamaran

What changes when there are two hulls

A cruising catamaran is two hulls joined by a bridgedeck. The parts have the same names as on a monohull, but four things change the way she handles in a marina.

• Beam. A Lagoon 42 is 7.70 m wide on 12.80 m length. A Beneteau Oceanis 40.1, a monohull of almost the same length, is 4.18 m. That matters in narrow entrances and marina fairways, and when you choose a berth.
• Two engines and two rudders. Most cats have two engines and two rudders, and the propellers sit further outboard than a monohull's, one each side.
• Windage. She has high topsides and more windage than a monohull at low speed.
• No heel. She stays flat, so under sail she gives you none of the heeling warnings a monohull does.

Steering with the throttles

Because her propellers are so far apart, the cat's engines can turn her without moving her far. Put one ahead and the other astern and she pivots in her own length: port engine ahead with starboard astern turns her to starboard, and the reverse turns her to port. Used together, the two engines drive her ahead or astern.

That gives you three ways to place the boat in a marina: the wheel, both engines together, and the engines against each other. Practise each one in open water before you need it. In a tight fairway, slow right down, spin her where you want her, then drive in straight.

Coming alongside

The usual way to spring on to a pontoon, as taught for yachts, is to rig a midships spring about two-thirds of the boat's length, then:

1. Approach slowly at 30–45° to the pontoon, aiming at the middle of the gap.
2. About a boat's width off, turn to come parallel.
3. The crew steps off and makes the spring fast.
4. Let it take up, put the helm away from the berth and give her a little ahead. Adjust the helm until she lies parallel, with more revs if the wind is blowing her off.

A midships spring lets her pivot about her centre, so she is easier to keep parallel. The cleat must be at or just behind her pivot point. Once she is held on the spring, the spring, not the engines, controls where she stops.

Leaving the pontoon

To leave bows first, fender the quarter that will press on the pontoon, hold her against a spring with one engine and use the other astern.

The full lesson on springs and berthing, with a catamaran section, is Module 16: Anchoring & mooring. The parts of a catamaran are in Module 01, which is free.