Start with shorter legs than feel ambitious

The south coast is the best place in Britain to learn what a coastal cruise actually involves. There are plenty of harbours, few long stretches of unforgiving coastline, and tidal streams that are largely predictable once you get your head around them. What catches people out on a first cruise is not seamanship, it is optimism — planning a 45-mile day because it looks tidy on the chart, then spending the last four hours beating into a sea breeze with tired crew and a cold supper ahead.

Choose your first cruise as a series of legs you could complete in three to four hours, with a comfortable margin. Fifteen to twenty nautical miles per day is plenty in a catamaran. Build in a rest day. Decide in advance that a stay-put day is a success, not a failure.

Pick legs of three hours or less

On the south coast you can string together a genuinely satisfying cruise out of short hops. A few patterns that work well:

• Solent and western approaches — a night in the Hamble or Cowes, then Yarmouth, then a fair tide out through the Needles to Poole or Weymouth.
• Chichester and Langstone — sheltered, shallow, forgiving, and full of anchorages that suit a catamaran's draft.
• Weymouth to Dartmouth — a proper 45-mile leg, but excellent for a second or third season, with Lyme Bay's swell given the respect it deserves.
• Salcombe, Dartmouth, Fowey, Falmouth — each a strong day-sail from the last, with plenty of bail-out anchorages if the weather turns.

Write the plan down, but treat it as a menu rather than a schedule. The skill is in knowing which two or three options are available from wherever you are, not in sticking to the original idea.

Let the tide set your timetable

On a catamaran, tidal streams matter more than raw speed. Two knots of foul tide will take most of your progress and all of your patience. Roughly speaking, in the Channel the east-going stream runs through the hours before high water and the west-going stream after it, but that is a guide and nothing more — always take the day's figures from your own tide tables and check them against the almanac's tidal stream atlas.

Plan to be at the awkward places at slack water, or with a fair stream running:

• Hurst Narrows — punchy on the west-going stream at springs, and the Shingles Bank sits where you would rather it did not. Stay in the main channel.
• Portland Bill — give it two or three miles, or pass close inshore only with local knowledge and a settled forecast.
• Start Point and Prawle Point — uncomfortable in wind over tide and busier than you expect with pot buoys.
• Any harbour entrance with a sill or a bar — arrive on the flood and with rising water underneath you.

Allow for a metre of under-keel clearance as standard. Your shallow draft is a gift, but not a licence to cut every corner on a falling tide.

Identify your safe havens before you need them

Before you leave each morning, know three places you could run to if the wind, the engine, or a crew member's stomach goes wrong. Note the entrance, the depth at low water, the direction of shelter, and whether you can anchor or will need a berth. Useful bolt-holes along the south coast include Poole Harbour, Studland Bay in settled weather, the Beaulieu River, Bembridge, Chichester Harbour, the Dart, and the Yealm.

Carry a written list in the cockpit: harbour, distance, bearing, VHF channel, and notes on the approach. It takes ten minutes to compile and it removes an enormous amount of stress when a forecast shifts at four in the afternoon.

Wait for the right weather window

For a first cruise, treat a steady Force 3 to 5 as your window, and make sure the direction gives you a reach or a run. Wind against tide at the headlands is the single most common cause of a miserable day, so check the two together rather than the wind alone. A metre of swell against a spring ebb at a headland is a steep, ugly sea even in a decent catamaran.

Read the inshore waters forecast, then look at the four-day outlook and the actual observations from a station upwind of you. Sea breezes will fill in through the afternoon along most of the south coast in summer, adding ten knots in the early afternoon and dying by evening — which is a good argument for arriving early. If the forecast is marginal, go somewhere closer instead. There is no shame in it and your crew will thank you.

Catamaran housekeeping that makes the difference

A few things are particular to cruising a catamaran on this coast. Your windage is substantial, so marina berthing in a crosswind needs a plan before you enter: which side, which engine, which spring line first. Two engines make slow-speed manoeuvring easy, but they also tempt you into going faster than you should in a tight harbour.

When anchoring, set a bridle over the bow roller to stop the boat snaking about, and lay out at least five times your depth in chain. Your shallow draft means you can tuck into places monohulls cannot — with a metre and a bit under the keels you can lie closer inshore at Studland or in the Dart, but check the tide before you settle in for the night.

Under way, accept that a catamaran slams when driven hard to windward in a chop. Reef early, keep the speed down, and pick a downwind or reaching course where the motion is kind. Two hulls, two engines, and a shallow draft amount to a very forgiving boat — which is exactly what you want for that first, cautious, thoroughly enjoyable run along the south coast.