Multihull Seamanship: An A-Z of skills for catamarans & trimarans / cruising & racing

By Gavin Le Sueur

This is an A-Z of seamanship skills for multihull sailors. There are many textbooks on the market which detail general seamanship principles. This is not one of them. Multihull Seamanship is about sea-going catamarans and trimarans and the skills needed to understand and enjoy them to their utmost. Both racing and cruising yachts are catered for, as are trailer-able multihulls. Seamanship is not a black and white skill. It is an evolution of knowledge; a building of information through experiment, thought and experience. There is no definitive word on an evolving skill. Multihull Seamanship started as Dr Gavin Le Sueur's personal index of 'how-to's. It has grown through experience and others sharing their knowledge. It should be on the book shelf of every catamaran and trimaran. This book is for people who are already multihull sailors, or for those who are contemplating multihull sailing. It has served this community for over 20 years and this second edition is fully updated. It is illustrated with delightful line drawings by Nigel Allison.

• Language: English
• Publisher: Fernhurst Books Limited
• Release date: Mar 20, 2018
• ISBN: 9781912177653

Gavin Le Sueur

Gavin Le Sueur built his first multihull, a 16 ft Mosquito catamaran, while at high school. After graduating from Melbourne University in Medicine, he purchased and moved aboard a 35 ft Hedley Nicol ‘Wanderer’ trimaran. To learn as much as possible about multihull sailing he decided to compete in the two-handed bicentennial Around Australia Yacht Race with his future wife. For this adventure they obtained the then fastest offshore racing catamaran in Australia – a 37 ft Crowther Super Shockwave named D Flawless which they raced in many Southern Ocean races. In one of these they sailed through the eye of a cyclone and completed the race only to be struck by a whale when sailing back home and forced to abandon ship. They were lent another catamaran for the gruelling around Australia race which they completed, getting engaged on the finish line. Since then they have owned 5 different catamarans in which they have cruised and raced in Australia and explored the Pacific and south east Asia.

Book preview

ANCHORING

Anchoring a multihull successfully requires choosing the correct location, having the right anchor for the boat size and bottom conditions, setting the correct chain and rode arrangements and burying the anchor effectively.

There is no anchor that covers all bottom conditions. Most multihulls should carry two anchors of different types. The classic brands come with recommended weights for yacht length but also consider how much windage your multihull makes. Do not underestimate the required anchor weight because your multilhull is lighter than a monohull of equivalent length.

Multihulls put a different load on anchors as they sail on the mooring line. Windage is important when selecting the anchor size. Some multihulls are aerodynamic and low windage. Others have a salon profile with flat surfaces that create high windage.

In most situations multihulls need about one size bigger than for an equivalent sized monohull. In the traditional anchors this means a heavier anchor.

The features of each anchor type are found in most general seamanship books. Anchors that will readily reset themselves are an advantage in varying current and wind directions. Racing multihulls in specific locations can utilise lightweight anchors. Cruisers anchoring in variable locations and conditions will need a heavier anchor.

Carrying a second anchor of a style that can be set via the dinghy is useful if you have to kedge off the bottom or set up a system to avoid wide swings.

For secure anchoring, your yacht should point into the wind and be as directionally stable as possible. Use the longest practical scope – usually a minimum of 5:1 rode length to height from forward beam to the bottom (at high tide). You want the chain to pull horizontally and not lift the anchor.

Multihull Seamanship Rule

Always anchor with a bridle. Run a lazy loop.

Illustration

The bridle arms should be approximately the beam of the multihull and no longer than the length of the yacht. Always have the ability to play out more scope or take line in. One way of achieving this is to have the bridle arms permanently arranged and spliced together in a single line. This single line is then tied to the anchor line with a rolling hitch finished off with a half hitch. You can also use one of the many chain grab hooks attached to the bridle bitter end.

If anchoring with all chain, then the chain section between the bridle attachment and the boat does not take any load – but it has an important role on multihulls. This ‘lazy loop’ of chain should hang well down into the water and will act as a catenary on the bridle attachment point. This will take wind and wave shock out of the anchor line as the weight of the lazy loop is lifted when the multihull pulls backwards.

Anchoring with a bridle is essential for wing masted and rotating rig multihulls. Lock the mast fore and aft where it is less likely to create drive. If the locking device fails the wing mast may create movement and oscillation. If this occurs the multihull might sail forward and break the anchor free.

Illustration

ANCHORING PROBLEMS

Multihulls move more to the wind than to the current and are thus more liable to change the direction that they lay over time. This pulls anchors out and can result in fouling of the chain in weed and rock.

Multihull Seamanship Rule

Know your neighbour’s swing area. Beware of the swing difference between monohulls and multihulls.

This is especially important in areas of high tidal flow. If possible avoid anchoring in strong currents. Monohulls anchored nearby will swing to the current while a multihull may not – often creating havoc.

Illustration

HOW MANY ANCHORS?

At least two anchors and possibly three should be aboard most cruising multihulls. Two full anchors for different bottom conditions and a third lightweight anchor for use as a ‘kedge’. Fully test each anchor so you know its capabilities before getting caught in a critical situation.

The lightweight anchor can be laid as a kedge to pull your multihull off an obstacle if you run aground. It is very difficult to carry a large anchor with chain through a surf line or in a small dinghy. Multihulls are beached easily but are a bit harder to get off if the tide drops. A kedge anchor is extremely useful to secure the swing range in a tight anchorage.

Multihull Seamanship Rule

Carry a strong lightweight kedge anchor.

Illustration

BRIDLE POINTS

Ensure the mooring cleats used for attaching the bridle arms and the central tether tie point are strong enough to take the full weight of the boat. The same rule applies to the strength of the nylon warp or anchor chain. If you anchor with rope, then the rode should be able to stretch. If using an all-chain system, then also utilise rope with stretch in the bridle arms and have a ‘lazy loop’ of chain to act as a catenary between the bridle attachment and the forebeam. The minimum length of anchor line should be five times the height from the forebeam to the bottom at high tide.

Multihulls tend to move more at anchor and you will need plenty of chafe protection on the bridle lines.

If tied to a permanent mooring, make the bridle lengths short enough to prevent the mooring from hitting the hulls.

The problem occurs in calm weather or reversing currents and winds. Make up a second bridle for this situation or mark the lengths on your usual bridle.

If you do not have a bridle system set up on your multihull, then a single line set off centre (from an outer hull) will reduce the amount you sail around when anchored.

Multihulls with prodders (bowsprit spinnaker poles) require careful bridle length measurements to set up a working system and avoid chafe. Sometimes the bridle arms need to be longer or shorter than recommended and this can cause issues with chafe and lines getting caught on underhull fittings. A strong, extendable boathook is often needed to run lines and retrieve them.

Set up a system that you can use easily. If it is difficult to set up the bridle each time you anchor, then rethink your technique.

ANCHORING UNDER SAIL

Manoeuvring cruising multihulls under sail is a skill worth practising. Picking up a mooring buoy or dropping an anchor requires knowledge about how far your multihull will continue forward when sails are dropped or feathered.

Multihulls are lighter and have a low momentum and will usually stop forward progress in one or two boat lengths depending on the wind conditions. Practise initially in no wind conditions to gauge maximum distances.

SAILING ONTO A MOORING

Approach the mooring buoy, or area that you intend to anchor, on a beam reach. Sail with enough speed to avoid leeway (drifting sideways). Centreboards should be down. Aim about a boat length under the buoy. At the last moment round the boat up into the wind while releasing the sheets.

Drop anchor or grab the mooring and secure it while the headsail is dropped or furled. Ensure sheets and travellers will run free or you will start sailing as soon as sideways drift occurs. Secure sails to reduce windage and then set your bridle.

Illustration

SAILING OFF A MOORING

Multihulls are readily sailed off their mooring. Raise the mainsail first but leave the traveller and sheets slackened off. Determine which tack you want to sail onto and reverse the helm so that when the boat drifts backwards it will turn in the desired direction. Hoist or unfurl the jib and sheet it on the wrong side for the desired tack.

Illustration

Sheeting the headsail on the opposite side to the desired tack will drive the multihull backwards and onto the tack required. When pointing in the desired direction, tack the jib and quickly sheet it in to sail away. Sail off the jib first and, once drive is established, sheet in the mainsail. If you sheet in the mainsail first the multihull may stall and go into irons or drift onto the other tack.

APPARENT WIND

Apparent wind is the wind you can feel on a moving yacht. It is the combined effect of the true wind and the wind generated by the movement of the platform you are on. Multihulls generate a stronger apparent wind than monohulls due to their high boatspeeds. This can be both an advantage and a disadvantage.

The unwary can think they are pointing high into the true wind and sailing at a high speed when in fact they are pointing off the wind. In this situation, a tack might be 120 degrees or more. What is happening is that the apparent wind is ‘bent’ forward toward the bows with the accelerating boatspeed as the multihull turns further away from the true wind direction. If you are trying to point as high into the wind as possible then this is a trap for the unwary.

To point high into the wind and generate the optimum speed toward a destination to windward you need to do some calculations and experimenting with your multihull. There will be a ‘best’ windward speed for your size and shape of multihull.

This will vary with wind strength and wave conditions and it is good seamanship to have a notebook on the navigation table with your calculations.

Multihull Seamanship Rule

Understand and use apparent wind.

A typical data entry might be:

Wind 15 knots, Seas slight. Full mainsail and working jib. Windward 9 knots. Tacking angle 90 degrees.

There are several ways to determine the above calculations. Computerised instruments will give a velocity made good (VMG) to windward. You can also calculate these figures if you know the boatspeed and tacking angles.

Illustrated is an example of the effect on boatspeed toward a windward point at different wind angles. The true wind is where the wind is coming from. The apparent wind is the ‘wind you can feel’. The figures illustrated show the actual boatspeed and the speed toward the windward point (VMG).

Illustration

Know how to determine and work the apparent wind effect.

SAIL SHAPE

On racing catamarans, the lighter and faster the boat the flatter sails need to be to allow for the higher apparent wind. In contrast, cruising multihulls need a suitable sail camber for their maximum speeds. A close sheeting angle is a way to manage the apparent wind angle increase. The sheeting angle is the angle of the gap between the headsail and the mainsail. If the headsail is sheeted out wide, then it is difficult to point high into the wind. In strong conditions, this may make it impossible to sail effectively to windward.

In heavy conditions the true wind angle and apparent wind angles are much closer, therefore, deeply reefed sails with some shape are faster and more efficient that flat feathering sails.

Storm jibs should have shape, not be flat blades. When your multihull needs to beat off a lee shore in a gale then good sail shape can be life-saving.

THE WEATHER AND APPARENT WIND

Cumulus clouds often mean there is vigorous mixing of the lower levels of the atmosphere and thus there is less difference in apparent wind angles between the waterline and the masthead. In these conditions, less twist in the sail will maximise the use of apparent wind.

Illustration

A storm sail set, efficient rig and parachute ready.

RACING USE OF APPARENT WIND

Keep the sail’s centre of fullness about one-third of the way back from the front, especially on the jib. The windward telltales should be just lifting. In most situations, a high-performance multihull will