Expert Multihull Techniques

By Nikki Henderson

There has been a huge surge in the sales of performance multihulls and with them a need to know how to handle them particularly when it comes to specific multihull techniques. The market for these boats is broadening; multihull cruisers are upgrading, monohull sailors are upsizing, and even virgin boat owners are tempted.

Over the last 12 months, while coaching for Outremer, I’ve met hundreds of these owners, everyone from young families to retired couples moving aboard a new catamaran and setting sail on a circumnavigation. Handling a performance catamaran is achievable even for a novice multihull sailor. But there is a big difference between just ‘getting by’ on such a boat versus sailing efficiently, safely and in style.

The transition for even experienced sailors can be quite a step up. For a seasoned monohull sailor, the differences are obvious: increased volume and speed, and a lack of heel. Even for an existing multihull sailor, the handling and performance is noticeably less forgiving and requires a shift in focus and technique.

This winter, I set sail on a transatlantic with the new owners of an Outremer 55. They have previously owned another less performance-orientated catamaran but invited me on board to coach them to fine tune the boat, assist with routing, and help them take best advantage of all the performance their new yacht offers. Here are a few of the topics we focussed on:

Most non-planing monohulls will do approximately the same speed on all points of sail. However, a performance multihull might sail at twice, three, even four times its upwind speed on a reach.

For example, the factory polars of an Outremer 55 give its average speed in 20 knots of wind with a true wind angle (TWA) of 50° at 8.5 knots, but in the same windspeed with a TWA of 110° it’s 19.1 knots. That’s more than twice as fast. How do you make the most of this speed advantage? And how do you best manage it?

In a monohull it often pays to slog it out for days sailing the best course to windward as this normally gives the best velocity made good (VMG). A dead downwind rhumbline route is the usual strategy for longer ocean passages, rather than sailing more miles and wider angles.However, on a performance multihull it is important to prioritise reaching when route planning.

In upwind conditions on a long crossing, consider whether bearing off by even as much as 20° will result in a better VMG, even if it feels counterintuitive. In light winds bearing off to 70° or 80° TWA can be the difference between a totally stalled boat and 5 knots of boat speed.

Faster speeds open up the possibility of keeping up with pressure systems as they move around the globe. For example, if crossing the North Atlantic eastwards, ideally you’d leave the US in clear weather with a depression forecast to leave the American coast a few days later.

You could use its predicted track to decide how much north or south to add to your easterly heading, to ensure that as it catches up with you, you are sufficiently south enough of it to pick up its strong westerlies. As they approach, you will accelerate, and if you can hold the speed you can use that downwind airflow to push you most of the way across the pond.

Controlling and handling the boat at these higher speeds requires a change in strategy. Increased speeds and acceleration mean that the apparent wind angle and apparent wind speed change much more frequently. So you need adaptable and flexible trimming and driving solutions.

Downwind the boat should be carving S-curves through the water to ensure it achieves the best VMG possible. If you can get this right you will attain the momentous double figure average speeds that a performance multihull offers, while also going the right direction! Instead of allowing the speed to plummet at the end of each surf, as the bow sinks into the bottom of the wave, a performance multihull can just keep on going.

1 Sail at higher angles to build up apparent wind speed (AWS) and boat speed.

2 Soak downwind as the apparent wind angle (AWA) surges forward with the acceleration.

3 Drive the boat back slowly upwind in time to maintain the average speed and continue the surf.

In an ideal world, to achieve this the boat would be hand-steered. But realistically, no cruisers want to be on deck for two weeks straight on a transatlantic crossing. Your best compromise is to invest in a top quality, well set up autopilot, as well as good wind instruments.

Set the autopilot to sail to apparent wind angle and watch how the boat slaloms through the ocean. The quality of the autopilot will really start to show its value when the sea state starts to increase. The best ones improve over time as they collect data and learn the wave patterns. If you aren’t sure exactly which AWA is ideal, choose a day that has very consistent wind and sail in open water. Set the autopilot AWA to 90° and then systematically increase the setting by increments of 5° at fixed time intervals until you get as low as you can before the foresail is shadowed behind the main. Measure the VMG by comparing the distance travelled at each of the different wind angles, and the average A to B course over ground (COG) achieved. This will give you a good starting point, and then it will shift further depending on sea states and wind strengths.

Another solution if you want fast speeds but don’t want to actively sail the boat to within an inch of its life is to use twist. Twist is a compromise between having a hardened sail that stalls when the wind goes aft, or a very eased sail that luffs when it goes forward. The more changeable the conditions, the more extreme the acceleration increases are, or the rougher the sea state is, the more twist you need.

The wide beam of a multihull allows for a long traveller, so most won’t have a vang. Sheet tension and traveller position are your primary controls to create twist in the mainsail. Begin by finding a full power setting in the main.

Set your autopilot to 35-40°AWA; most performance multis should make this upwind. Set your traveller at midships and over-ease your mainsheet so that the sail is luffing. Gradually tighten your mainsheet until the top telltale just flies. Manual winching offers better control here than electric.

Pull your traveller to windward until the boom runs down the centreline. The top telltale of the mainsail will now be flying about three-quarters of the time. If it is closer to 50% you may need to tighten the mainsheet further and then ease the traveller until you have achieved this (or vice versa). This is your full power sail shape, and your default car position upwind.

At this point some people like to mark the mainsheet (this doesn’t work with a continuous mainsheet). To begin with, just take note of the traveller position. If the conditions require more twist, ease the mainsheet, and pull the traveller to windward to keep the boom in the same position relative to the boat. You could keep a note of three traveller positions for each point of sail: full power, mid power, low power.

As the wind moves aft, you can add other ‘go-to’ traveller positions for different wind angles by easing the traveller down to leeward while keeping the mainsail shape set to ‘full-power’ mode. Once the wind goes aft of the beam, your traveller will be all the way down to leeward. Keep an eye on spreader chafe at this point.

Once you are happy with mainsail trim, you can trim the jib in a similar way, using car position and the sheet tension. Bring sheet tension in so that the leech shape looks very similar to the main: flat with a slight curve at the top. Then adjust the cars (if you can) so that the sail is not luffing, and the top telltales are also flying 50-75% of the time. Finally, walk forward to the forestay and view the slot between the sails. Do they look roughly parallel? If not, you may need to open up the slot a touch by moving the car outboard. This is your default jib car position for that point of sail.

When conditions increase, don’t forget to add twist to the jib too. Initially just ease a touch of sheet. Be careful moving the car too far inboard or you might close the slot. Moving the sheet attachment closer to the foot of the clew will open up the leech and create more twist.

Think of twist as the middle ground between sailing fully powered and reefing. Multihulls are much less communicative than monohulls. You do not have the obvious signs that the boat is overpowered, like a submersed toe rail or rounding up as the boat heels.

In time you’ll get to know your catamaran and build a connection to read how aggressively the boat is accelerating, its fore-aft pitching, sounds, and rhythm. But at first it’s useful to have some number guides and wind parameters of when to add twist and ultimately when to reef.

Generally a performance cat will require a reef much earlier because it’s lighter. I’d usually put in one reef at 20-25 knots, two at 25-30 and three reefs for 30-35 knots.

On our transatlantic crossing on the Outremer 55, contrary to my advice on the advantages of sailing angles downwind, we chose instead to sail dead downwind with the symmetric spinnaker up for the entire passage.

There are costs to taking full advantage of the speed of a performance catamaran. Averaging 15 knots boat speed is not everyone’s idea of comfortable. The hulls are so stiff that every wave that hits the hull sounds like the beating of a drum. The humming of carbon rigging, the swooshing of water screaming past the topsides, the slapping of the waves, the wind: it’s incredibly loud even when averaging 10 knots, let alone 15 or 20.

Performance multihulls are also so lightweight that they are really thrown about in a substantial sea state. Our decision to sail dead downwind rather than heating up and taking full advantage of the performance came down to the following reasons:

1. Lack of adequate autopilot We had one, but it wasn’t able to react quickly enough to the acceleration and resulting rapid change of wind angle that broad reaching would have created. It also struggled in a big seaway, so sailing with the waves square on to the stern was easier to cope with.

2. Sails We did not have a heavyweight asymmetric sail, which is what you need to sail these downwind angles (both our reaching sails were light weight).

3. Safety Akaroa II is hull No2 of a new design by Outremer. This was the first transatlantic crossing that this particular model of boat had ever done, so we were a testing ground and deliberately cautious.

Despite our conservative approach we still achieved 90% of the factory polars averaging 9.6 knots in sustained winds of 20 knots across the entire 2,700-mile route.

The trip took 11 days and 17 hours. The beauty of a performance multihull is that even if you don’t push it, you still manage brilliant speeds in the right conditions.

We calculated how much faster we would have gone, had we sailed the angles instead of running downwind. This assumes we would achieve the same 90% polars. TWA 140° appears to be the sweet spot.

Without any power being dispelled by heeling, performance multihulls will convert additional power into acceleration. With this increased speed comes increased loads on the lines, blocks, rudders, sail cloth and rigging. Winches are upsized. Jammers are used instead of clutches. Halyards are 2:1. You may be sailing on a 50-footer, but the loads are akin to a 70-80ft bluewater monohull.

A future owner recently reminded me of this, when he opened the main traveller jammer while holding the line with only one wrap on the winch. The lack of skin on his hand was gruesome evidence of how surprising the loads can be when a multihull is really powered up.

Interestingly, comparing a standard cruising multihull with a similar sized performance multihull, the opposite is true. A boat that weighs less needs less sail area to power it. For example, a Lagoon 450 has a sail area (main and jib) of 130m2 compared to an Outremer 45 (actually 48ft LOA) at 104m2. So, for the same apparent wind speed, there will be less load on the gear.

Watch out when sailing downwind. Due to a performance multihull’s ability to accelerate and hold high speeds downwind, it is easy to hold significantly more sail area in higher true wind speeds as the apparent stays low. However, if you do hit the bottom of a wave and stop dead in the water, the sail, rigging and lines will feel the full force of that wind.

Another reason to reef earlier than you think on a performance multi is that with swept back shrouds (needed to support the mast without a backstay) and a fully battened mainsail, even with the halyard eased downwind the sail may still not come down. You should be sailing with the minimum amount of sail cloth up to achieve the polars.

1. Rig up downhaul lines from each reefing point on the luff to help grind down the sail. Keep an eye on chafe on the leeward side on each of the batten pockets.

2. Use the rotating mast to open the sail to the wind more.

3. If that isn’t enough, come upwind to help get the sail down.

Switching to a performance catamaran may bring new trimming options: daggerboards, a rotating mast, and fully battened square topped mainsail.

Brush up on your fundamentals of sail trim so that you have a solid foundation to build on. When you first start sailing the boat, to avoid getting overwhelmed (which tends to result in people under-sailing their boat), begin by finding a base setting for all points of sail. Forget the rotating rig for now, but find enough twist in the sails that gives you enough height without too much power. Set the daggerboards as you would on a dinghy: down for upwind, up for downwind, mid-way for a reach. Then you fine tune.

When adjusting daggerboards, make sure you have your GPS track switched on. See if dropping a little more daggerboard helps with the COG upwind. Downwind, if you feel like you are on an ice-skating rink, try dropping a little board for better grip. If on autopilot, take note of the rudder angle. If it’s taking the helm from full starboard to full port then it might need some more grip, if not then a reef.

Be cautious of the risk of ‘tripping up’ in big seaways. In sea states much over 3-4m, it’s safest to lift the daggerboards and allow the boat to glide over the waves rather than risk one of the boards digging into a wave and destabilising the boat. While exceptionally unlikely to happen, if a daggerboard digs in, the worst case scenario would be a capsize. If you see any slick in the water that suggests the boat is sliding sideways over a wave, or an increase in heel, or significant water over the deck – these are signs that it’s time to lift the boards all the way up.

Finally, play with the rotating mast. At a basic level, try to get the mast in line with the foremost sail position and curve. The easiest way to see this is actually to stand forward of the mast and look down the line of the sail. It is in itself a foil and when in the right position can add the equivalent of as much as 10% more sail area. In the same way, you can use it to depower by reducing the angle.

When fine tuning sail trim I’d recommend marking all your tracks and angles of mast rotation, and once you are confident you could mark the sheets and halyards themselves. This is an exercise for the detail-orientated and it pays to be specific. Keep a notebook at the helm station to record your learnings, and over time build up not just ideal trim settings for wind and waves, but also polars.

Learning a performance catamaran’s sensitivity to weight can be a real learning curve. Compared to cruising catamarans, performance cats tend to be half the weight (or even less). Meanwhile, compared to a monohull the main difference is in the areas where the weight is most concentrated. A monohull’s weight is predominantly in its keel. Almost the entire weight of the boat is concentrated in around 15% of the boat’s length. Conversely, a multihull has no keel, so without that pendulum effect its centre of gravity is higher and less stable. On a multihull the weight is distributed along almost 90% of its length.

Step two is to arrange your belongings evenly around the boat. Ensure you don’t list the boat to port or starboard. Try to keep weight amidships and ideally low down. Avoid loading up the bow lazarettes or aft areas with too much weight.

When sailing, don’t forget that the worst kind place for weight is aloft. Without the keel, you significantly reduce the stability of the boat by having a furled Code 0 (for example) hanging around up the rig. It’s inconvenient to drop it every time, but it’s worth it.

Higher speeds, bigger loads, a lighter boat and higher centre of gravity don’t sound like the safest characteristics, and they aren’t if poorly managed. But you can also use them to your advantage. Being able to sail faster means you sometimes have an option to run away from bad weather.

But there are other safety drills that are worth thinking about ahead of time. What is your MOB recovery plan? With cats’ high freeboard, some owners plan to reverse up to the casualty and pick them up from the steps at the back. But how many have practiced that? Will it involve dropping the mainsail? Could the props injure the casualty? How does the back of the boat behave in a significant sea state? I’d recommend practising this until you have a plan that works for you on your boat with the equipment you have. The same should be said for plans to evacuate the boat, or deal with a fire on board.