Chris Tibbs is a meteorologist and weather router who has sailed over 300,000 miles here, he offers his advice on routing for multihulls

Over recent years there has been a big increase in the number of cruising catamarans making the transatlantic crossing. Of the 250 yachts crossing the Atlantic with the ARC and ARC+ this year, 60 (24%) were multihulls, and in some Caribbean anchorages monohulls are now the minority with private and charter catamarans dominating.

I’m fortunate in having raced and cruised multihulls on four transatlantics, along with half a dozen passage speed records on Playstation, the late Steve Fossett’s maxi cat. As a meteorologist and weather router I also help a number of catamarans which are cruising around the world.

Routing fundamentals

Weather routing is all about getting a boat from point A to point B in the optimum way. This is usually considered to be in the fastest possible time, but when considering a transatlantic or ocean passage I’ll often be asked for the most comfortable or safest route.

Looking at the ARC, the most direct route from the Canaries is a northerly route which – for around two out of every three years – will likely be faster than the traditional route of heading south towards the Cape Verde Islands, then west. This was not the case last year as a large wind hole covered the mid-Atlantic northerly route for the 2023 ARC. In a more usual year, some of the racing boats will take the northerly route while the more cruising oriented boats will head south.

The 2023 ARC fleet almost entirely followed the southerly route. With low pressure near the Azores drifting south-west, a southerly route across the Atlantic was the only real option

There are a number of reasons for this; averages suggest that a southerly route will give more consistent tradewinds and more comfortable sea states while the northerly route will often include a period of beating to pass through a trough mid-Atlantic – which is fine if you are racing, but it does tend to spoil the dinner if in cruising mode.

It also holds an advantage for the faster boats as the weather, for the first part at least, is likely to be close to the forecast but for a slower yacht two weeks into a passage the forecast may have changed significantly, and the northerly route may become less attractive.

For accurate routing – either by a skipper/navigator on board or using an onshore router – it’s very important to match the boat’s performance polars to the expected weather and sea state. Professional crews will spend inordinate amounts of time working on performance polars but for cruising yachts we usually make do with the design polars (or slightly modified ones) and when offshore we would drop them to assume the boat is sailing at about 80% of polars.

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How to weather forecast on passage

While it’s essential to monitor the conditions when choosing the best weather window for departure, equally important is being well-versed…

It is easy to buy expensive routing software and, with a little bit of work, a skipper/navigator can download the forecast, add the boat’s polars, press a button and get the optimum route. Some forecast providers (Predictwind being the best known) will offer cloud routing where, by entering your boat polars and route, routing is done ashore using different weather models and the results are sent to the boat. This saves a huge amount of downloading when offshore.

However, routing is a lot more than entering the latest GRIB files and pressing go. Ashore we have access to larger amounts of meteorological data, satellite images, as well as being able to modify advice to accommodate crew preferences. On long passages crew experience is important and we can choose routes on probability, making safer choices or high-risk high gain choices.

Multihulls routing

It is easy to group all multihulls together, however there is a great deal of variability between different designs and purpose. My first consideration when routing a multihull is: is it a performance or a cruising cat? Unless we are looking at an out and out racing machine I have a very crude definition – does it have daggerboards or not? Generally, more performance-oriented catamarans have additional foils. A second classification I use is – does the cat have a flybridge? The heavier the catamaran, the less its performance.

Parasailers are specialist downwind sails popular with cruising catamarans. Photo: Chris Tibbs

Performance cats

In general, performance cats are set up for sailing angles and we route in a similar way to racing boats. As they’re not restricted by waterline length rules to the same extent as monohulls, the fastest route will be gybing downwind and VMG sailing. Looking at the example of the ARC, the fastest catamarans are often the ones that sail the most miles.

But on rallies like the ARC and most ocean passages boats are fully loaded and heavy. There is a conundrum with catamarans as you have ample space for all the toys and a large tender RIB, but every added kilo makes it more difficult to sail quickly and increases the gybe angle.

Many people tend to sail cruising catamarans more downwind than their designers originally intended. Catamarans often have asymmetric reacher sails, usually set on the centreline, often on a bowsprit. However, for long downwind passages more specialist downwind sails may be carried, for example a parasailer (or equivalent) or twin headsails. This becomes more like sailing a monohull and speeds on downwind routes will usually be similar to a comparably sized monohull.

There are other considerations. If a crew is hit by a squall in a monohull with too much sail up this could push the yacht into a broach, but after a dramatic few minutes they’re likely to get going again, chastened but under control. Multihulls need a bit more of a careful hand and the more performance they are, the more care needs to be taken. On racing multihulls there is always someone standing by on the sheets, and any threatening squalls and potential gusts are monitored. It’s more critical if hit by strong winds to react correctly.

Lighter performance multihulls with Code sails will tend to sail angles and often cover additional miles on a typical transatlantic crossing. Photo: Outremer

Cruising cats are unlikely to flip as their weight and sail area are designed to prevent this, but even on a cruising cat bearing away and burying the bow can have unpleasant consequences. The only time I have ever deployed a drogue was bringing a cat back from the Caribbean somewhere north of the Azores. Big waves and a strong wind meant that we were surfing down waves, but then burying the bow in waves in front which stopped us dead and covered the boat in water – the drogue was deployed in record time!

Playing safe

So when routing multihulls we aim to avoid areas of high squall activity and strong winds, which is particularly important for the eastbound return trip from the Caribbean. Here I will generally advise a more southerly route. A large sea state may also be particularly uncomfortable as a cross swell can give an unpleasant motion.

One of the most useful parts of a weather forecast is knowing what will happen next; on multihulls it is good to sail by the numbers as you don’t feel when you are getting overpowered in the same way as on a monohull. Speed limits help to ascertain when you are pushing a little too hard and by reducing sail a lot of strain will be taken off the boat. When forecasting and routing, the stability of the atmosphere and the likelihood of gusts should be taken into account, and if they cannot be routed around then at least crews have warning.

Whether routing onboard or ashore, knowing the boat is critical as is knowing the crew’s capabilities. And while the principals are the same for catamarans and monohulls, being a little more conservative with cruising cats helps keep out of trouble.

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