Technical maintenance

Heavy weather: the right course of action for multihulls

Talking about heavy weather implies that we’ve already defined the threshold beyond which we have to deal with it!

March 3, 2023

Talking about heavy weather implies that we’ve already defined the threshold beyond which we have to deal with it! Once the question has been asked, its treatment requires humility, but also experience to come up with some effective advice for those who have either missed the forecast, or undertaken a long passage with the hazards which that involves.

What is heavy weather?

Generally, with multihulls, it’s said that the problem is never the wind but the sea state. And that’s true, because it’s easier to deal with the former than the latter: you can reduce the canvas but you have to manage the waves. However, the fact remains that strong winds in multihulls can be a problem, especially when they appear without warning. This could be the case in some thunderstorms, or when, after sailing in the lee of an island, you are hammered at the tip of the land with 35 knots on the beam…

And although the sea is always the most dangerous, it is important to keep in mind that the force exerted by the wind on the rigging and sails is proportional to the square of its speed. This means that there is a much greater difference between 25 and 30 knots than between 30 and 35 and so on.

But the sea state remains the most significant: it is easier to sail in 40 knots of mistral along the Mediterranean coast than to set from the Brittany coasts into 30 knots of wind with a confused sea kicked up by successive passages of weather systems.

So, it’s not easy to define this heavy weather. Since the absolute values of wind and waves are of little help, let’s risk another approach: bad weather happens when uncomfortable sailing develops into a dangerous situation. In other words, it depends on the atmospheric parameters but also on the size of the boat, its preparation and especially the competence of the crew.


Credit picture: Jean-Pierre Fréry


Some rules for before the (real) bad weather:  

  • Reefing: First the mainsail:

Beyond the sail area difference, lowering the sail’s center of effort is very beneficial for pitching. If the seas are rough and even more so upwind, we’ll roll a little genoa in afterwards, or we’ll sail under staysail.  When sailing downwind, you shouldn’t hesitate to put a deep reef in the main, or even drop it completely with a rough sea. The helmsman can then manage to maintain his course more easily with much less tendency to luff up.

  • Upwind, we head up; downwind, we bear away:

When the boat accelerates too fast upwind or is struggling against the sea, head up a few degrees to reduce the speed and therefore the apparent wind. It is the opposite on a broad reach. Bearing away (without gybing) is the right reaction when the boat accelerates too fast down a wave.

  • And with the wind on the beam?

The problem remains the same: luffing up or bearing away carries the chance of accelerating in either case, increasing the apparent wind and therefore the risk. This is why you must keep one hand on the mainsheet at all times, ready to release it. With experience of your boat, you’ll know, according to the angles and wind strength, the right sail combinations, which will allow you to anticipate the need for reefing. The use of good navigation instruments in good condition and which are properly calibrated to obtain the right information on the strength and angle of the true wind is essential from this perspective.

Credit picture: Jean-Pierre Fréry


Strategies in heavy weather

  • Upwind, motor-sail:

A good tactic is to sail very close to the wind (between 35 and 45° to the true wind), under very reduced sail (the mainsail alone reduced to the deepest reef) and using the leeward engine. This allows the speed to be set according to the waves and possibly played on the throttle to better pass the crests or slow down behind them if necessary.

  • Running before the wind:

More comfortable, though not without risk, especially if the waves are short and steep. Even on long and organized seas, the problem remains to adapt your speed to the frequency of the waves. Try as much as possible not to have to run under bare poles, so as to maintain a certain amount of maneuverability. Be careful, however, to trim the small area of sailcloth remaining so the bows aren’t plunging, which would reduce the efficiency of the rudders. It’s all a matter of balance, even if that means trailing lines astern to slow down. The speed can be regulated by lengthening or shortening the drogue, which is easy to set up from the sugarscoops on a catamaran. The boat will remain in line, held by the stern.

  • Heaving-to:

With little sea room to run, and if it is difficult to climb upwind in rough weather even when relying on the engine, it can be tempting to heave-to. But it may prove very difficult to actually do. Of course in theory, a multihull can sit easily, flattening the sea in the wind. In reality, it is very difficult to stabilize, particularly because of the large windage of the hulls and superstructure.

Credit picture: Jean-Pierre Fréry

Credit foreground picture: Nicolas Claris