Big beam seas can be the most challenging, unpleasant and dangerous of all conditions to sail in. Exposing the entire length of your vessel broadside to oncoming waves allows the energy in those waves to have maximum impact on your hull.

This causes excessive heeling moment, which can result in broaching or, in extreme scenarios, a risk of inversion. Extreme conditions should, if possible, be avoided but here are my tips for how to handle the top end of manageable beam seas.

Passage planning

Use wave buoy data and wave height forecasts to assess sea conditions. Pay careful attention at the passage of fronts; a rapid change in wind direction will often cause big seas to break.

Depending on hull characteristics, wave heights of as little as 30 per cent of your length overall can start to become dangerous beam-on, so consider alternative routes early. Most routing software has an option to avoid waves over a certain height but make sure your GRIB files include wave data.

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Sail setting

Sailing fast through beam seas will allow your helmsman to steer around waves, reducing their impact on your hull; so don’t shorten sail too early. That said, your sails should be set to limit heel, as the force of oncoming waves will already be heeling the boat over.

When sailing in larger waves your apparent wind speed and wind angle can change so sail shapes should also be forgiving to allow for this. Go to town on twist: the bigger the waves, the more the twist. Slide the jib cars back to open the top of the headsail if you normally reach using an outboard lead, and consider moving the sheet to the inboard upwind track as waves get bigger.

Soften your mainsail leech by moving your traveller up the track, easing the mainsheet and vang and pulling on your backstay. Shorten sail when the combined heeling moment from waves and wind feels too much. You may need to harden up the leeches immediately after reefing, putting power back into the top of your sails to keep sufficient speed and manoeuvrability. As conditions continue to build apply twist again.

Helming

Helming in big beam seas takes skill and concentration. Good helming in these circumstances is about anticipation and feel. Employ all of your senses to dial into wave patterns; you will start to sense the size of oncoming waves by how the boat feels underneath you. Look for relatively flat spots between them and steer dynamically from one to the next.

If you are not able to avoid a high crest or breaker, take action to minimise its impact on your hull by heading up or down. Don’t underestimate how challenging helming can be, so don’t rely on one person and if there is the option to alter course, then take it.

Autopilot settings

Older generation autopilots can really struggle with beam sea conditions and usually require tuning. Here are a number of pointers to help:

• Remember sail trim: if your pilot is constantly rounding up when you heel first try more twist, then reef. In big conditions set the pilot to steer a true wind angle. If your system does not have this function consider changing course to head into the waves.
• If you can, maintaining speed through beam seas will help the helmsman to steer around the waves, but don’t shorten sail too early this function consider changing course to head into the waves.
• Bear in mind that your pilot cannot see oncoming waves and does not care about your welfare; try actively steering through wave sets using the control pad. This is less tiring for the helmsperson and more comfortable for the crew (remote controllers are great for this).
• Increase response or gain so the number and size of corrections the pilot makes per minute matches those of your helmsman. Also increase counter rudder settings if your pilot is weaving an ‘S’ shape after corrections. And increase wind damping or decrease wind response to allow for the amount of extra movement at the masthead caused by wave action.
• Charge your batteries, as this will be a power-hungry point of sail for the pilot. Some modern pilots are now able to measure pitch and yaw and automatically adjust settings to match whatever the conditions.

Precautions

Avoid big beam seas if at all possible, but if you do get caught out in these conditions make sure washboards are in and tied in place. Crew should be harnessed on short tethers, keep a good look out using AIS and radar and ensure everything below is well stowed with locker doors, top opening fridges and floorboards secured in place.

First published in the February 2018 edition of Yachting World.