Heavy weather means different things to different people. I suppose a more appropriate title for this entry might be sailing in rough seas.
The lucky boats are the ones that are not in the wrong spot when a giant wave climbs toward the heavens, then succumbs to gravity and descends like a horseman from hell into the yachts cockpit or rolls the boat over completely.
Roger Marshall in Rough Weather: Seamanship for Sail and Power. 2006.
I’ve made it my practice to avoid heavy weather…..storms….gale force winds….and the like. I have, however, intentionally sailed in rough seas so as to gain practical experience in preparation for unexpectedly getting caught in heavy weather. Of course, I’ve read books on the subject at hand in order to have a working knowledge and understanding that I could draw upon to plan a course of action if faced with unexpected heavy weather and rough seas.
First and foremost, before planning an ocean passage or even considering intentionally going out to gain experience in rough seas, one must have prepped a seaworthy vessel. It is not my intent to review the preparations and system of checks as well as safety equipment one must secure prior to assuming the risks of sailing in rough weather. Nor will I cover heaving to, use of drogues, sea anchors, tactics for finding a safe harbor, etc. What I wish to review here is a few tips on getting through the wind and waves. Hopefully, these considerations will assist you in making safe progress through rough seas until the wind and waves decrease or the storm passes.
Carry less sail than you think you might need. Reef! Prepare and use a storm jib if necessary. Use a preventer when sailing downwind in rolling seas. Take the sails in….sail under “bare poles” ……. if the wind is really strong. Don’t risk your rigging. Motor if required but be careful to steer the waves so as to keep the prop in the water.
When sailing or motoring upwind and into oncoming wind waves and swell the following depicted tactic seems to work well enough.

One of the most important things to avoid heading upwind in rough seas is in allowing the boat to crash down the back side of the wave. Bearing away going down the back side of a swell will prevent or minimize the jarring crash of the bow that is not only a discomfort for crew but probably not best for the vessel either.
If you must tack in heavy seas the best time to plan the tack is when the wind and seas have calmed a bit. If you must tack in rough seas then try to do so just before wave crest is at the bow of your vessel so that you are through the tack and headed down the back of the wave off the wind. Tacking in a trough between large waves is not suggested as the sails will have less wind, as it is blocked by the water, and you may not make it through the tack.
The following schematic depicts a reasonable approach to sailing or motoring downwind in a following sea.

One must be particularly careful to not go dead downwind so as to avoid an accidents jibe.
Avoid sailing downwind in heavy seas with a headsail alone as this can lead to mast failure if you do not use an adjustable backstay or running backstays.
When jibing take extreme care to slow down the process to avoid a broach. Jibe the mainsail prior to the headsail. Keep control of the headsail and it’s sheets to prevent it from being blown forward in heavy wind. I tend to try to make the turn through the wind in the bottom of a trough. One could also “chicken jibe” or tack to minimize the likelihood of failing at a jibe. If you choose this approach start heading up from the broad reach just after a wave crest passes, aim to tack through the wind in the trough and position the boat in a new broad reach as the next wave crest is arriving. Then, bear away as the wave crest arrives and passes.
At all times, be vigilant and avoid allowing the beam of the boat to become parallel to the waves as a breaking wave might knock down the vessel. Also, avoid pitchpoling and pooping. If you don’t know these terms then look them up!
I hope that these suggestions are somewhat useful. They are, I suppose, perhaps most useful to the coastal sailor who finds himself offshore experiencing unexpected seas that are the result of distant weather phenomena. At any rate, read, practice, and be prepared.
