Rachael Sprot talks how to deal with squalls and gusts and also looks at exactly what we mean by the terms gust or squallSqualls are the school bullies of the ocean. But, like all bullies, your best bet is to outsmart them \u2013 and that means knowing where they form, how to avoid them and what to do when they turn up uninvited.
\nSailing west across the Pacific to Tahiti we\u2019d had persistent squalls for several days, but they had all been fairly benign. We\u2019d diligently dropped, repacked and re-hoisted the spinnaker three times in one afternoon for squalls that turned out to be a complete non-event, so I finally gave in to the temptation to just leave it up.
\nAt the last minute a wall of white horses appeared under the cloud and we scrambled to drop the medium-weight symmetric. We bent a stanchion in the rush, but otherwise the drop went smoothly, although I was kicking myself for leaving the spinnaker set.
\nWhat are squalls?
\nThe World Meteorological Organisation defines squalls as \u2018a sudden increase of wind speed of at least 8m\/s, the speed rising to 11m\/s or more, and lasting for at least one minute\u2019. In other words, a 16-knot increase.
\nSqualls are caused by updraughts of air into the atmosphere. They are smaller and more localised than cold or warm fronts, but bigger than isolated showers and gusts, for instance as seen on and around land.
\nSqualls are made up of a complex combination of updraughts and downdraughts. Broadly speaking they suck in the air from in front and behind and spit it back out in the middle. The leading edge of the squall is usually the most violent in terms of wind, with a feature known as a \u2018gust front\u2019 and the likelihood of big changes in wind direction.
\nAs it passes overhead the squall brings intense rain from a cumulonimbus tower. This will gradually be replaced by drizzle from stratus clouds on the trailing edge of the system. Once the gusts have gone through there is often a period of complete calm before the prevailing wind fills back in again.
\nSqualls on the horizon: the crew of Turn the Tide on Plastic prepare to reduce sail during the 2017\/18 Volvo Ocean Race
\nSqualls are often arranged in lines because they\u2019re self-generating systems: new cells develop in front of the mature cells and the old cells at the back of the line die off. If you find yourself at the start of a squall line, watch out because the larger cells may be yet to come.
\nSquall distribution
\nSqualls are often associated with tropical tradewind sailing because they rely on a ready supply of warm, moist air in order to develop. In the tropics they travel westwards with the easterly tradewinds.
\nThere is evidence that ocean squalls in the North Atlantic are more prevalent on the eastern side of the ocean but anecdotally most sailors taking a tradewind route from the Canaries to the Caribbean will report more squalls in the second half of their voyage when they get closer to the Caribbean.
\nArticle continues below\u2026<\/p>\n
\t\t\t\t\t\t\tSurviving the Doldrums<\/p>\n
\t\t\t\t\t\t\tConrad Humphreys sees light at the end of a dark and turbulent tunnel<\/p>\n
\t\t\t\t\t\t\tBluewater Sailing Techniques Part 3: Coping with squalls<\/p>\n
\t\t\t\t\t\t\tDiscover the best way to cope with squalls and weather them safely in the latest instalment of our Bluewater Sailing\u2026<\/p>\n
This may be due to the fact that yachts on that route usually set off north of the squall belt but converge with it as they drop south throughout the passage.
\nTransatlantic sailors should guard against a false sense of security as conditions start off relatively stable, but a week or so into the passage the squalls arrive.
\nGlobally they\u2019re most prevalent in the Inter Tropical Convergence Zone, or ITCZ. If you\u2019re crossing it the best advice is to identify its narrowest point and have plenty of fuel available because between the ferocious squalls there are long periods of calm.
\nSince they\u2019re convective, squalls are easy to identify from a distance by their tall, towering clouds, which sometimes contain lightning activity. The heavy rain underneath is clearly visible from a distance and on radar.
\nAs a general rule of thumb the taller the cloud the stronger the rain and wind but there are plenty of exceptions to this. The likelihood of being caught by a squall can be assessed by its bearing: either visually or on radar.
\nUsually eyeballing them against a stanchion does the job and you\u2019ll soon know whether it\u2019s passing ahead, astern or converging with you.
\nSqualls on the horizon
\nAt night radar is a useful alternative: set up a Variable Range Marker (VRM) and Electronic Bearing Line (EBL) to monitor their position. If they\u2019re isolated you can often change course to avoid them by hardening up or bearing away 10\u00b0 early on. It may sound inefficient to zigzag around squalls, but if you\u2019ve got a complex downwind rig with gybe preventers and poled-out headsails set up, it\u2019s a lot less effort than taking everything down for ten minutes of fury, then putting it all back up again.
\nKnockdowns
\nAside from shredding your spinnaker, one of the biggest hazards of squalls is a knockdown. Angle of heel is a key metric in determining how vulnerable you are to a squall: if you\u2019re already heeled over at 20\u00b0 then a big squall is more likely to knock you over to a severe angle.
\nThis is because the pressure on the sails increases disproportionately to apparent wind speed. The pressure exerted in 16 knots of wind is 4.2kg\/m\u00b2, in 22 knots it is 8kg\/m\u00b2. Hence a 40% increase in wind strength will double the pressure in your sails.
\nThis doubling of wind pressure is the definition of a gust. Gusts are something we can reasonably expect to see in normal sailing conditions, but a squall is defined as a 16-knot increase in wind speed.
\nIf you\u2019re reaching in 10-15 knots of apparent wind and a 32 knot apparent wind squall arrives this is much more than a big gust. In this scenario the pressure on the sails increases by 400%, which is pretty intimidating.<\/p>\n
Another reason squalls are so difficult to negotiate is that the wind doesn\u2019t just increase, it also shifts unexpectedly so what was a comfortable broad reach can suddenly become a dead run or a close reach. The dead run puts you at risk of a crash gybe, and the close reach immediately increases your apparent wind speed.
\nCoping tactics
\nGiven that we can\u2019t control the mean wind speed, our only option when a squall approaches is to behave as though we already have 20-25 knots of apparent wind: in other words put in a reef or two, furl some headsail and make sure the helm is alert to wind shifts.
\nMost people choose to run before a squall keeping the apparent wind speed down and holding a comfortable broad reach, wherever that may take you. But there is a school of thought that heaving to or hardening up will allow the squall to pass through faster.
\nIt\u2019s a decision for each skipper to make depending on the circumstances. In areas of persistent squalls with intermittent lulls it is much easier on the crew and vessel to reef down and put the engine on: sail through the squalls and motor through the light airs.<\/p>\n
If you enjoyed this\u2026.<\/p>\n
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The post Squalls and gusts: How to predict and cope with them appeared first on Yachting World.<\/p>\n","protected":false},"excerpt":{"rendered":"
Rachael Sprot talks how to deal with squalls and gusts and also looks at exactly what we mean by the terms gust or squallSqualls are the school bullies of the ocean. But, like all bullies, your best bet is to … <\/p>\n