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Spectacular squalls all around

Stunning sunrise. Spectacular and dramatic clouds and squalls developing as the sun peeks over the horizon. 

A day of squalls, a dramatic sight, a phenomenon not just as aesthetic as it can get out at sea, but also potentially dangerous and based on interesting physics and fluid dynamics. 

Basically, the air just above the water is heated by the high temperature of the ocean surface and starts to rise. It climbs up in the atmosphere expanding as it goes until this air mass reaches a level when it has cooled enough to start condensing its moisture. This condensation process itself releases more heat which makes for more of the rising. That retro-feeding process goes on until eventually a large cloud has built up. On its higher parts it reaches a point where the condensed droplets are too big and heavy and fall down. On its fall they pass through the ascending air, which is warm. Then the opposite process takes place. When evaporation happens it cools down the air on its way, this becomes denser and plunge. 

Droplets falling and plummeting cold air: rain and wind. Two of the main characteristics of a squall. 

The bursts of higher wind generated by them most often warn before striking. A cloud growing from the ocean surface in a localised area, a drop in the temperature, whitening water surface due to the breaking waves. A look at the Radar, showing the size and the rain clutter it has associated can approximately indicate how strong it is. 

The stronger winds usually precede the cloud sweeping by the ship, followed by downpour. Lighter winds normally follow afterwards when the showers and gusts have passed. 

And as it goes, between squalls and sunny weather we spend the nice sailing morning. Just before lunch a dark cloud associated with all those indications make for dumping the higher gear with the wind increasing to the upper 20’s knots. Royal and Upper Staysails are set again after lunch when it passed. 

It is not just the strength of the wind that is affected by those showers but also its direction. Most common are shifts of 15 to 20 degrees away from the general windfield, towards the south in the Southern Hemisphere. 

But today it was not only because of the showers that the winds change and shift, but also its general pattern. Last night we sailed on light 10 to 12kn Southerlies as we steered on a West-northwest course. During the day it becomes stronger and makes for bracing sharper and sailing Close-hauled for a while before becoming a steady South-easterly and even East-south-easterly. Braced a point to square again, we spend the rest of the day. It was not until the evening when it started to gradually ease. 

All in all, a great sailing day. Wind shifts, the spectacle of numerous squalls, and general good winds. A bit of sail handling bracing, dousing, and resetting sails that brought us 137nm closer to Easter Island, now 952nm from us. Today we passed the halfway to our destination. 

Geschreven door:
Jordi Plana Morales | Expedition Leader

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