Learn English – The feeling of a storm approaching

There isn't a single way to reduce "sail power", hence no single term for this. There are several terms for specific actions that may or may not do the job, depending on the circumstances being reacted to. Reviewing some of the more likely and less likely ways to accomplish a reduction of sailing power, you can see that there's no word that is exactly what you're looking for:

• One may douse the sails, if the rigging is such that suddenly dropping the sails is possible.

• You can ease (not "ease up") anything under tension, including sails' rigging. The lines controlling the sails are the sheets and the most likely candidate for emergency easing. This can be done quickly, though loose, flapping sails can be dangerous, especially with larger sails, so easing an entire sail is not a default emergency measure.

• The boat can be put in irons (i.e., robbing it of all wind power and getting it "stuck") by turning it directly into the wind, but that's a fairly drastic effect on one's control of the boat for little gain. Conceivably, in an emergency that could be an intermediate action to gain some breathing space to deal with the sails directly.

• More abstractly, you can bleed wind from the sails, but that doesn't describe a specific action. Actually, this may be closest to what you're looking for, as it describes a specific kind of reaction to an emergency. It's not a general term, though, as it doesn't cover dousing or reefing, for example. It's an appropriate measure when just a little bit less wind will correct a problem or impending capsising, so possibly not the term to use when responding to a sudden storm.

For reference, reefing sails actually means to tighten them to their minimal area without entirely removing them as wind surfaces. Furling is to wrap a sail so it has no wind surface. Depending on the rigging, reefing may be a necessary part of the process of furling a sail.

The words that come to my mind are mesmerizing, emotive, poignant, melodic, inspirational, sublime, and ethereal. There's something almost angelic about the way the song sounds, at least the flute version.