by GreenLake » Tue Dec 22, 2020 8:14 pm
If you have too much wind power, you depower your sails by changing the angle of attack. (Or by reefing, if it's ongoing).
To change the angle you can leave the trim where it's at and turn into the wind which flattens the angle of attack (angle between leading part of the sail and wind). Or you can let out the main, which also reduces that angle.
If you fall off in response to a gust, leaving the sail trim as it is, you increase the angle of attack, and if you fall off far enough, you get your sail square to the wind, turning it into a drag device. At that point, capsize is inevitable (if your sails are still sheeted in). If you let out the sail while turning down, you end up with competing actions. However, the vector of your sail force moves forward, which, in theory, should reduce the heeling force.
You also end up not adding boat speed to wind speed as directly and once you are pointing downwind, you even subtract the former from the latter.
I'm not sure how suitable this is as a gust response, but it's clear that you can sail downwind in pretty strong winds and the winds will feel less. Let's say, you go from 5 knots upwind boat speed to 5 knots downwind. If your apparent wind was 25 going upwind, it will now be a balmy 15 knots. And sail force goes with the square of the wind speed, so that difference will be like 625 compared to 225, or, in other words, down to a third.
In dealing with a temporary increase in wind speed, gust, when sailing upwind, the goal is to keep the boat manageable while not giving up any gains made to windward. Hence feathering (luffing up a bit) or (better) letting out the main (ease).
If sailing downwind, the old saying is "down in the gusts". Going deep downwind is slow (because of the subtraction of boat speed), so you do that during a gust, while in the lulls, you come up again, which changes the angle between boat speed and wind speed, leading to an apparent wind that's a bit higher, and perhaps even a course where you can use the sails as foils instead of drag devices. With luck, averaging these two directions points at where you are going, so you get the best of both. If not, you'll have to gybe at some point, but still will be sailing faster downwind than pointing straight at your objective.
From your mention (I have not tried to find the video) it's not clear in which context these reported remarks fit.
~ green ~ lake ~ ~