135% vs 150%
Sails work within a range of wind strengths. A 150 is a light air sail, but there has to be enough wind to lift the weight of the sailcloth and hold it in the shape that drives the boat. If it''s hanging limp, and if you have enough crew to move them forward and to one side and heel the boat about 8-10 deg., gravity will help the sails hang in that shape. By moving crew forward, you will also reduce the boat''s wetted surface, reducing drag.
More often than not, you won''t have enough crew members to heel a ballasted boat to that extent in light air, so your other alternative is to raise a sail made of lighter weight sailcloth and lighter weight sheets. It takes less wind power to lift and hold the shape of a sail made of lighter weight sailcloth.
Also, in extremely light air, the wind isn''t strong enough to lift your tell tales, and that makes it difficult to know when the wind has shifted in its direction. Occasionally I''ve been on a beam reach and had the wind die, and sat there with limp sails waiting for the wind to come back, only to realize that there is air movement, but it is now coming from dead astern, but it is so light that it couldn''t lift the sailcloth or the tell tales. When the wind is that light, pay extra attention to the feel of the air on your skin. Sometimes (not always) you can feel it. You have to look everywhere for clues. The surface of the water can provide visible clues to the wind direction. It helps to light a cigarette or cigar, or anything that produces a smoke trail, because the smoke will react to even the slightest amount of air movement. Once you know the direction of the air movement, you have to either re-trim the sails for that direction, or alter your course to the course that will get you moving again and achieve the best velocity toward your objective, and then trim your sails accordingly.