In a close hauled point of sail the sailboat is trying to sail into the wind.
It is a contest between the boat and the wind and the boat tries to beat the wind.
This point of sail is also called beating.
If the sailboat heels too much from a strong gust of wind, the boat can go slightly into the no-go zone, reducing heel and changing the course a little closer to the desired destination.
This is called feathering.
As the wind dies the boat bears away ( turns away from the wind ) and resumes sailing in a close hauled point of sail.
Sailing efficiently close hauled is also called sailing in the groove.
Trimming the Sails on a Close Reach
When sailing on a reach, the experienced sailor, trims the sails based upon the apparent-wind. This is important because sails cannot be efficiently positioned based upon the point-of-sail or the direction of the true-wind. An extreme example is ice-sailing on a broad reach, a sudden strong gust of wind can cause the craft to reach high speeds and cause apparent-wind conditions similar to a close reach.
On a close reach, one method of testing mainsail and jib position is to let the sail out until it luffs (the leech starts flapping) then pull it in (or trim the sail) until the sail is steady. It is easier to tell if the mainsail and jib are let out too much, than if the sail is over trimmed (pulled in). Telltales may also be used as a guide. Telltales are small pieces of yarn attached to the sail. Although telltales are helpful when sailing on a reach, they are not useful when running (sailing directly downwind). In a run, the wind should be perpendicular to the sail.
Whenever the sails are trimmed using the sheets a change in sail shape occurs. Other lines and the "fair lead" may have to be adjusted to maintain sail shape.
Sailor's Tip: If the outside telltale flutters, let the sail out. If the inside telltale flutters, sheet the sail in.
When you are sailing in steadier winds it's more important to maintain maximum
boat speed, and individual spurts have less significance. In this case you must
search for an upwind groove. When you have found it the boat will nearly sail itself.
It should have a very slight weather helm, and be sailing nearly flat.
Small changes in wind velocity and heeling moment will hardly change this feel
at all. But remember this steering groove is only made possible by the shape and
position of the sails. You must continually try to flatten your sails more to the
high speed, high pointing sail shape.
And if you start to sail too fat off the wind, the boat will gyrate quickly
from the weather helm to a lee helm as the boat becomes level again from its
former heeling angle.
But if you try to sail to windward this way you will be sailing more by
observing the leading edge of the sails than by really feeling the groove.
Sailors talk about sailing the groove.
When you are Close Hauling sailing and get too high (i.e. boat to direct into the wind) the boat will stall - sailing too low (i.e. too directly downwind), the boat will catch too much wind and heel excessively.
In high winds the groove becomes smaller – constant vigilance is needed in order to prevent the boat from stalling.
Stalling means loss of control - you don't want to be lying broad side to big waves.
If you do stall, be prepared for excessive heeling forces as the wind initially catches the sails - be at the ready to let the sheets out.
If you fall out the groove by bearing away too much, (turning the boat too far down wind), the sails will catch more wind and the boat will heel excessively. This requires letting out the sheets quickly, to regain control and then heading up to find the groove again.