Please excuse my ignorance. I've only been sailing for a few weeks.
I've been sailing a bit on J24s at my club. One of the skippers was telling me about steering by the jib telltales. My understanding is that, when sailing close hauled, you have to adjust your course so that the angle of attack is optimised.
OK I get that. But doesn't that mean that the classic points of sail diagram from the textbooks is a lie? You can't sail a reasonable speed in any direction from 45' to 315'. You sail any angle 90' to 270', adjusting the trim appropriately, but when in comes to sailing close hauled, there is only a single sweet spot angle at which you can sail efficiently - any further up and you luff, any further down and you stall.
So my questions are:
(1) Is this right?
(2) What determines the angle - is it fixed for a particular boat, or does it depend on crew weight and wind speed?
(2) The optimum angle depends of a lot of factors - read my long explanation below
To put this into a context.
When racing (or cruising) we often have to get the boat to a mark (position) directly upwind from where you start. In this case the we aim to get the boat moving towards the mark as fast as we can (the speed towards an upwind target is called VMG).
-If we sail as high into the wind as we possibly can we loose speed but shorten the distance
-If we sail to low we increase the speed and distance to go
-The sweet spot is somewhere in between
The optimal angle depends on lots of factors
-The boat (including crew weight, sails and other factors)
-The conditions (wind, waves)
Some instruments can calculated the VMG, we use this to find the optimal close hauled angle.
So the normal procedure when going upwind towards a windward mark is to adjust the sails for the optimum angle and steer the boat using the telltales.
If you have small changes in the wind direction while going upwind you adjust the course (using the telltales) or tack depending on the situation.
If we are going upwind but not aiming for a point directly upwind (not sailing close hauled) we adjust the sails to the course we want to sail. You can still use the telltales to steer.