how many boats on a start line?

Gate starts are simple in practice, it is only because they are not covered often in youth training that ppl think that they are complicated.

A typical method of gate starting is:

• A boat is nominated as the pathfinder.  (this boat usually finishes 5 / 6th in the previous race).
• The committee boat carries out a count down similar to that in a line start.
• At the start gun, the pathfinder has a minute to pass below the committee boat close hauled on port tack.
• The parthfinder is followed by a power boat, matching the pathfinders speed and course.
• The rest of the fleet starts by passsing behind the pathfinder and guard boat on starboard.
• After a few minutes, the guard boat releases the pathfinder (allowing it to tack off if desired) and continues in a straight line (or stops and drifts).
• The "gate" is between the committee boat and the guard boat and starting boats must pass between them within a few minutes.

The starting boats must decide when they want to cross the line:

• If they are faster than the pathfinder or the left of the course is favoured, they start just after the pathfinder has begun its run.
• If they are slower than the pathfinder or the right of the course is favoured, they start near to the end of the pathfinders run.

Technically, all boats cross the line at equal speed and time (assuming pathfinders speed is constant). 

Hope that helps clear a few things up.