Otherwise, it's not fair to the majority who did make it on time. Check with those on shore before committing. Get out on the water in time to 'nail the wind', determine and set up the course layout and, assuming conditions are suitable, be ready to commence a start sequence on time. Either the line is too short the wind too strong or the anchor not suitable. If, as PRO or RO, you are not familiar with an RC boat or driver, make absolutely certain that the anchor gear is adequate, by going out on the water and have the driver practice anchoring in deep water, in ample time to make necessary equipment changes before the event.
Competitors understand the start line is set when line flags are raised.
When moving the line, lower both flags as a clear signal that it is not set. This applies even when throwing out another 50' of line to square up a few seconds before the Preparatory Signal. Having endless general recalls because the wind is not true can be thoroughly counter-productive. At major events when there are many spectators, this can be a serious problem. If you cannot get compliance by hail or radio, enlist the help of a judges boat to move the offenders to a reasonable distance.