Originally Posted by DRFerron
The problem with that (pre everyone with a GPS) was that the CG and Navy plot in true (still do). If you give them a bearing in magnetic, they will not have your exact location if they had to come looking for you. They have no way of knowing, also, how much deviation is throwing off your compass.
Without a GPS (when, perhaps, your boat gets hit by lightning?), it would be in your best interest to learn how to do the calculation and to take a manual fix so that you can give them and you a better chance.
Yes, that is exactly what I was taught. The teacher was Navy and he said any communication with Navy or Coast Guard should be in true, but for his own navigation he used magnetic because it was his opinion that it was simpler and had fewer opportunities for error.