[captndale]

Depending on the state in which you are diving, there may be minimum size requirements for the flag to be legal. That said, flags flown from boats should be proportional to the size of the boat. Flags that are intended to be towed by a diver are better seen if they are large and flown higher above the water. However, the larger the flag and float the more windage, drag and resistance to waves they have. It can be very fatiguing to tow a large flag/float through the water, especially in adverse weather conditions.