The solution is to store them in a horizontal position where the motion of the boat shakes the chemicals back and forth in the cylinder and does not compact the chemicals. To check on whether your extinguisher is in working order, make sure the pressure gauge needle is in the green, and when shaking the cylinder you can hear the contents moving inside. You may also invert the extinguisher and hit it on the bottom with a rubber mallet. In some cases that will loosen the contents enough to insure the unit will work. If there is any doubt, dispose of the extinguisher in a proper manner and replace it with a new one(s).