Four miles out I sighted a long sickle fin cutting through a swell. Did I yell, "Marlin!"? I certainly did. An instant later Peter sighted another farther out, and this tail fin belonged to a large fish. I could not tell whether or not it indicated a black marlin. It stood up three feet or more, and that much would make a tail spread of over six feet. These marlin were riding the swells and they were moving fast. The tails would come up out of the top of a swell and cut the water at more than a ten-knot speed. Then they would vanish. It is always necessary to run the boat in the right direction to head the fish off. The Avalon is fast - she can do eighteen knots when opened up - but we could not catch up with the big fellow.