Chartering a boat and captain for a day of Chesapeake Bay fishing is like mail-ordering a mate. You don't know what you have until you have it, and by then it may be to late. A boat is a small place to be working out irreconcilable differences.

Although most skippers are decent enough, there is the occasional unpalatable captain who is either bossy or uncommunicative or grouchy or all three. You're paying good money to be miserable. What could be worse?"

One day last week I fished with Capt. Robbie Robinson, who charters out of Solomons Island. Conditions were poor and we didn't get the skunk out of the boat until after lunch, when a few blues and sea trout struck. s

But then I'd already decided that even if we caught nothing I'd count the day a success because Robinson was a good skipper. He was knowledgeable and willing to share his knowledge, hard-working in pursuit of fish, whether the slimy beasts cooperated or not, and he had a good, clean, well-equipped boat.

It reminded me how important a good captain can be and how easily a bad one can ruin a day.

One big problem when a city clicker hires a captain and goes fishing is the cultural gap that exists between a man who wrests his living from an unpredicatable sea and one who, say, compiles reports on the socioeconomic impact of group health organizations on Spanish-speaking communities in the Southwest.

In the interest of bringing charterees and charterers closer together and avoiding expensive disasters at sea, here is a little guide to some of the fishing captain type you may encounter.

THE LEGEND IN HIS OWN MIND -- If the fish aren't biting he will regale you with tales of great days he's had. He'll pull out yellow newspaper clippings describing a fantastic catch aboard his boat in 1956. He'll tell you about the '60s, when he caught 382 rockfish one day and nearly sank the boat. He'll tell you about radio shows that beg him to appear and tackle manufacturers that plead with him to test their equipment. You'll want to test your equipment on him. Your hunting equipment.

THE CLAIM -- He won't say a word. Fish will be leaping into the boat. You will say, "Where are we, Cap'n?"

"South the bridge."

"How deep is the water?"

"Just down to the bottom."

"MARIO -- He used to race flat track at Old Dominion Speedway. Then he bought a boat. First thing he did was install twin diesels. Second thing was remove the mufflers. Now when you are howling 30 miles out to the fishing grounds you understand what it's like to be awakened before dawn for electroshock therapy.

THE DISPATCHER -- He spends all his time on the radio.

"Cap'n," you say, "this fish is ready. Got the net?"

"Just a minute, son." He grabs the mike. "Salty Dog to Hurricane, come back Cap'n Fred comes back.

"We got one on here south of the Gooses in about 40 feet, pulling metal. Been slow this morning, but I'm seein' specks on the meter. Just now feeding, I guess. Some days, you know. How you-all doin' down south?"

"Captain, he's getting away . . ."

"Sorry, Fred, I got to go. I got some novices aboard . . ."

THE GRUMP, A. K. A. MORNING MOUTH -- Last night he was the sweetest guy you ever met. He bought you a beer, talked about all the fish he'd caught. You booked for the morning and went home. He didn't. Now it's 5:30 a.m., and 1 a.m., when they closed the bar, wasn't long enough ago. Relax. About noon he'll regain civility. If you survive.

THE FISH HOG -- Your're a fisherman? Fine, so's he. Any fish you catch he's going to try to match, and in the end he expects to outdo you. Sometimes the fish hog will get so far ahead he'll stop and explain what he's going to help you out. Unless he establishes that margin, he will keep the mystery intact (see "the Clam").

Once I fished the upper Bay with a fish hog and didn't catch a thing for three hours. Then I caught a striped bass. I was thrilled. The captain promptly pulled out his rod, dropped a piece of bait over the side, let it drift astern and set the hook on a striper exactly one pound bigger than mine. Then he put his rod away.

THE NITPICKER -- When a captain tells you not to put your feet on his fish box, or follows you around with a mop washing down everywhere your feet touch, or charges you for a lure because a bluefish took some paint off it, or cuts off his depthfinder to save the bulb, or keeps fishing the same barren spot even though the radio is cracking with reports of rampaging fish 10 miles away, or provide coasters for your beer, chances are his attentions are slightly misdirected. A boat should be neat. But not an operating room. a

THE SLOB -- He keeps a 50-gallon trash can on the boat into which he insists you throw the paper towels, beer cans, sandwich wrappers, etc. At the end of the day, before starting for home, he carries the trash can to the stern and deposits the contents into the Bay.

These are other undersirable captain types -- The shrieker, the nervous NELLIE, THE BAIT COUNTER, and so on. There is only one kind of desirable captain, and that is a fellow with the skill of a surgeon, the patience of a priest, the sociability of a professional host, the teaching abilities of a professor and the boat-handling skills of a circumnavigator.

You wouldn't think there would be many like that. You don't get rich running a charter boat. But oddly enough, there are quite a few good skippers running parties. Most are scraping along, trying to keep the rates low enough that average people can still afford to go.

Every skipper has is peculiarities. Finding one that suits you can take a while. Then again, skippers probably feel the sam way about us.