My daughter Jennifer was all excited when I told her we were going over to the Eastern Shore to do some crabbing. I was a little excited myself, for this was not going to be any ordinary family crabbing expedition. This time we were going out with a real waterman, aboard a real commercial crabbing boat, the Lady-D out of Easton.

Captain Rennie Gay earns his livelihood from the bounty of the Chesapeake. His life evolves around the pursuit of crabs, fish, waterfowl and oysters. Rennie is a young member of the disappearing breed of full- time watermen. A couple of years back, after some prompting from several waterfowl hunters he was guiding, Rennie decided to offer a charter service for sport crabbing, similar to the traditional fishing charters and at about the same price.

When a friend told me about it I couldn't resist. Our family is not all that experienced at catching crabs, but we're no slouches when it comes to eating them. My wife says I've gorged on so many steamed crabs that I'm beginning to walk sideways. Rennie's charter service seemed the perfect way to enjoy a day on the water and come home with more than a tan.

Jennifer's enthusiasm slumped slightly when she learned that we'd have to get up at 2:30 a.m. in order to be aboard by 4:15. But a youngster of 13 is ready for most anything, and I was surprised to see how quickly Jennifer and her friend Laura turned out in the wee hours.

We were fifteen minutes late and the rumble of the Lady-D was already echoing across the still waters of the Tred Avon River. Conversation doesn't come easy in the final hours of darkness, and it was a quiet crew that watched the shadowy shoreline slip past.

The smells, sounds and sights were all new. Nostrils twitched at the mingled odors of diesel fuel and salt eels. Ears listened to the tune of the droning engine and caught the sound of others somewhere out there in the blackness. The girls huddled behind the cabin along the port side, hiding from the morning chill.

Several miles downriver Rennie throttled back and eased Lady-D close to the shore to lay out the trotline, one of the oldest and most efficient methods of taking crabs. It's a long line, anchored at each end, with baits attached every two to five feet. A sport crabber might use a trotline of two or three hundred feet, dipping the crabs as the baits are pulled to the surface.

Working quickly and efficiently, Rennie and mate Bob Bradley put out a 3,000-foot trotline and another of 2,500 feet before the sky revealed much more than a faint glow of pink. With the pieces of salted eel about three feet apart, I figured we had nearly 2,000 baits in the water. The girls watched widening eyes. This crabbing trip was going to be something more than dropping a few handlines over the side.

With the lines out and the sun beginning to show its face, the fun part -- he dipping -- was about to begin.

Rennie netted a few to show the technique and explained that we should try only for the ones that looked to be legal: five or more inches from point to point. "OK, now it's your turn," Rennie said. "Who's first?"

Laura stepped right up, took the net and caught the first crab that came up the line. With a quick heave she swung it aboard and into the sorting box. "Nice job," Rennie said, "but you better net five or six crabs before you dump 'em in the box. Three more came up and dropped off the baits whilst you was landin' that one."

After a few minutes Laura had it down pat. When Jennifer took over she caught on just as quickly. The girls kept Bob busy at the sorting box, checking for size and separating out the "blues," those with the hardest shells and most meat. "Whites" are not quite as heavy and are slightly softer.

In the commercial market the blues bring the premium price. Sorting them properly is an important job and, as Rennie puts it, "The only difference between a blue and a white is your conscience." We really didn't have to sort our crabs, but we had decided in advance to do everything the way the watermen do it.

After a couple of hours the girls decided it was time for lunch. It was only nine o'clock, but we were hungry just the same. Then it was sunbathing time for the girls. I couldn't blame them; the warmth of the morning sun was an agreeable change from the cool air of dawn. Afterward the hours slipped by all too quickly. When Rennie and Bob began pulling the lines there were 10 bushels of crabs on the deck, along with three tired crabbers.

Rennie crabs commercially every day during the season, except for those days he takes out sport crabbers.

"It ain't jest the crabs that brings people down here," he said. "Folks seem to be fascinated with the life us watermen lead. Other folks just love to be out here when the sun comes up. Can't blame 'em, either. They come aboard with big coolers full of food and beer and soda. Most of 'em seem to have a pretty good time." TO GRAB A CRAB

If you would like to live the life of a waterman for a day, contact Rennie Gay, RD 5, Box 25, Easton, Maryland 21601. Telephone 301/822-0413.

To run a trotline more than 100 yards long requires a sport-crabbing license, which can be purchased (by Maryland residents only) for $5, in person or through the mail from the Department of Natural Resources, Box 1869, Annapolis 21404. Telephone 301/269- 3211 for information. Licenses are also available from county court clerks. A license- holder can take three bushels of crabs. For those under 14 or over 65 there is no fee, but a license still must be obtained.

Gay can handle up to six crabbers, and the fee is $250 whatever the size of the party. Clients can take home all or any of the catch. If everyone has a license, including the captain and mate, the total legal catch is 24 bushels. The average catch is more like six to ten bushels but he managed to boat 65 bushels one day last September.