Unlike last weekend's sailboat show, which was a show-and-sell venture all the way, the powerboat show that starts today at the Annapolis city dock and harbor makes a special point of giving its ticket buyers a chance to learn something. Demonstrations, seminars and movies that are supposed to provide special insights for area fishing aficionados will be a daily feature of the four-day event.

Today, for example, three charterboat captains will hold forth on the making of bucktails, how to get drumfish out of the middle bay and the best approach to fishing Tangier Sound.

In the three other show days, substantial erudition will be cast on such diverse subjects as how to fish the cripple alewive, taxidermy, the use of a depth finder to find fish, the basics of trawling and how to build your own rod.

Not that those who want to buy a boat will find any faults with the 250-boat collection.

At the top of the price list is a Hatteras 60 convertible for $600,000. It has three lavishly furnished state-rooms (each of which has individual air conditioning, heating and stereo controls), and enclosed flying bridge, two other control stations and an engine room so large one can stand up to both admire and work on the twin 650-horsepower engines.

The galley compares with the kitchen of a Georgetown house: Two ovens (one microwave, one conventional), a four-burner range, dishwasher, garbage disposal, washer and dryer and a 19 cubic foot refrigerator.

Even more impressive in its appointments is the Pacemaker 66 cruiser. The boat-show model lacks some of the expensive electronic equipment on the shorter Hatteras and cost only $515,000. For that commas one gets a salon, a dining room, four staterooms - one designated for the crew - and lots of pictures, drapes, carpets, cedar-lined closets and beautiful furniture. All it lacks is a grand piano and a Rembrandt.

A special area in the show is reserved for the economical trawlers. Less plush than some of its neighbors but also less expensive is the Prarie 29. It sleeps five and has a 50 horsepower diesel that uses little more than a gallon of fuel per hour and provides a 600-mile cruising range.

"It doesn't have the wood trim of some of the others," says salesman Jerry Hawk. "Wood does improve the appearance, but it requires a lot of upkeep. We left it off to keep the cost down." The boat is priced at $32,000.

Not at all run-of-the-mill is the 14 1/2-foot fibreglass airboat being shown by Paul McCoy of Severna Park, Md. The thing is pushed by a 25-horsepower motor that turns an airplane propeller attached to the stern.

"I had it made to commute between my home and Annapolis," says McCoy. "It turned out to be a little impractical for that but it'll do 25mph and it's lot of fun."

Show hours today through Saturday are 10 a.m. to 7 p.m. Sunday, the show opens at 10 a.m. and closese at 6 p.m. Tickets for adults are $5; children (12 and under) pay $3. Parking at the Navy Stadium on Rte. 70/Row Boulevard costs $2. Shuttlebus service to and from the show is free.