At the 18th annual Washington International Boat Show you can get your eyeglasses cleaned, subscribe to a magazine, watch a grown man scuba diving in a tank of water the size of a shower stall, see the official 1978 Indianapolis 500 pace car and register for a free hauling out and bottom painting.

You also can buy a boat.

The show ends a week long run at the D.C. Armory/Starplex with an exhibition today from 1 p.m. until 8 p.m. It is geared toward the sales of aquatic transportation, but by no means is that its only fare.

Sales representatives are equipped to provide all the nautical necessities, from bikinis to batteries. The Coast Guard will lecture you on safety, the National Oceanics and Atmospheric Administration will advise you on the weather and somebody might even try to sell you a hot tub or a Swiss workbench vise.

The main attraction, however, is the boats. There are more than 500, ranging from canoes to cabin cruisers, all available for purchase.

The salesmen, disappointingly, are not of the "old salt" variety. You can look for a weatherbeaten face under a waterman's cap but there aren't many graybeard-and-pipe types around. Most look as if they would be as comfortable selling insurance or automobiles.

An exception, however, is Peter Carroll, show codirector. At least he has a gray beard and is a man with whom you can feel comfortable whether you decide to fish or cut bait.

"What a boat show? Well, it's convenience shopping," said Carroll, now in his third year with the show. "You get 65 or 70 dealers and they bring in the boats that they want to merchandise. The customers get to see the highlights of the local dealers' lines all in one place. Its an economical way to shop."

The blizzard of '79 has threatened the economics of this particular effort. After an impressive opening last weekend, the snow kept the portals closed on Monday. Lack of Metro operations severely curtailed attendance on both Tuesday and Wednesday.

Despite its weather, Carroll finds Washington a good place to put on "the biggest boat show between New York and Miami."

"Washington is a good market for boats for the same reasons it's a good market for anything," said Carroll. "It has stable employment, good salaries and a lot of families in which both husband and wife work."

Although the market has been steady for boats in the Washington area, some of the trends in purchasing have changed.

"The average customer is looking for an all-around boat," claimed Steve Fischer of the Rockville Boat Center. "By that I mean he wants a boat in which he can go cruising with the family, ski and have room to take out his friends. The trend is away from the high performance boat to the smaller runabout type."