(FORTUNE Magazine) – With vacationers in such watery paradises as Barbados, St. Thomas, and Hawaii clamoring to do more for their $300 a day than lie on the beach, why not offer them underwater bus tours? By some estimates, there is a worldwide resort market for about 100 tourist submarines. Encased safely within a steel hull the thickness of a cigar and provided with individual view ports, up to 50 vacationers at a time can make like Captain Nemo for an hour before ascending. One manufacturer, Fluid Energy Ltd. of Scotland, has sold nine subs so far at a base price of $2.7 million each and plans to build others with Florida-based joint venturer Nautilus Submarines of America. Another manufacturer, Canada's Sub Aquatics Development, says it pioneered the tourist sub idea in 1983 and has sold five worldwide. ''Now,'' complains vice president Barry Bellchambers, ''everybody and his brother is trying to jump on the submarine bandwagon.'' - A.F.