Will people shell out $250,000 for a boat designed by a rock star?

The answer will be known in three weeks when the 38-foot Shelter Island Runabout, a product of singer Billy Joel’s lifelong fascination with the sea, is unveiled at a Newport, R.I., boat show.

Until now, glimpses of Joel’s vision of an express cruiser for day trips – fleshed out by a Massachusetts yacht designer and a Shelter Island, N.Y., boatyard – have been limited to drawings in boating magazines. But that has generated enough interest in what looks like a cross between a Maine lobster boat, a PT boat and a Prohibition rum runner to keep the phones jangling at Coecles Harbor Marina and Boatyard on Shelter Island for the past six months.

“The response has been overwhelming. I’ve got a book filled with names from all over the world,” boatyard co-owner Peter Needham said. “And I haven’t done any advertising. Most people want to see the finished product, which will be christened at the Newport show. I have a feeling that it’s going to be a huge success.”

The first Shelter Island Runabout is getting its finishing touches in a shed at Coecles Harbor. The boat, Nomad, will be kept by Joel, who will help market the design at Newport and other shows.

Needham expects to hire 15 craftsmen to augment the eight who completed Nomad and acquire a second construction site if the orders warrant it.

The rakish 38-foot-5 modified deep-vee hull is expected to be propelled at a top speed of 55 mph by twin 415-horsepower Mercruiser stern-drive engines. Several manufacturers have started to make similar boats, Needham said, but none will achieve speeds close to Nomad’s because of its large engines and light and strong Kevlar hull.

Joel plans to keep his current boat, the 36-foot Alexa, which was inspired by a swordfishing boat and was also built by Needham’s yard, for fishing and longer trips year-round.