After some three years of courtship, Cape Air and JetBlue Airways chose Valentine's Day to announce a marriage of customer convenience for passengers to and from Logan International Airport.

Beginning next month, passengers arriving from or departing to 20 destinations across America with JetBlue will be able to connect far more easily with Cape Air flights to the Cape and Islands.

Until now, passengers had to get two tickets, have two boarding passes, recheck baggage and pass through security twice in transferring from one airline to the other.

Under the new arrangement, someone coming from, say, San Francisco to the Vineyard can book both legs of the flight through one carrier, be issued both boarding passes, check bags straight through and change flights in Boston without further security screening.

Like many relationships, the genesis of this one began with proximity, when JetBlue began operating out of the same wing at terminal C at Logan as Cape Air, about three years ago.

"At Terminal C we operate about a dozen gates," said a JetBlue spokesman after the announcement this week. "The only other airline operating in that terminal wing is Cape Air, with one gate. It made sense that passengers should be able to just walk from one to the other," he said.

"Cape Air had one partner now which is Continental, so if you took Continental into Boston you could connect seamlessly, too. The only difference being that we're right there. Essentially, their planes are at our terminal."

Both companies said they expected to carry tens of thousands more customers as a result of the partnership.

Cape Air president Dan Wolf said his airline now operates at around 53 per cent capacity, and he expects it to increase to about 60 per cent. Cape Air currently carries around 700,000 passengers a year.

Flights under the new arrangement will begin on March 19, but can be booked now.

At the same time, JetBlue announced it would begin a new direct seasonal service between Nantucket and New York's JFK International Airport. Service is set to begin on May 24, running daily until Sept. 24.