Floating publicans and fishing crews shouldn't experience too many headaches over the smoking ban - once they are over 12 miles offshore.
The law may not apply on the high seas outside the territorial limit, according to marine sector representatives.
"We have enough problems anyway without having this one to contend with," Lorcan O Cinneide of the Irish Fish Producers' Organisation (IFPO) commented.
Fishing vessels are both workplaces and domestic environments and, as such, may be subject to the ban in inshore waters.
However, the Department of Communications, Marine and Natural Resources has given no special direction to the industry, Mr O Cinneide noted.
Nor has the Naval Service been asked to police the smoking ban within 12 miles. "Our primary role is fishery protection, and our powers are confined to a limited area of legislation otherwise," Lieut-Cdr Gerry O'Flynn, Naval Service spokesman, told The Irish Times.
The majority of vessel boardings undertaken as part of fishery protection duties occur outside the 12-mile limit in any case, he pointed out.
Smoking is "almost gone" on Naval Service ships, under measures introduced several years ago, Lieut-Cdr O'Flynn said. "It has been confined to very designated upper deck areas for some time," he said.
However, some passenger ferry companies are awaiting clarification from the Department of Health and from the Health and Safety Authority on the new legislation.
"We have been in touch with both bodies but no one has come back to us," Mr Eamon Hewitt of Stena Line said.
Until such guidance is provided, there will be no change to current arrangements on his company's ferries, he said.
"Smoking is only permitted on the high speed catamarans [HSS\] on deck, but we have designated smoking areas in the bars and restaurants on the conventional ferries," Mr Hewitt said.
Stena's fleet is registered under the British flag, however, and it has staff employed in Britain.
"There is a questionmark as to whether this can apply to ships which do not sail under the Irish flag."
P&O Ferries is also registered under the British flag, while vessels with Irish Ferries are on the Irish register.
A spokesman for Irish Ferries said that it intended to implement the ban fully on its vessels.
Ferry companies believe the ban could prove difficult to enforce at sea.
"You can't exactly ask someone to leave a ferry nor can you call the gardaí when you are off the Tuskar Rock," one company source quipped.