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Trans-Atlantic passenger travel was not very popular until the advent of the steamer, and yet men and women crossed the ocean periodically, including the affluent.

From what I've been able to gather, a fireplace, or even a stove, was unthinkable outside the galley. Sailors may have been used to it, but what about folks who paid good money for the trip and expected it to be somewhat comfortable? Did they just use a lot of blankets in their cabins?

Long ago, in 16 century they used open fire (with all possible precautions) on
the deck to cook (ref. Morison, Admiral of the Ocean Sea). Later they used a galley.
There was no other way to heat yourself, except a lot of cloth, blankets etc.
Yes the travel was not very comfortable, even for the rich.

They rarely traveled in winter by the way,
and for more important reasons than mere cold.

Recently I saw a film in youtube of some re-enactment of a trip of the Vikings
in a replica of a Viking ship. The re-enactment happened in summer, of course,
and they used the modern high-tech cloth. But the ship and its equipment was authentic as much as possible. Several people had to drop from the enterprise,
and they were picked by an accompanying modern boat and evacuated. Because they
could not tolerate cold.

Such stories are abundant. One 20th century re-enactment of the Columbus
voyage had to be abandoned completely because the crew could not endure
the conditions and rebelled. I recall that Columbus own crew was also
on the verge of rebellion when America was finally discovered.

My general impression is that people were tougher, and could endure more hardship then most of modern people. (And more people died from various reasons, of course.
In particular during the sea travels.)

Remark. I traveled in the North Atlantic myself, in a sail boat, in summer. There was no heating, of course. It was difficult to stand a 4 hour night watch, in ordinary cloths without a special modern high-tech sailing suit. But it was OK to sleep in a sleeping bag in a cabin.