With the high humidity and cold temperatures, in addition to the poorly insulated wooden ships
Im assuming burning fuel for heat wasn't common because of the fire risk and the inconvenience of hauling coal/charcoal. Ive never heard of a pre-steam engine ship running out of fuel
This would make it lethally cold, how did people survive?
The answer is pretty basic, really: ships would have a galley stove and often a small stove in the wardroom (where the officers gathered) that would warm the space. Sailors would wear oilskins to prevent getting wet, and wool clothes that keep you warm even when wet. Space and crowding was also something that would take care of some of this for people -- in the Royal Navy, sailors were allocated 14 inches of space (width) to sling their hammocks. In practice, only half or one-third of the crew was off watch at a given time, so they would have 28 inches of space, but you can imagine the amount of heat produced by several hundred sailors sleeping cheek by jowl.