USCG boating-safety resources identify carbon monoxide as a potentially lethal boating hazard. Exhaust can collect near swim platforms, enclosed cabins and canvas-covered spaces.
Maintain engines, generators, exhaust systems and alarms; keep people away from exhaust outlets; and respond immediately to headache, dizziness, nausea or confusion.
Move affected people to fresh air and obtain emergency help. Do not assume ventilation or an open hatch makes an occupied space safe.