Re: CO alarm on boats ?
It's a no-brainer: Put one in. Remember, the CO bonds to hemoglobin in the blood, preventing it from picking up oxygen. Bonds as in "does not let go". CO poisoning can effect you for days, and therefore be cumulative (a second dose could finish you off); a simple breath of fresh air helps, but your oxygen pickup (and therefore decision making, coordination, etc) is still compromised until it has been flushed from your system.
In a house it's a good idea; in an enclosed small volume like a boat, it is a no-brainer.