Quoting Farwell's Rules of the Nautical Road's summary on lookout's:
A lookout has been defined by the federal courts as a person who is specifically charged with the duty of observing the lights, sounds, echoes, or any obstruction to navigation with that thoroughness which the circumstances permit. The statement in Rule 29 and Article 29 (now Rule 2) that nothing in the rules shall exonerate any vessel from the consequence of any neglect to keep a proper lookout has caused the courts to hold a vessel in collision without a proper lookout at fault unless it can be proved that the other vessel was discovered as soon as a proper lookout would have discovered her.
Numerous court decisions have built up a considerable doctrine with reference to what constitutes a proper lookout. Such a lookout must have no other duties, such as conning or steering the vessel; he must be constantly alert and vigilant, he must have had a reasonable amount of experience as a seaman; he must report what he sees or hears to the officer of the watch; and he must ordianarily be stationed as low down and as far forward on the vessel as circumstances permit. In conditions of crowded traffic and in thick weather enough lookouts must be posted to detect the approach of another vessel from any direction.
It's worth noting that the gimmick of single-handing ocean crossings is a relatively new, as well as a former rare practise, and it's highly doubtful that it will receive a kind ear in a court of Admiralty. You'll likely be convicted on the prima facie evidence alone; if you're single-handing, you cannot maintain a proper lookout. You'll note that steamship companies, whose manning level on each class of ship is approved by the USCG, are still liable should that manning level prove unsufficient in the event of an accident. And that was the real lesson from the Exxon Valdez incident; inadequate manning resulting in fatigue of the officers.
“Scientists are people who build the Brooklyn Bridge and then buy it.”
Wm. F. Buckley, Jr.