In normal circumstances Boxhall wouldn't have been expected to lookout as he had navigational matters to attend to.
As far as I can see it Boxhall spent an inordinately long time off the bridge working out the star positions then some compass deviations that occupied him over 2 hours depending on how you interpret his evidence. Certainly took no less that 2 hours till 10pm if not longer.
His answers in the US were sharp and to the point and there is no indication of any illness then.
Most of Boxhall's evidence on day 3 in the USA was totally non committal and evasive, except the exciting bits we know very well. Perhaps we ought to look at again the bits we don't concentrate on and don't know well? The non - exciting bits. (If the moderators want me to start a new thread or re-open an old thread on Boxhall I am happy to do so).
I just don't think Boxhall was quite 'with it' that evening, and a proper analysis of Boxhall and his infirmities might explain a lot. What is beyond despite is that for most if not all of his watch that evening he was definitely not on the bridge on look out, when extra 'eyes' might have been expected from the Officers.
From what we know of the bridges of other ships, Titanic singularly failed to plan ahead that night.
When Captain Lord saw the ice field he had Groves on the flying bridge with him plus an extra man in the forecastle head (the sharp end of the ship pointing forward).
(It is interesting to note that Evans and Durrant ought to have overheard the Mesaba message but Durrant made no record of it, and Evans didn't either).
When the ice berg was sighted on Titanic, the only officer on the bridge was Murdoch. Moody was in or adjacent to the wheel house, and Boxhall was either exiting the officers quarters or having a cup of tea in his cabin (the two are not incompatible I suggest).
You couldn't make this up!
Cheers,
Julian