Hello Hamlet, and welcome to the forum.
Records of the marines are not my area of expertise, and there are other members who can probably help you more with that, but I can give you some more information on David Chalk from the Ayshford Trafalgar Roll which should help:
Birthplace: Thatcham, Berks.
Aged 23 in 1805
Date of Enlistment 19 Apr 1800
Trade on entering the Service Labourer
Height on entering the Service 5’ 4”
Joined Ship 31 May 1805
Portsmouth Division Company 83
Prize Money Awarded Prize Money of £1 17s Bd
Granted a Parliamentary Award of £4 1 2s Gd
Died 20 May 1810: Illustrious
Hair: Dark Brown
Complexion: Fresh
Eyes: Blue
How does that match up with your family background, or does his death in 1810 put him out of the running?