"We had heavy rain overnight in both games so that didn't make it easy," said the former Bay senior men's representative coach.
During the Bay senior men's club competition and the Bay secondary schoolboys' first XI league, NBHS had accrued 20 wins from 29 matches.
Nelson College are the CD qualifiers for the annual New Zealand Secondary Schools' Cup (formerly Gillette Cup) to be staged in Christchurch in December after beating New Plymouth in the final.
"It's taken Napier Boys a long time to build a nucleus of players."
Cotterell singled out three players for special mention after the season.
Captain Todd Watson, a CD U17 rep, scored 733 runs, claimed 54 wickets and took 10 catches.
Middle-order batsman Daniel Shartlin carved up 500 runs and claimed 43 scalps as a medium pacer.
Offspinner Nick Hutton claimed 47 wickets.
All three are Bay under-17 representative players.
Cotterell said left-arm swing bowler Robbie Brigham also had a tidy season.