I think Lillian is correct. The ship is essentially under martial law, though it doesn't appear to be an oppressive or strict one. From Wikipedia, I pulled this on military non-judicial punishment:

[quote]Punishment can range from reprimand to reduction in rank, correctional custody, confinement on bread and water/diminished rations (aboard ships only), loss of pay, extra duty, and/or restrictions. The receipt of non-judicial punishment does not constitute a criminal conviction (it is equivalent to a civil action), but is often placed in the service record of the individual.[/quote]

More severe crimes (such as murder and rape) would probably tried through a military tribunal.