This appears to be your Robert MANSFIELD
Embarked Plymouth 21 July 1851 on the MINDEN and arrive Fremantle on 14 Oct 1851.
MANSFIELD Robert
Reg# 914 Term 7 years Age 18 [The age quoted seems to refer to the age of the convict when the passenger list was created.]
Trial place - Wells Date 27 03 1849
Criminal Offence -Larceny
Physical description - 5'2" Hair black, eyes hazel, face oval, complexion - swarthy, build stout.
The marriage in 1857 is possible as Robert would have completed his 7 year term. Hopefully the marriage certificate will have Robert's age at the time of marriage.
Cando