Robert Stubbs had captained a slave ship several decades earlier .
Robert Stubbs temporarily commanded Zong during Collingwood 's incapacitation , but Robert Stubbs was not a registered member of the vessel 's crew .
Robert Stubbs had captained a slave ship several decades earlier and he temporarily commanded Zong during Collingwood 's incapacitation , but he was not a registered member of the vessel 's crew .