An inland 1[mechanically propelled vessel] having engines of less than 2[forty] nominal horse-power shall not proceed on any voyage unless she has—
(a)as her master a person possessing a scrang‟s certificate granted under this Act, or any certificate referred to in clause (a) of section 26, and
(b)as her engineer a person possessing a second -class engine-driver‟s certificate granted under this Act, or any certificate referred to in clause (b) of section 26:
Provided that a 1[mechanically propelled vessel] shall be deemed to have complied with this section if she has as her master and engineer a person possessing both a certificate referred to in clause (a), and a certificate referred to in clause (b), of this section.