Seafarers with dual exam can obtain a certificate of competency as a dual ship officer.
To renew or upgrade this, seagoing service must be obtained in a dual position onboard.
If you do not obtain seagoing service in a dual position, the seagoing service is obtained as a navigator or engineer, and the required amount of seagoing service thus follows the general requirements for navigator and engineer certificates.
If you have certificate as dual, but do not serve as dual, or obtain sufficient seagoing service as a navigator or engineer, you will not be able to maintain the dual certificate.
If you serve exclusively as a navigator, you will be able to maintain the lowest level as an engineer, watchkeeping engineer, in your dual certificate.
If you serve exclusively as an engineer, you will not be able to maintain the navigator part of your dual certificate.