RBBB can be due to serious problems and needs to first be investigated. IF the cardiologist can find no serious problems, then you are termed as having a normal variant and it can basically be ignored. The signal coming down the His bundle should divide into the left and right branch. Your right branch is not accepting the signal and so it only goes down the left bundle into the left ventricle. The signal eventually finds its way through tissue to the right ventricle but there is a delay, meaning the left and right ventricles are not pumping at the same time. If there isn't TOO much of a delay, then this is not a real issue.
Such problems your cardiologist would be checking for are pulmonary embolus (blood clots in the lungs), lung disease, cardiomyopathy, atrium/ventricle septal defects.
So until all possible serious causes are eliminated, I think your cardiologist is correct in saying you are not fit for sea duty.
Right Bundle Branch Block (RBBB) is NOT a serious disease and there is no cure. It is rarely of any medical significance. It is a blockage in the electrical nerve bundle on the right side of your heart that signals the heart to beat. The heart compensates and finds an alternate route. This is a fairly common finding and most people that have RBBB don't even know they have it as there are no symptoms. The only time it needs to be watched or poses any concern is in the presence of coronary artery disease.
I'm surprised this would affect your employment as it truly has no effect on your life. Perhaps a note from you doctor concerning your overall health would help.
Hope this helps,
Jon