Merchant marine working overseas

About 90% of my time working is travelling overseas on a container ship to ports in countries such as Spain, Egypt, Africa, India. A small amount (about 10%) is on the east coast of the U.S. going up and down the coast. How does this get reported and can it help my California State amount due/filing as my company does not withhold California state taxes. My employer is based in Norfolk, VA. Can it also help lower the amount due on my Federal taxes?