Upgrading from Tankerman PIC barge to regular tankerman endorsement?

I am a going to be a deck cadet this summer on a fuel ATB and want to know the difference between the endorsement I receive through an ATB and a regular endorsement. Can they be interchangeable, what is the process to upgrade to the regular tankerman endorsement? Which one is more valuable?

The tankerman - ship is more valuable since it supplies to barges as well. I am fairly certain the only way to upgrade is to do the 90 says on a tank ship and get your ship loads and discharges.

OK thanks. I’m going to do all I can to get on a tankship. I’m planning on shipping with US Shipping which has several very old product tankers. Would that be recommended over one of their newer ATBs which I’m scheduled to ship on currently?

If you get your time on a ship you will get a higher level of tankerman from it than on an atb. Do the math…