I’m pretty sure you can’t upgrade to 2/M AGT on tug time.
because you mentioned “married” and a 100k bbls barge, I’m assuming ATB, so you have this to consider:
46 CFR 11.211 (d) - [I]Service on a Dual Mode Integrated Tug Barge (ITB) unit is creditable for original or raise of grade of any deck officer endorsement. Service on a Dual Mode ITB with an aggregate tonnage of over 1600 gross tons is creditable on a two-for-one basis (two days experience equals one day of creditable service) for up to 50 percent of the total service on vessels over 1600 gross tons required for an unlimited officer endorsement. The remaining required service on vessels of over 1600 gross tons must be obtained on conventional vessels or Push Mode ITBs.[/I]
conventional ATBs (intercon, bludworth, jak, etc) are dual mode. NVIC 2-81. This CFR basically shoots down any assumptions one might have about aggregate ATB tonnage and unlimited seatime. They do throw you a bone, but not much. The way I read it together with 11.402, is that ATB time can count for basically 25% of you unlimited time (half of the required >1600T time, which must be half of you total time). Correct me if I’m wrong. Otherwise you’d be able to upgrade on ATBs and that almost certainly isnt the intention.
Then theres 46 CFR 11.402 (a) - [I]To qualify for an ocean or near coastal endorsement for vessels of any gross tons, all the required experience must be obtained on vessels of over 200 gross tons. At least one-half of the required experience must be obtained on vessels of over 1600 gross tons.[/I]
so you can get 75% of your time, (half of the required 1600T time being on an ATB), 50% on vessels 200-1600T, but you still would be looking for 90 days on a true >1600T oceans vessel.
As far as 1600T Masters, without having a 2/M and taking the limited exam, the other way to do it is this:
[I]46 CFR 11.412 Service requirements for master of ocean or near coastal steam or motor vessels of not more than 1600 gross tons.[/I]
[I]The minimum service required to qualify an applicant for an endorsement as master of ocean or near coastal steam or motor vessels of not more than 1600 gross tons is:[/I]
I Four years total service on ocean or near coastal waters. Service on Great Lakes and inland waters may substitute for up to two years of the required service. Two years of the required service must have been on vessels of over 100 gross tons. Two years of the required service must have been as a master, mate master or mate (pilot) of towing vessels, or equivalent supervisory position while holding a license or MMC endorsement as master, mate, master or mate (pilot) of towing vessels. One year of the service as master, mate, master or mate (pilot) of towing vessels, or equivalent supervisory position must have been on vessels of over 100 gross tons; or,[/I]
I An applicant holding a license or MMC endorsement as chief mate or second mate of ocean or near coastal steam or motor vessels of over 1600 gross tons is eligible for this endorsement upon completion of a limited examination.[/I]