Near Coastal waters extend up to 200 nm for Master/Mate and 100 nm for OUPV.
Near-coastal means ocean waters not more than 200 miles offshore from the U.S. and its possessions, except for MMCs endorsed as Operator of Uninspected Passenger Vessel for which near-coastal is limited to waters not more than 100 miles offshore from the U.S. and its possessions.
This means your Master or Mate NC license is valid out to 200 nautical miles; or if you have an OUPV license, it is valid out to 100 nm.

Yes. Any license or MMC endorsement issued for service as master, mate or OUPV on near-coastal waters qualifies the mariner to serve in the same grade on Great Lakes and inland waters, except towing vessels upon western rivers subject to the limitations of the endorsement.
Inland waters are defined as the navigable waters of the United States shoreward of the Boundary Lines, and excluding the Great Lakes. Inland waters include rivers, entrances to small bays, inlets, harbors, and the ends of breakwaters or jetties.
In the hierarchy of Coast Guard waters, inland is the lowest level. Great Lakes is the next higher level, then Near Coastal. A 100 GRT Master Inland is not allowed to operate on the Great Lakes or Near Coastal waters as a 100 GRT Master.
Because you hold a Master 100 GRT Inland under 46 CFR § 11.457 you can take an "Upgrade" course from Master 100 ton from Inland to Near Coastal. These are short classes and they cover two USCG tests for you: Q150 - Deck General and Q152 - Navigation General: Oceans or Near Coastal.
If you hold a Master 100 GRT Inland under 46 CFR § 11.457 and want to become a Master 100 GRT Near Coastal, we recommend taking an Upgrade USCG Approved Course once you have 720 sea days in the deck department, with 360 days on Near Coastal or Ocean Waters.
Before serving as master or apprentice mate, based on current credentials, of towing vessels on the Western Rivers, mariners must possess 90 days of observation and training and their MMC must include an endorsement for Western Rivers.
Yes. You will have to meet the requirements for the towing endorsement for Western Rivers and apply for an Increase in Scope which is also called a Modification.

We hope this made your life a little easier and if you have other questions the MM-SEAS team is always here to help!
MM-SEAS is free to use on your own and if you need some more personalized help you can upgrade to MM-SEAS Expert Access inside of the site.
No matter what, when you are ready to submit your application you can do it yourself, or you can hand the whole thing to us. An MM-SEAS Navita Navigator walks you through submitting in Navita, the Coast Guard's new submission portal, on a short video call. No computer, or not up for a video call? Our team gets your application submitted to the Coast Guard for you anyway. A Stress-Free MMC is $399. Two MM-SEAS licensing experts check every page, we pay your Coast Guard fees at submission and charge your card so you never touch pay.gov, and we stay on it with the National Maritime Center until your credential is issued.
MM-SEAS Expert Access is $99 a year. It is your personal guidance counselor for USCG licensing: what training you need next, which sea time counts, and how to reach the credential you want, by phone, email, chat or a 1 on 1 video call. Expert Access members also get $50 off a Stress-Free MMC.
Nate Gilman is President and Co-Founder of MM-SEAS. He hawsepiped from the deck to a 3rd Mate Unlimited license with full STCW compliance over more than 15 years at sea, and is a veteran of the NOAA Commissioned Corps. He works directly with the National Maritime Center, USCG-approved training schools, and vessel operators on credentialing policy, and writes on sea service documentation, evaluation standards, and how mariners move up the license ladder.