There are 4 different Masters Licenses a mariner may qualify for such as the Master Inland or Master Near Coastal. Both the amount of sea service time and the size vessels you have been on will influence the license you are eligible for. Masters licenses are tonnage rated at 25 GT (gross tons), 50 GT, or 100 GT. The tonnage you are awarded is determined by the size vessels you've gained experience on in the last 3 years. You are not required to advance through the different licenses one at a time. If you meet the USCG requirements for the master 100GT Near Coastal, you'll get that license as your first license.
The 4 types of up to 100GT Masters licenses are listed below along with the requirements:
Master Inland: 360 days underway experience since age 15; 90 of those 360 days in the last 3 years. Completion of Mariners Learning System approved Course and Test.
Master Inland/OUPV: 360 days underway experience since age 15; 90 of those 360 days in the last 3 years; 90 of those 360 days outside the boundary lines. Completion of the Mariners Learning System Coast Guard approved Course.
Master Inland/Mate N.C.: 360 days underway experience since age 15; 90 days of those 360 days in the last 3 years; 180 of those 360 days outside the boundary lines. Completion of the Mariners Learning System Coast Guard approved Course.
Master Near Coastal: 720 days underway experience since age 15; 90 of those 720 days in the last 3 years; 360 of those 720 days outside the boundary lines. Completion of the Mariners Learning System Coast Guard approved Course.