3 watch rule

I am trying to determine the requirement for establishing a 3 watch rotation on a voyage greater than 600nm. There is a clause in 46 CFR 15.705 that states “The Coast Guard interprets this, in conjunction with other provisions of the law, to permit licensed masters or mates (pilots) serving as operators of towing vessels that are not subject to the provisions of the Officers’ Competency Certificates Convention, 1936, to be divided into two watches regardless of the length of the voyage.”

How can I determine if we are subject to the Officers’ Competency Certificates Convention, 1936?

A little more research provided the following (which makes things even more confusing for me):
“The Officers Competency Certificates Convention, 1936 (International Labor Organization Draft Convention Numbered 53, on the minimum requirement of professional capacity for masters and officers on board merchant vessels), as ratified by the President on September 1, 1938, with understandings appended, and this section apply to a documented vessel operating on the high seas except
(1) a public vessel;
(2) a wooden vessel of primitive build, such as a dhow or junk;
(3) a barge; and
(4) a vessel of less than 200 gross tons as measured under section 14502 of this title, or an alternate tonnage measured under section 14302 of this title as prescribed by the Secretary under section 14104 of this title.”

The CFR states that a vessel greater than 100 tons must adhere to the 3 watch rotation but later in the same section it says that vessels subject to the above are exempt from the 3 watch system. So what if the vessel in question is between 100 & 200 tons?

I’m not certain but I believe it has to do with operating outside the Demarcation Lines. If you don’t cross the line the rule doesn’t apply…
Here’s a link to the Regulation… http://uscode.house.gov/download/pls/46C83.txt
From Joel Milton’s research
And some more reading

So if I read it correctly, 46 CFR 15.705d states than towing vessels of less than 200GT are allowed a 2 watch system regardless of length of voyage (and regardless of area of operation). Thanks for the link to the policy letter. I guess the good news is we won’t have to hot rack!