Originally Posted by Paul Barnard

Everything I wrote is 100% correct. It seems to me that you may unwittingly conflating several of the rules. I said a vessel cannot be restricted in its ability to maneuver (RAM) on account of it's size. Your post above counters that by speaking to constrained by draft. They are separate restrictions in the rules and purposefully so.

It is the nature of a vessel's work that will make them RAM. Constrained is used in only one context in the Navigation Rules. Constrained by draft. That applies only in international waters not in inland waters. A vessel is never "restricted in its ability" to maneuver on account of size, draft or dimension. A vessel can ONLY be restricted in its ability to maneuver on account of the nature of its work.

Here are a few definitions from RULE 3 International: Constrained by draft isn't defined in the Inland Rules. The RAM definition definition is identical in the Inland and International rules.

(h) The term “vessel constrained by her draft” means a power-driven vessel which, because of her draft in relation to the available depth and width of navigable water is severely restricted in her ability to deviate from the course she is following.

(g) The term “vessel restricted in her ability to maneuver” means a vessel which from the nature of her work is restricted in her ability to maneuver...


Rule 9 is the narrow channel rule. It is here that size (length) matters.

(b) A vessel of less than 20 meters in length or a sailing vessel shall not impede the passage of a vessel that can safely navigate only within a narrow channel or fairway.This is where we see length come into play.

https://www.navcen.uscg.gov/pdf/navrules/navrules.pdf