Everyone knows !
'restricted in ability to maneuver' is a very precise defined term - and does NOT just mean a 'big vessel' nor 'the bigger vessel'. Depending on the situation, a supertanker can perfectly well be the give way vessel to a small sailboat (although it would be polite for the sailboat to let the super tanker proceed directly).
The definition: "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 as required by these Rules and is therefore unable to keep out of the way of another vessel." That means things like dredging or a tug boat with a tow (and not just any tow but one which "severely restricts the towing vessel and her tow in their ability to deviate from their course". Again it does not simply mean a big vessel. There is a lot of precedent on this specifying what specific 'nature of work' provides 'restricted in manoeuver privileges.
There are also rules related to situations where one vessel is 'restricted by draft', which is often a big vessel in a channel, but can be a very deep keeled sail boat also. Again, is very precise and not 'just a big vessel'.
And there are rules related to vessels in traffic controlled zones, which do generally allow large vessels to proceed unimpeded by small vessels. but they only apply in specific traffic controlled zones, and interestingly if the risk of collision occurs then the normal collision regulations switch on and there is again absolutely 'no rule of tonnage'.
Bottom line: There is absolutely no 'tonnage rule' in marine collision avoidance.
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