In answer to my question in last Saturday's post Mike B send me this:
This is regrettably we should have an answer to, and so it should be considered at some length.
The place to start (as always) is with the definition.
Here we have the unusual words “could not pass” no reference to damage, or seamanship, these are in other definitions and rules.
Clearly these cats probably could pass the buoys, even if they scraped over them, if this is the case then they are not obstructions.
The lighter the wind (so the boat has both hulls in the water) and the lower the freeboard the more there is a possibility of the boat being unable to pass over the buoy and the more there is a possibility we would have to consider them as obstructions.
If the cat could not fly over them my maths would indicate a substantial alteration of course would be required. Simply the best answer is to specify in the sailing instruction as to whether these buoys are or are not obstructions.
This gives us an interesting little window on the rules themselves which may be worth the journey.
Here the right of way boat probably has no problem, it is a give way boat who may have the requirement to claim “room”.
Now as soon as room is claimed the “seamanlike way” becomes operative. Hulls in the water with low freeboard, then probably you should avoid the buoy so yes to obstruction and yes to room.
If you are flying a hull, then little course alteration and little in seamanlike problems, so no to obstruction and no to room being much at all.
What then if you were forced to fly a windward hull over a buoy, I would say this was OK.
If you as windward boat boar off and made contact with the leeward boat, you could only be exonerated under 64.1.c. If you could fly a hull can you really say you were “compelled”? Another of this rules complications.
Now look at the difference in the rules, you cannot hail unless “safety requires her to make a substantial course alteration” a big test, and unlikely to be met.
So no Rule 20 and Rule 19 possibly but be very careful, and this is even if you do call the buoy an obstruction.