In relation to right of way boating rules
And considering a row boat is a vessel as are windsurfers and kitesurfers.
Should SUP's also be considered Vessels and thus be under the control of RoW rules?
Why do you ask? Under what circumstances could it possibly matter? (apart from crossing shipping lanes and going into restricted areas)
A raceboard going full pelt with a tailwind can barely get up to the 5 knot speed limit let alone exceed it.
Yes, all SUPs should have little green and red flags, compulsory flares, torch and 2-way radio. Also it should be essential for the SUP to either tow a back up dinghy or carry an inflatable just in case you hit an iceberg and your SUP sinks.
Also all SUPs should have to have a vessel number and the operator needs to be forced to wear fingerless gloves, lycra pants and a fanny-pack filled with carbo-shots.
Eventually, this world will be a safer place for us all.
Interesting discussion, again immediate reaction is no, however in some circumstances maybe they should.
It should probably be based on length, ie, there is little point in a 8 foot surf SUP being classed as a vessel as it is much closer to a surfboard. A 14 foot or 17 foot Downwind race board which can travel along at more than 8 knots in the right conditions maybe should be a vessel, all gets a bit grey really.
On second thoughts, No, they shouldn't be, it's just too hard 
DM
Yes they do the same as a canoe however for the RoW to come in to play the vessel needs to be traveling at a speed greater than 5 kn depending on what state you live in .
Not that it really matters but from a strictly legal point of view under the international regulations for preventing collisions at sea a vessel is deemed to be any water vessel or any object that can be used for transportation on water, so by this logic even a surfboard is subject to the laws.
