As a couple of others said above, Greyhounds have got to be the laziest dogs
ever when not running.
I used to enjoy going to the Greyhound track when we had one here (state-run video-poker killed the dog-track) and was always amazed at how mild-mannered they were. They would often walk dogs
who weren't running that day amongst the crowd and the little kids
would be pulling their tails, ears, and poking etc... and the dogs just took it without a second thought.
Greyhounds enjoy a good daily run, but when not running (99.9% of the time), they might as well be furniture.
BTW, I've never seen a happier dog than a Greyhound when racing
around a track. Very impressive when the pack runs by and several seconds later you hear the "thud-thud-thud, thud thud" of dirt-clods falling back to earth....
Flagler and Hollywood Florida
are still, I believe, two of the nations top dog-tracks. I'd assume they take the heat pretty well? Good point on them not being much of a swimmer though.
I think they'd make a good (albeit not ideal) boat-dog!