We have used one (largest size, Baltic, I think) and he (Jake, a 6 stone Hovawart) doesn't seem to mind it after a while and appears comfortable sitting/lying down but he's never fallen in so I don't know how long it would keep him afloat once he was tired from swimming or if I could lift him anyway - whatever, we prefer him having it on to not as at least it gives us something to grab him by rather than his collar if he fell in and would give us time to work out a way of getting him back on board (small crane I should think!).
New long-haired Weimaraner puppy will be getting hers on when she's big enough to board the boat by herself as well.
I spoke to someone (Deleted User?) at our MBC dinner last week about these and the consensus was that they probably didn't have enough buoyancy in them but would buy you some time so you could rescue the dog.
actually, i'm not alowed to use a search engine but what the hell. You may find that the dog is a bit too fat, so put him on a diet, it's good for them. I had a dog that I trained to eat less and less food, and eventually he was much thinner. But just as I had trained him to eat nothing at all, he unfortunately died.
MBM tested most of the then available pet buoyancy aids in the Aug 2000 issue (p34). Details in the index section of www.mbmclub.com or from the Indexes button on the bottom nav bar, including details of the Copyshop service.
my dog's able to be on board for several hours without needing to go provided we take him for a walk 'n wee first! after that if he got desperate we'd let him go in the cockpit and hose it off - no trees on boards but perhaps if I hold the boathook vertically he'd think it was one! Lucky I don't have a wooden leg!!