I'd have to say that Chanel my 3 year old is a crazed water yorkie - Cheri is 11 months and isn't as happy in it as her big sister - but to get your yorkie used to the water..try playing with the hose - let them chase it without actually squirting and little by little the feel of water doesn't bother them ...
She has some water action shots in this link - but it's really not a normal yorkie pastime - She's just crazy !
WATER PICS LINK
A pontoon boat sounds dreamy ...what a nice life you must have to own one !!