Don't use polarized sunglasses in an airplane for the aforementioned reasons. For sure, don't use them in a seaplane.
The best bet I've found for near vision is the stick on bifocals available in a lot of places. Take your regular sunglasses, put a drop of water on the little stick on bifocals, and place the bifocal where you want them. Move em up or down, cut them in half if they are too big, make a set of TRI focals if you want, by combining two sets of stick ons.
They are available in lots of places. Here's a link:
http://www.goodglasses.com/index.cfm/fa ... DQod2T-7JwI've used these for years, they work great and are CHEAP.
MTV