In and out of water : Terra Wind
For those that cannot decide between a motorhome and a boat, this is the solution although it does come with a USD850k price tag. It is the Terra Wind, it manages seven knots in water and is manufactured by Cool Amphibious Manufacturers International of Ridgeland, S.C., USA. Ten years after its invention, sales have not been very good - at all!
From the outside it looks like a motorhome but underneath it is more like a DUKW which makes up a significant chunk of its 14 tonne weight.
As might be expected it is designed only for use on very quiet lakes, nothing too difficult. Even the the pontoons on both sides won't help much in a storm!