Hovercrafts

Swim as in float? If so then yes

Please dont try to build one could be dangerous

Not as far as I know, the skirt which keeps it afloat relies on the engine to keep it inflated, cut the engine and the skirt will deflate. Though I wouldn't be surprised if there's a buoyancy aid on at least some hovercrafts to help it stay afloat.

They are beast... Found myself a bit too close. You can't see it in the vid, but i had to move back xD that thing was gigantic

I think they swim freestyle, but I could be wrong