This is something I think a lot about when I’m bored. It’s an interesting engineering challenge, and I like the idea of terrifying my passengers by driving full-speed into a lake, so I’ve been designing amphibious cars in my head for a while now. My current plan involves a conventional ladder frame chassis to support the drivetrain, and a wooden inner support structure wrapped in a one-piece fiberglass body (with the exception of the hood and trunk lid, of course). The drivetrain would be a longitudinally-mounted Datsun A-series engine, because they’re lightweight, reliable, and make/can be made to make enough power to get the thing to keep up with traffic. this engine would send power through either a manual or automatic transmission to a small transfer case (from a Samurai, perhaps?), which would then send power back to the front wheels, while the other end of the transfer case would send power to a propeller in the back (I figure the car should be front wheel drive because that will assist the car in climbing out of the water). I’m thinking of mounting the radiator in the back so that I don’t need to put a functional grille in the front (though I might put some Karmann Ghia-esque fake grilles up front for style). Less water should get in the car that way. It won’t have doors, because doors leak too much. Screw ‘em. Instead, it should have molded steps (perhaps chromed?) in the sides to help you step over the edge and into the car. I also don’t think it should have a roof, because that’s added weight, complexity, and work in a vehicle that you wouldn’t want to use when it’s raining anyways. Brakes should be inboard to keep them out of the water, and it should have three headlights. No particular reason why, I just want three headlights. I call my fictional amphibious car design the Otter, because otters are cute and amphibious, so the name fits.
So how would you design an amphibious car?