How would you build an amphibious car?

"Jim Spanfeller" (awesomeaustinv) 03/24/2020 at 18:59 • Filed to: None

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BEHOLD MY TERRIBLE HANDWRITING.

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?

CarsofFortLangley - Oppo Forever > Jim Spanfeller 03/24/2020 at 19:02

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Canoe with wheels

Jim Spanfeller > CarsofFortLangley - Oppo Forever 03/24/2020 at 19:07

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Nice. I’d add a lawnmower engine to it, though.

415s30 W123TSXWaggoIIIIIIo ( •_•))°) > Jim Spanfeller 03/24/2020 at 19:11

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Aremmes > Jim Spanfeller 03/24/2020 at 19:14

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Step 1: Buy a DUKW.

Step 2: ????

Step 3: PROFIT!

Highlander-Datsuns are Forever > Jim Spanfeller 03/24/2020 at 19:14

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Carb and exhaust are on the same side on a Datsun motor. Minor technicality for an otherwise flawless execution.

gmporschenut also a fan of hondas > Jim Spanfeller 03/24/2020 at 19:17

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I’m thinking ATV with side pontoons with mini outboard. 

Future next gen S2000 owner > Jim Spanfeller 03/24/2020 at 19:26

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Turbine, mounted externally on the roll cage. Fully isolate the cabin from the wheels/brakes/suspension through digital everything. No prop or trans to deal with and a water tight h ull . Air , long travel suspension to  bring the wheels up.

Boom.

winterlegacy, here 'till the end > Jim Spanfeller 03/24/2020 at 19:28

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I’d probably go midship engine with the front having some sort of ballast adjustment. Then again... y’know how sports cars have REALLY long noses sometimes? Shove an inline 6 up front and somehow figure out how to turn it into a car speedboat.

Daily Drives a Dragon - One Last Lap > Jim Spanfeller 03/24/2020 at 19:36

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For waterproofing reasons, i think I'd personally go with a chain drive on the rear end like an pre-war truck. 

Just Jeepin' > Jim Spanfeller 03/24/2020 at 20:10

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Someone on FP pointed out that Brooks Stevens, one of my Jeep heroes,  designed this amphibious car. Pretty cool design.

!!! UNKNOWN CONTENT TYPE !!!

Just Jeepin' > Jim Spanfeller 03/24/2020 at 20:12

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Also, I’d never heard of the Weasel until just now.

https://en.wikipedia.org/wiki/M29_Weasel

CRider > Daily Drives a Dragon - One Last Lap 03/24/2020 at 20:22

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Chains are prone to rust and stretching , though.

CRider > Jim Spanfeller 03/24/2020 at 20:33

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Carbon fiber tub for a light, waterproof passenger compartment. Sevan Ma rine has a 557 Series outboard motor based on the LSA V8 from the second gen CTS-V , so that would be a good place to go for a waterproofed powertrain that’s powerful and reliable. I'd also figure out a way to make the active aero convert into a hydrofoil in the water for extra speed. 

wkiernan > Jim Spanfeller 03/24/2020 at 20:38

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Duct tape some large styrofoam blocks on the sides of my Miata, bolt a couple of oarlocks on the doors, I’m good to go!

Nom De Plume > Jim Spanfeller 03/24/2020 at 20:53

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Underwater, duh.

Snuze: Needs another Swede > Jim Spanfeller 03/24/2020 at 20:55

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Id talk to the naval architects I work with!

One thing to consider, front engine puts a lot of weight on the bow which will make it really hard to get up on plane, assuming you’re designing a planing hull. And planing hulls are ideal because they are stable and efficient.

If you could put that drivetrain in the back but otherwise run it as you describe I think you’d be in business.

What I’d consider is a series hybrid with no battery. Basically a gas engine with a clutched generator so I could run the screw or run the generator, and a pair of drive motors driving the front wheels. Something on the order of 50-75 HP each. This gives some advantages because you can run it all AC which means smaller generator/motors and it greatly simplifies the electronics and you don't need costly inverters. 

BaconSandwich is tasty. > Aremmes 03/24/2020 at 21:17

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Step 4: sink?

BaconSandwich is tasty. > Jim Spanfeller 03/24/2020 at 21:26

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How would I do it? Hmm, good question. I’d probably do the following:

- electric drive train, possibly with a small three cylinder as a backup, running as a series hybrid

- try to disguise it, but curl the front so that water travels under the vehicle. It’s got to have a way to either go under or around, and under sounds more efficient.

- a large running board on both sides , to provide a place to step in/out of the vehicle while in the water. Running boards could also act as floats for added floatation.

- sunroof for ease of egress, if it comes to it.

Aremmes > BaconSandwich is tasty. 03/24/2020 at 21:51

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Step 3.5: Avoid storms and barges.

A Boy and His Longtail > Jim Spanfeller 03/24/2020 at 22:49

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This bad boy is already running around my town

Jim Spanfeller > Daily Drives a Dragon - One Last Lap 03/24/2020 at 23:55

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That’s probably a smart move. Perhaps rear braking could be accomplished with a brake on the driveshaft, like in old Model Ts.

Jim Spanfeller > Snuze: Needs another Swede 03/25/2020 at 00:02

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Hmm. I’ll be honest, I don’t really know much about boat design or hydrodynamics other than just make sure it’s sealed so it doesn’t sink. I was thinking at the very least, I should probably make my design front mid-engined. for slightly better balance. I wonder if I could move the transmission and transfer case to the back to even things out even more... 

Jim Spanfeller > BaconSandwich is tasty. 03/25/2020 at 00:04

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Electric would definitely help solve the cooling problem and keep it well-balanced. The challenge of course would be keeping water away from the electronics...

Jim Spanfeller > winterlegacy, here 'till the end 03/25/2020 at 00:08

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I think my plan would be to give it a long nose, but keep the little Datsun engine and place it well behind the front wheels, for a front mid-engine layout. Perhaps shift the transmission and transfer case rearward as well to further even out the weight distribution...

Jim Spanfeller > Future next gen S2000 owner 03/25/2020 at 00:12

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So... like this

plus this

plus this?

Sounds like a plan to me!

Jim Spanfeller > A Boy and His Longtail 03/25/2020 at 00:13

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Does it float though? I suspect it doesn’t, but I really want it to.

Daily Drives a Dragon - One Last Lap > Jim Spanfeller 03/25/2020 at 00:29

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Yeah. This is taking your inboard brake setup to the next level. That might be not so good for weight balance reasons though. I didn’t really put too much thought into this idea. 

Daily Drives a Dragon - One Last Lap > CRider 03/25/2020 at 00:30

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You’re right. However, they’re not the worst thing to replace so.... Idk. It’s an amphibious car. It’s not supposed to be all that practical. 

A Boy and His Longtail > Jim Spanfeller 03/25/2020 at 00:47

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I don’t think so either, but I like to pretend I’m riding around on it and just decide to take it from the load to the water.

Jim Spanfeller > Daily Drives a Dragon - One Last Lap 03/25/2020 at 00:48

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I think it could work. Might have to rearrange the drivetrain a bit for better weight distribution, but it could be a decent solution to the problem of rear drive and brakes.

phenotyp > Jim Spanfeller 03/25/2020 at 01:05

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I’ll see if I can get some pics of Christian Felske’s Schwimmwagen model from Pforzheim tomorrow. I have a bunch of scans in a binder from 2001. He took the idea of the VW Schwimmwagen

and crossed it with a jet ski, back in the 90s.

Snuze: Needs another Swede > Jim Spanfeller 03/25/2020 at 07:09

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There are a lot of kinds of boat hulls out there and they are all trade-offs. The “seal it up and hope it doesn’t sink” approach is a “displacement hull.” And that is one thing to backup and consider, things don’t float just because they are sealed, theu float because they displace a greater mass of water than they have mass. In other words the overall d ensity of your craft (including air volumes and such) has to be less than the density of water.

Going back to a displacement hull, think of a big, rectangular barge. There is no hydrodynamic optimization, it just meets the most basic premise of displacement. They float, they are very stable in calm water, but are awful in rough water and require gobs of power to push.

Next would be a more optimized hull like a canoe, sailboat, or cargo ship. Its still basically a displacement hull, but its got a sharp prow at the front, narrow rear, rounded bottom, and strakes for stability. It still rides low in the water but its much more efficient than a barge hull.

Then you have semi-planing and planing hulls. These are most types of power boats. They are similar to a n optimized hull, but with a sloping hull underneath. As they increase speed they generate lift to ride up out of the water such that only a small portion of the aft end and propulsion system are still in the water. It greatly reduces drag and has good directional stability, especially on plane, but trades off low speed, non planing maneuverability.

The problem with amphibious cars is there are a lot of trade offs between what make a good car and what make a good boat. For example a planing hull is not the best use of space to get a practical car shape. But weight in the back is key to allow planing and having any kind of speed in the water. 

Future next gen S2000 owner > Jim Spanfeller 03/25/2020 at 14:37

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I mean, you aren’t too far off. You’ve got the general idea.

phenotyp > Jim Spanfeller 03/26/2020 at 18:22

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I found those pages of Felske’s Schwimmwagen!

The idea is that the driver sits in back, jet-ski-style. The rear wheels rotate 90 to be the props when in the water, as shown in the photo of the model:

What the dude on the right is doing... I have no idea.

Felske went on to be a head designer at VW, first in Barcelona at DCE, then VWCA. No idea where he is now, but I’m sure that he was last sketching around 2004. Now I’m sure he wears a suit and runs meetings, unless he’s retired to the spanish coast by now.

Dude could fuckin draw . He was kinda the poster child at the studio I first interned at, in 2001. I have tons of other copies of his school/internship sketches.

Jim Spanfeller > phenotyp 03/27/2020 at 00:14

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Whoa.

phenotyp > Jim Spanfeller 03/27/2020 at 00:29

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Yep.