1967 Coupe De Ville convertible tri-toon project

Ive had an idea about turning an old school convertible into a boat for a while now. It all started when I had a 67 hardtop and needed to find a donor motor as my engine block was bad. A freinds dad had an abandoned convertible restoration project with a rebuilt motor. We made a deal and its been sitting behind my shop for 3 years now. Ive looked at several donor pontoon boats to start with and came across a steal I couldnt pass up yesterday. Its a 1987 20 ft pontoon basically striped down to nothing with an old johnson outboard and $1000 in new parts and carpet. I was actually looking for a trailer for my sun tracker and this thing fell into my lap. I paid the guy $900 and for it and im hoping ot sell off the parts and end up with some really cheap donor pontoons.


So basically what Im imagining is a 67 coupe de ville that sits right on the water (see little pontoon as possible), looks as close to stock as possible and at bare minimum can cruize around a no wake zone marina or booze cruize as my wife calls it. We live in discovery bay and she likes to idle around during sun down or just take the boat to a freinds house instead of a car. If you guys think its possible I would like to put a big enough motor to get this thing on plane and doing about 20-25 mph.

So here I am, big hopes and dreams. Stupid unrealistic idea? or could this work? Ive got a 10,000 square ft automotive fab shop, we build everything from drag cars to boneville cars, to street rods. Weve built a bunch of custom stuff like a turbo charged r1 powered rhino and a gsxr 1000 powered quad. Im definately not scared of the fab part, but I have zero back ground in boats. My shop is next door to the Ski Clinic where they manfacture their own freestyle trick ski hulls. So I do have some knowledgeable people in the area to turn to.

My easy budget minded plan was to transplant a 4 clyinder io set-up as it would keep the wieght down and get the job done idling around. Then when the plan got more elaborate and thoughts of venturing out into the delta entered the picture I started envisioning a tri-toon. Maybe section off the pontoons and have a valved system similar to a hydro hoist to take on water and lower the boat in a no wake zone and maybe pump out the water if I wanted to go out into the fast water areas.

thoughts? concerns?

heres what I have so far- wow i realized my pics arent very good- ill try and take some better ones.





here is a pic of my hardtop- basically i imagine the rocker right at the waterline. maybe even 4-6 inches up the rocker to cover half the wheel well.





weld up the door and fender gaps for one solid body. Leave the electric windows and convertible top so you could cruize closed up or top down. make the drivers seat seperate and do a wrap around L for 4 people total. what do you guys think?

 

cool, should be easy for you with everything you have at hand. i bet you will have the only 1 at the marina.

 

Lets see 2.25 tons of land yacht on 1.1 tons of floatation. Yep, should work out quite entertainingly. If it has a long enough snorkel, maybe you'd be able to see 25 MPH.

In all honesty, I don't know the size of your 'toons, but you'll never see anything but 6 MPH with the boat as you envision it. Simply put, calculate the volume of your 'toons in cubic feet and see where you stand. Whatever the total volume in water just one displaces, is the max you should load them up (50% volume). Full submerged, they'll perform quite poorly and then there's the stability issue. Ever try to ride a unicycle? This is how your car is going to feel up on a rig like that. It can be done, but you'll need to do a little math, lots of welding and probably some more math. It would be easier to just weld up a box under the car and hide an outboard in the trunk.

Why don't you just put a 502 with a 6-71 Jimmy in that puppy and have some fun.

 

This donor pontoon has 20 inch round by 20 ft long pontoons. The production weight of the car is 4500 lbs, subtract the frame, the all steel big block, Trans, rear end, wheels and tires, and. Virtually everything I don't need, I was hoping for a 3000 lb boat total. I understand it wont be built for speed or performance. Would a v hull be a better option for the stance or ride height I am looking for?

 

http://www.flickr.com/photos/innerspacealien/6842967444/

I think yours is more stylish.

 

i just threw up in my mouth- No this wont be an abortion project like that- I build high end street rods and wouldnt sacrafice a good convertible body without doing it justice. I am intersted to see what they used for a hull and drivetrain

 

I used to run a tuned/ported/piped /bored/stroked Honda CR500,but gave it up after breaking many of my bones

May I suggest a mind blower- how about an amphibian?
Not worrying about efficiency -make it a hybid gas/ electric with hub motors- no through hulls for drive shafts nor props.
Light as possible fiberglass.

I bet you could even get the Barrett Jackson crowd to pony up large for it,they pay too much for everything anyways.

http://www.youtube.com/watch?v=sgD-uhoucoU

 

that thing is sweet but way over my time and monetary budget- Id like to be into this thing for under 30K out of pocket

 

a car like that made a smooth ride by adding a lot of weight. the sprung weight to unsprung weight ratio is what it famous for ride comfort, back than it was done with brute froce: more weight. Not a good idea for a boat.

Better idea might be to find a or build a suitable boat hull, and just use body and trim parts (and seats?) off the Coupe de Grill to make it look like a Caddy. lots of cutting and welding but it will acheive a much better boat, and be a lot of fun to show off.

 

Pontiac Sunbird convertible - lobster boat:
http://www.boattest.com/resources/view_News.aspx?NewsID=3873
http://www.soundingsonline.com/news/coastwise/241122-its-a-car-its-a-boat-its-ca-boat
http://jalopnik.com/car-boats/
http://www.youtube.com/watch?v=Ioqv4yhsYZA
49 mph at the 2010 Pemaquid races: http://www.youtube.com/watch?v=6iT42FTsgYA
Another video: http://www.youtube.com/watch?v=9Lo5FgGT0zY

 

What ever hull you elect to use, it has to have the volume to support the weight, which includes you and crew, coolers full of beer and everything else. Assuming a 3,000 pound car, you must assume at least another 800 for 4 people, add a 100 for beer, plus several hundred more for full tanks, batteries, controls, pumps, engine, etc. The choice of hull shape will have little to do with your wish to go 20 MPH. It's just not going to happen with a car immersed to it's rockers, unless the below water portions are fairly well designed. Simply put, it'll take all the power the original big block could muster, just to get her up on plane, even with a jon boat style of hull under it. If the wheels were faked and just painted, on the sides of a jon boat style of hull and a tube frame to hold the Caddy sheet metal and interior, then you might have a shot. But dragging the wheel wells, wheels and some sort of immersed pontoon rig under it, just has way too much resistance to let her jump up on plane without several hundred HP at the prop.

This doesn't mean you can't putter around at 6 MPH (yep that's it, maybe 7 MPH with a tail wind), which would be fairly simple, assuming she's water tight. You'd make a wake like a garbage barge, but who cares, you're in a Caddy. Freeboard would be an issue, but if you drove it intelligently, in calm water, you'd be okay. Simply put, this has been done, just don't expect much in speed, without major thought and probably some professional help for the underwater portions.

Your 20' pontoons will support 2706.35 pounds at half submerged, which is where you want them. Sinking them further raises some safety issues (capsize). You could hide the pontoons under the car, with notches for the wheels, rockers, etc., so they don't look like they're there. Of course in doing this you reduce their internal volume and will need more anyway. This is why a jon boat style of hull is a batter way to go. You get more hull volume for it's length than 'toons. A jon boat style of hull will also offer, a much better chance of getting on plane too (faster then 12 MPH), because 'toons suck at this. Naturally, you'll need pretty big HP to shove this monolithic beast up onto plane, but it would be cool if you could. In the end, if you want to plane off (go faster then walking speed), you need a clean bottom and sides, so water can flow past without a lot of disturbance. To some degree you can force this issue, by adding power, but you have a weight penalty to over come, so this means even more power. A typical powerboat of that general size (estimated volume) will be half the weight of your CaddyLiner, so . . .

 

looks like some enterprising Cubans beat you to it. According to the web site I found these on these car/truck boats still had their drive train and tires etc. functional. the plan was to make it to US soil, ditch the floats/prow and drive to a relatives house in Florida.

 

what if he got 2 more pontoons , it would be pretty straight forward to put cross beams across 4 toons and mount the body to them.

 

nice accessorys

another boat car

 

Pontoons absolutely suck as if used to plane off. You just have to throw lots of HP at them to overcome their deficiencies.

The orange Dodge above shows a perfect example of what I was talking about. The top image clearly shows it's a boat with a car (actually I think it's a pickup) body draped around it. This works, because the boat does the wet stuff, while the car does the above water stuff. Also note the wheels are way tucked up in their wells, likely completely filled in from behind. The hull shape appears to be a Garvey or possably a cut up Bayliner (or whatever), so it's running surfaces are clean, neat and efficient. Assuming weight is kept manageable, this will work fine and look all of a car when just static at a dock.