Amphibious Atlantic Cruiser

Hello! I have literally no idea what I am doing, hence my name.

I have never built a boat. I have never worked with fiberglass, or carbon. I don't know how to calculate an object's buoyancy, and no, I have never actually worked a sailboat, though I have been on them while they're out on the water.

That said, I have long been inspired by Ben Carlin and the story of the Half-safe. For those who haven't heard that one, Ben Carlin is an absolute mad man, who circumnavigated the globe in an amphibious jeep. So far the ONLY person to circle the globe in an amphibious vehicle.

I doubt I'll ever be able to do this myself, but that doesn't stop me from theoretical boat building, and I have several sketched out designs. The problem is, I am An_Idiot, and I have no idea what I'm doing. I'm not sure what hull shape or material would be best, though I have some ideas. My biggest worry is stability in the water. In order to be legally driven on U.S. roads, it has to meet certain dimensions. It can be a maximum of 45ft long, 13.5ft tall, and only 8.5ft wide. (13.5m long, 4m tall, 2.5m wide if we are using metric.) Sideways stability seems like it'd be a real problem on a boat like that.

I was wondering if I could get any thoughts or suggestions from people who know a boat actually works, and maybe ask if someone could show me how to calculate my waterline?

 

Welcome to the Forum Mr Smart (not idiot) - you are smart because you decided to come on here and seek some advice before you start to chuck truck loads of $$'s at your project.

Google came up with these interesting links about Ben Carlin -
Ben Carlin and the World's only circumnavigation by amphibious vehicle • MotorPunk https://www.motorpunk.co.uk/articles/ben-carlin-worlds-circumnavigation-amphibious-vehicle/

Ben Carlin - Wikipedia https://en.wikipedia.org/wiki/Ben_Carlin



Could you maybe take some photos of (or scan) the sketches that you have produced so far, and post them on here?

 

Yeah I can do that.

The first one was intended to be kind of a catamaran design, but I ran into the problem of the drive axles needing to be enclosed, so it ended up as some kind of trimaran? Each square is intended to be 2ft², and I'm leaving 4ft at the bottom of the vehicle solely intended for internal systems. Fuel and water tanks, battery banks, engines (which may require more room?), Etc.

The second one is so far my favorite. Not exactly a deep V, but should provide some space for storage and displacement, but again, I have no idea how to calculate that.

Last is a little set of sketches I did looking for a more exact approximation. The scale changes to 1ft², but I also did it in pen while I was at work, so these are really rough, even compared to the first two. I'm not considering rudders or props yet, I think the first thing I need to do is settle on a hull shape. I'm also considering a deep V hull shape with a drop down keel, but I don't know how big those are, and I think the drivetrain would be in the way, unless there were two drop downs, one on either side.

Edit: Wait! I could put a drop down keel at the far back, after the drivetrain ends! I didn't even think of that til I was looking at those sketches.

 

For your inspiration the smartest amphibious vehicle I know. It's probably not the most efficient though and the presenter mixes up some terminology.

 

That M3 video DID give me several ideas. I had thought of expanding the deck with a couple inflatable pontoons and folding platforms, but I would be worried about blowing out the floats.

I actually really like the idea of waterjet propulsion. A high cruising speed would be ideal for crossing the Atlantic. I was thinking about having either a collapsible sail, or an electric fallback system, in case I run out of fuel while in the middle of the ocean.

I had thought of expanding the deck with folding platforms and/or inflatable pontoons, but I would be worried about structural integrity of folding platforms. I don't really have a good argument against inflatables, but I am iffy about them.

 

Slow down old chap, and re-assess what your priorities are here.
If you really want to cross the Atlantic, then build a yacht suitable for this task. Or (even easier and much cheaper in the long run), buy a second hand yacht in good condition that is well equipped, so that you could set off next week.

They talk about high speed in the video that Floatation linked to, but those bridge units can only spin around in circles fairly quickly - I would not say that they are 'high speed' when going from A to B.
If you want to cross the Atlantic under power, then you ideally need a much more efficient hull form than an amphibious vehicle. I am impressed that Ben Carlin's jeep managed to cross the North Atlantic under power, and that he had the fuel capacity (I presume petrol?) to do it. In the motorpunk article in my previous post they note that he had 220 gallons of fuel, and that with this they were able to motor 1,700 miles from Nova Scotia to the Azores - that is almost 8 miles to a gallon, which sounds rather optimistic to me.

Here is another video about his craft - in it they mention that he was now able to carry 800 gallons of fuel - maybe he did have 800 gallons of petrol on that North Atlantic leg?

 

The biggest problem I see with your idea is size.
To motor across an ocean in a small boat requires two things:
1.) a very small engine, and
2.) a very large fuel tank.
IIRC, Half-Safe towed a submerged fuel tank behind her.

With a displacement powerboat, the slower you go, the greater your range. And when I talk about speed, I'm talkin Speed/Length ratio (S/L). This is the square root of your waterline, in feet, in knots. So, if your waterline is say 20 ft long, an S/L of 1.0 is 4.47 knots, or about 5.14 mph. But to get this, you need about 1.0 hp per ton of vessel weight.
If you had a really efficient small diesel, you may be able to get maybe 20 horsepower hours per gallon (hp/gal). This could give you a theoretical range of maybe 89.2 miles per gallon, if your total weight is 1.0 ton, but you would need a very hydrodynamically cleen boat to do this well. Plus you would need a very small engine. Bigger engines use more fuel at slower speeds than smaller ones. The wheels hanging out there create a lot of drag. Also, your boat is likely to weigh much more than a ton, especially with all that fuel aboard. So, with a much heavier vessel, plus the drag of the wheels, you might get 20 mpg at that speed. And this is probably a stretch.

But even at 20 mpg, to get across 1,000 miles of ocean, you're going to need at least 50 gallons. And this is throgh flat water with no wind resistence and no unfavorable currents. To deal with those, you're going to need more hp and much more fuel.

Suppose you end up against a 2.0 knot current. This will have to be subtracted from your 4.47 knot speed. Then you will be traveling at only 2.47 knots (2.84 mph). But your fuel consumption is measured by the hour, not by the mile. So now you're getting only 12.7 mpg.

This is one of the reasons Steam ships got so huge. The bigger the ship, the longer the waterline. And the greater the capacity to carry cargo and fuel. The s/l speed goes up with the length.
For instance, a ship with a 100 ft waterline would have an s/l 1.0 of 10 knots. Assuming its engine had the same effiencey, and it weighed 1,000 tons, it would burn about 1,000 gallons per hour. But it would travel 1o nautical miles (11.5 miles) per hour, not 4.47 nautical miles (5.14 miles). Now, when you divide the hp by the weight, 1,000 tons/ 1,000 hp, you end up with the same hp per ton. But the bigger vessel is going more than twice as far for the same rate of fuel usage ( 1.0 gal per ton). And if it encounters the same 2.0 knot contrary current, it will be slowed down to 8.0 knots, or 9.2 mph.

I hope this gives you some idea of what you'd be up against.

 

I'm out of my depth here.

But - I wonder how much luck would be involved taking a vessel that thin around the world. Unless, you made it self-righting. Or perhaps if it was a folding trimaran - thought it could still flip.

Depending on weather, it isn't completely implausible you might run into an occasional 30 or even 40' storm waves. (E.g., NDBC - Science Education - How are ocean waves described? https://www.ndbc.noaa.gov/educate/waves.shtml) If you are talking a long voyage, the chances of running into big waves goes up.

I'm not clear why you want an amphibious vehicle for your journey. Maybe there is a good reason why the overwhelming majority of trans-oceanic vessels aren't amphibious.

I'm reminded of the story of Oskar Speck, a German who took kayaks on a trans-oceanic journey in the 1930s. By the end, WWII had begun, and he was imprisoned as an enemy alien in Australian internment camps for 6 years. I think they were folding kayaks, so he could possibly have backpacked part of the journey on land - would that count as "amphibious"? Or maybe you could take a folding bike. Problem is, to literally go around the world by any route that involves land, you pretty much have to travel through countries that are unfriendly towards each other. If you instead pass through canals, the Middle East has always been a powder keg of nations ready to go to war with each other. By the end of your journey, the U.S. and China might be at war too. The conflict between the U.S. and Russia might be more direct. And the Middle Eastern powder keg could be blowing up. Are you sure this is a good time to do what you dream of?

And if you instead go south of the Africa, you might again hit 30' or higher waves.

BTW, in many countries, there are a whole bunch of laws and regulations, and I think testing, that street legal vehicles have to meet. There are expensive experts who specialize in meeting those laws. It may be a bit easier for experimental vehicles. But still, if you want to start from scratch, you are asking a lot of yourself. Is it possible it would be easiest to start with an existing vessel, and strap on extra fuel tanks?

BTW, some "folding trimarans" can be trailered. Possibly the extended pontoons would give it a bit more stability in big waves. If you could carry the trailer on top of the boat, would that count as a amphibious vehicle in your book? I'm not sure, BTW, if any are suitable.

It is possibly easier and cheaper to fly commercially around the world. Isn't that enough of an adventure? You could see many countries along the way, using rented cars and boats, and/or using trains, and you could perhaps avoid potential warring countries.

 

@mitchgrunes I guess it takes all types of people to make the world go around - and some folk will insist on doing things the hard and difficult way (actually, even a comfortable sailing yacht falls into this category occasionally) rather than a safer, easier and cheaper way (like flying commercially around the world as you suggested).

Re a trip across the North Atlantic, an amphibious jeep would be positively palatial and luxurious in comparison to the mighty 'Big C', whose owner intends to cross the North Atlantic next summer from Newfoundland to Ireland.
He will be singlehanded - there is no room for anybody else on board, literally!

 

You HAVE to see these, before any major decisions

 

Watercar.com is interesting, albeit high powered sports amphibians rather than ocean crossing.

 

Electric hub motors might make the mechanics of retractable wheels and drives simpler.

 

I'd like about a 30ft dagger board mono or even a Cat or Tri with minimalist amphibian capability. Just enough to crawl out under its own power up a boat ramp and travel on paved roads up to 10mph for 5 miles. The wheels could double as boat fenders and life preservers. Probably toothed belt or chain drive and if it takes a manual operation besides pushing a button to rig the belts or chains on the road wheels after the "landing gear" is locked in landing config that would be OK. Just so a fairly large boat can get to a parking lot near by the marina. Not too worried about "road legal". I've done lots of odd-ball operations on roads related to construction and never had a bad experience with local cops. Just be sober and respectably dressed and behaved, and do any moves on major streets at 3:30am and have lots of lights and orange flags all over it and pilot car and no worries.

 

Like the late Derek Kelsall design


http://www.kelsall.com/News/KCNewsAug13.pdf

 

I guess that's one way of doing it and would be nice and shallow draft with wheels down and wheels act as fenders.

They got these, and some dinghies and IIRC Bic kayaks have tiny wheels embedded in the stern of the keel. I thought it might be nifty to have another wheel embedded near the bow so you could ram a typical boat ramp without gouging the bow, then you flop over sorta on one side and that would be "the brakes", then after you climb out you can roll the boat up sorta like walking a bike on its two wheels. Could use oars or disconnected double end paddle to be an extension handle so you could walk the boat on two wheels without being bend over.