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Hydraulic driven boat car

  1. Nov 13, 2014 #1
    So her is my predicament. I plan to convert my car to a amphibious car. Don't be negative and judgemental about it but I need help to figure out how I should power it on water.

    I have a 1400 lbs car. It has a 67hp engine. What I'm thinking I want to do is have a sprocket/gear attached to my crank shaft of my engine. In which I will have a hydraulic pump being chain driven from that spricket. In which two lines will be run back to where I want to take the impeller jet assembly off a jet ski. Where it will also be chain driven to adjust torque and rpm as need.

    I think that cover the jest of it. But what I need to know is how fast does jet ski assembly need to turn. What size hydraulic pump and motor will I need? Does my idea seem scientifically plausible the way I have thought of it?
  2. jcsd
  3. Nov 13, 2014 #2
    Ignore my crappy typo and grammar please. I'm a grease monkey with an idea. The rest of the calculations and stuff isn't my thing. I would do it through trial and error. But I don't have the funding...
  4. Nov 13, 2014 #3


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    Before you get into the mechanicals, how are you going to make your car float?

    Unlike the VW in this ad parody, cars are not known for being watertight:

    http://www.threesistersnovel.com/wp-content/uploads/2013/06/Tedkennedyvw1.jpg ​
  5. Nov 13, 2014 #4
    I have that part planned aready. It's acactually rather simple. Cars may not be water tight.. but in a relative way of looking at it. If you take off the roof. You have what would mildly resemble a boat. With tires. If you set that boat with tires in water. It will clearly sink. But is the water going to collapse it? Nope. It will come through holes in the floor. And the sides. And the corners. And miscellaneous locations. So its quite simply, a holy boat (;
  6. Nov 13, 2014 #5
    I just read under that picture (; rather interesting!
  7. Nov 14, 2014 #6
    The problem I see with the set up you propose is that the marine drive will be running all the time that the land drive is running, I think you need some kind of clutch in the marine drive.
  8. Nov 14, 2014 #7
    I figured I would be able to do something like on a actually compressor. With that but in clutch type deal. I just dont now how big of a pump I can run. And how big of a pump I will need. Or if what I'm thinking will even turn the marine drive portion fast enough.
  9. Nov 14, 2014 #8


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    And it will stay afloat how exactly?
  10. Nov 15, 2014 #9


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    Spoilsport! I was going to ease him into that by asking how he was going to keep his electrical system from shorting out... :p
  11. Nov 15, 2014 #10
    eurathan based plastic spray will be coated on the bottom 1/8 to 1/4 inch thick. Will be using the foam that is used in boats to stick top of that. And it will be shaved how seen fit. That no top of that will be fiberglass. Will have a sealed removable panel under the engine bay. Also the bump will be replaced with a square pontoon looking float. To hold engine weight. Better. For the cv axle they are gonna be tricky. Will sermon them when I get to it cause they move in every direction with bumps. I have a general idea but not for sure yet
  12. Nov 15, 2014 #11


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    Is it for fresh water only? If you use it in a marine environment, how will you remove the chloride ions from any exposed steel, (such as the suspension), after it has been baptised?
  13. Nov 15, 2014 #12
    I live in northern minnesota. Whats salt water?
  14. Nov 15, 2014 #13


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    So, now you mention sealing. Before, you said that it would leak through multiple locations and would indeed be a "holy boat".
    One thing still puzzles me immensely: what the hell kind of car has a 67hp engine?! That's barely more than a decent chainsaw.
    Anyhow, I'd recommend going with a belt drive rather than chains, simply because you don't need precision, it would be a lot quieter, and you wouldn't have to worry about lubrication or corrosion issues like you would with metal.
    Also, depending upon local laws, you might need to obtain a boating license in order to legally put it in the water.
  15. Nov 16, 2014 #14
    Hydraulics are heavy and inefficient. Assuming you want to transfer a fair amount of the 67 hp and you are using utility type equipment your hydraulic system will most likely be well over 200 lbs. For this same weight and about the same cost you could have a second motor directly connected to the jet pump. Another choice would be to use an electric system from a hybrid car but this will be only a little lighter and more expensive. A drive shaft may be a better choice if possible.

    Most of the 6" jet ski pumps were originally designed for about 50 to 60 hp. Of course as time went on they kept increasing the power and pitch and area on the impeller. For about 60 hp a 6" jet pump should turn about 5000 rpm. More pitch and area on the impeller will make for a lower rpm at this same power.
  16. Nov 16, 2014 #15


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    Yes, you;re gonig to have a heckuva time balancing weight.

    And keeping it from rolling. It may actually be too buoyant to be stable, and may go turtle on you.

    Look how low in the water this amphicar needs to be so it doesn't flip.

    BTW, how will you seal big seams like the doors. Lot of pressure there. These amphicars leak like a sieve.

  17. Nov 16, 2014 #16

    jack action

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    To size the pump and motor, you first need to know how much power you need to do what you want. Interesting links:
    For the speed of a jet ski assembly, this motor with jet drive develops its 80 hp at 5500 rpm and it's a direct drive. There is also a «conversion guide» that seems to suggest you need less power with a jet pump than with a prop shaft. I suppose it is because there are no transmission losses since it is direct drive.

    [/PLAIN] [Broken]
    Last edited by a moderator: May 7, 2017
  18. Nov 16, 2014 #17
    I work on ch-47 chinooks for the army. Which is 90% hydraulics. And you are the first person I have ever heard say hydraulics are heavy and inefficient. Could you explain your reasoning behind that? Also that you very much a had no clue what rpm the jet pump would need to spin.
    Hybrid is out of the picture because I don't feel save with all that electricity... on a water source lol. And I thought about the 2nd engine but I'm doing this work on a 1993 ford festiva. And I want to be able to have 4 seats.
  19. Nov 16, 2014 #18
    I thought about belt drive but belts slip? And that would be loss of power? Yes I will neneed a boat license on it which is 37 dollars. A 1993 ford festiva wI'll be my car of choice
  20. Nov 16, 2014 #19
    I figured I would conquer weight and balancing when it arose. I was thing extendable arms on each side with floats on them like some sail boats I believe it is has. And for doors.... ohh doors. If necessary I will weld the majority of the door shut and make it custom. If i can, what I want to do is look aat the 1990s cj3 jeeps. Which have sealed cabs. I wold borrow some ideas. Also I was thinking. A dam good seal on the door and then a lever that will suck the door in tight against the jam.
  21. Nov 16, 2014 #20
    So do you by chance have a general idea of what I would need and where I could locate such materials. 70hp engine (1395cc) and it will be a jet ski assembly so it will be at 5000-5500 rpm. And I will not be attaining jet ski speeds at all. I would be happy with 15 to 20 mph. Pushing it. Don't Wana risk flipping too much.
    Last edited by a moderator: May 7, 2017
  22. Nov 17, 2014 #21
    First commercial hydraulic motors are very different from aerospace. Weight and duty factor being the most important differences. Second most hydraulic systems in aircraft are very low power on the order of a couple of horsepower. Power transferred is what requires the weight much more so than force transferred or amplified. Third, more modern aircraft are going to electric or electric over hydraulic to save weight. The C-47 is a very old design and at that time they did not have light weight electric motors like are very common today.

    A typical industrial hydraulic pump of the size you need is about 80 lbs. You need two of them so are up to 160 lbs. Then you need hose, fluid, tank, cooler, etc. You will be well over 200 lbs and maybe over 300 lbs.

    What do you mean I have "very much no clue" as to the RPM that the jet pump needs to spin? My 60 hp driving a 6" pump spinning about 5000 rpm is not only near what you say in a later post but also typical real life for a jet ski pump like you proposed to use. Keep in mind that a jet pump is not a prop and the RPM is mainly a function of the power and the pump and not the speed of the boat.

    Have you ever seen the hull speed equation: https://en.wikipedia.org/wiki/Hull_speed Since your desired speed is well above hull speed you will be planing. To do this requires a fairly good hull design and a fair amount of power. Getting on plane will take a minimum of about 30 hp for a vehicle of the weight you propose if it has a fairly good hull design. The amphicar was much slower at about 4 to 5 knots so was displacement.

    There are cogged belts that do not slip that can easily handle 80 hp. Check out Gates. The claimed power loss is only a couple of percent. A hydraulic system would lose about 25% or more. An electric system would lose about 10%. Also keep in mind that a gas engine and even a Diesel engine has an electrical system including a starter. Electrical systems have been used for years in boats. Many large boats/small ships actually have serial hybrid drive systems.
  23. Nov 17, 2014 #22

    jack action

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    From the very simple equation you can find on one of the link:
    You need 1400 / 25 = 56 hp. That is for known hull designs. I'm guessing your «hull» design (with the wheels and all) will create more resistance than the one from a typical boat; So higher power demand will probably be in order (or your speed greatly reduced, since this is about the total power of your engine).

    That means you need a pump able to handle at least 56 hp.

    You need a motor able to handle at least 56 hp.

    You need a jet pump sized for a motor that produces around 56 hp (I guess a 70 hp assembly should work since you will probably use the entire power of your engine).

    The rpm of the pump must match the rpm of the engine (otherwise a gear ratio will be needed to match the two together).

    The pressure output and flow rate of the pump must match the ones for the motor.

    The rpm of the motor must match the rpm of the jet pump (otherwise a gear ratio will be needed to match the two together).

    I'm gonna leave the shopping part of your project to you.

    Putting all of this together should work. But this is a very simple analysis for a backyard project. Results may differ unexpectedly.
  24. Nov 17, 2014 #23
    Hahah I'm so sorry. What it was supposed to say was. THANK YOU very much as I had no clue what rpm would be required. I gotta start proof reading!
  25. Nov 17, 2014 #24
    Okay. Now I am becoming intrigued to your electric idea. My fear of it is. Don't I need one of those big 4000 dollar hybrid batteries if I was to use a electric engine big enough to move the car? And that the only fear I have is because those are deadly. I'm by no means an electrician. And idk how it would go if I was sitting by one and it sunk..
  26. Nov 17, 2014 #25
    You do not need a battery at all. The gasoline motor connects to a generator. Wires from the generator connect to an electric motor that is then connected to the jet pump. The generator and electric motor will each need a controller. If you have no electrical experience this may be more complication than it is worth. Maybe the most simple method is the second motor for water propulsion.
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