sea-worthy amphibious craft?

Discussion in 'Boat Design' started by jkittel, Sep 26, 2007.

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  1. kach22i
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    kach22i Architect

    The US Navy put 13.6 million into a robotic Jet-Ski (a single prototype)...............but I'm just a stupid taxpayer.
     
  2. Jongscx
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    Jongscx Junior Member

    My first question was whether it was to be primarily a land vehicle or a boat. But you answered that already.

    My suggestion would be a multi-hull, possibly a cat and have wheels fold into the middle. Now, did you want them to retract automatically, or are you fine with having to bolt them on/off each time?

    Another idea might be a trimaran with the outriggers folding up. Then the wheels would extend down from there. You could then build a larger boat, because you would have the stability, but still stay at your 16ft width on land.
     
  3. jkittel
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    jkittel Junior Member

    Yes, I think Trimarin with folding outriggers is probably the best solution. Even if wheels are used instead of tread, large wheels are not cheap, and keeping them dry and protected during long voyages would be a big priority. I like the idea of folding outriggers because they could still be deployed on land, allowing the boat to generate electricity from a wind turbine both at sea and on land, albiet stationary.

    Depending on how the outriggers are attached, they could be used as very slow moving oars to pull/lift/drag the boat at a mild 1mph. Something like the backswimmer beatle when its trapped on land...
     
  4. Jongscx
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    Jongscx Junior Member

    Could you just use a bunch of small wheels? Although cost-wise, it may be the same...

    moving them about would be more manageable, and getting individual units damaged wouldn't be so costly.

    I was thinking about the old russian tanks that could have rubber wheels installed in place of the tread/runners... If you had to beach somewhere that had soft ground, you might be able to get some type or rubber tread to temporarily increase your footprint...

    Not sure, it's late and I'm tired... but it sounds good while I'm typing it...:p
     
  5. rwatson
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    rwatson Senior Member

    Another concept

    Just to throw some ideas in the pot - I favoured a tracked version till I found out how expensive and delicate they were.
    The speed thing on land is not important to me, but at sea a decent speed would be usefull.
    The idea of solid tyres is along the right line I think - getting a flat tyre on a pneumatic tyre could be tricky, and they get bogged on sand easily.
    I envisage one wheel on each side, an aluminium version of the old solid tractor wheels, the ones found on early non rubber tyred tractors. A solid metal rim (maybe with a layer of solid rubber around it), about 2 ft high and 3 ft wide for the boat.
    They had ridges across the wheels to help with grip, and were wide enough to spread the weight across a large ground area.
    Fitting this to a conventional hull is a design problem, but I have been looking at a Bolger design in boats called a step sharpie.
    http://www.ace.net.au/schooner/fms.htm
    It has a flat bottom with a step in it. These boats can get 30 mph with 100hp outboards, so that is great. The flat bottoms could allow the solid tyres to act as paddlewheels during the transition from water to land and vice versa. The flat bottom section makes it easy to have the wheels raise and lower as required.
    I have attached a rough concept to illustrate the idea.
    Could this work I wonder ?
     

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  6. Jongscx
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    Jongscx Junior Member

    Would it be better to have the wheels in the front? as they would be in contact with the ground sooner... then, it would skid on the hull for a while, until the rear wheels contacted the ground. Wear wouldn't be too much of an issue as this would only apply when you're having to climb a sandy beach (or i'm totally wrong on this one...)

    I don't see the advantage of having a large metal wheel though, except for simplicity...
     
  7. rwatson
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    rwatson Senior Member

    Yes, there are some good points in what you say.
    My thinking is as follows.
    1) Only 2 main driving wheels, and the small retractable steering wheels at the bow for sheer engineeering simplicity. For a start, no need for suspension as a tricycle always has its feet on the ground ( similar to the other smaller amphibious boats sold by Sealegs in new Zealand)
    2) Wheels at the rear, for the same reason tractors do - that going up hill, the weight provides traction to the load bearing wheels. Front wheel drive can lose traction.
    3) Big wheels in diameter and width to handle sand, rocks and generally rough surfaces with about 2 tonne of boat.
    4) The ability to 'paddle wheel' when coming ashore - when its too shallow and dangerous to leave the outboard leg down any more.
    5) Simple agricultural engineering = low cost and maintenance

    Lots of smaller wheels need individual suspension, lots of bearings to get salt in, go rusty or oxidise. Tall wheels keep their bearings out of the sand and constant immersion in salt water. There is also the problems of 'putting the wheels away" when motoring or sailing at sea - if they were left in place, they would create lots of drag. In the case of 'lots of wheels', we have the problems of supplying drive to numerous wheels - electrics and hydraulics are very expensive and prone to failure, and even more difficult to raise into the hull for sailing or motoring..

    Sounds logical tonight - tommorrow - who knows :)
     
  8. captaintrue
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    captaintrue Junior Member

    A topic that I've mulled over here and there. I've even considered metal conveyor under the belly of a boat to make it easier to bring onto shore. A cat with retractable or removable wheel system (even small wheels--not all of them have to have 'drive' to them) would probably be idea on a cat.

    Trailerable ~= Amphibious.
    Anyways, if you think about it a trailerable multihull is essentially amphibious. Key thing if your catamaran, pontoon boat or trimaran is trailable AND is large enough to carry an ATV or a motorcycle or tractor or other machine capable of pulling it onto shore, you can have the best of both worlds--of course you'd need to get the ATV, motorcycle or tractor on shore via a tender. I'd give extra attention to hulls/skegs/floats toughened up in the forward sections for anything that I'd bring onto land frequently.

    Adding A Winch.
    Also, putting a winch on a boat could allow it to pull itself onto shore. One could go out from the boat in a tender, find a solid tree/post or the like and winch a boat onto shore. With the right lay of land one could use the same winch to get it the water again.

    ***
    In any case, IMHO worthile would be the effort of making a hull capable of withstanding repeated grounding.

    A cat, tri or pontoon boat would probably be a lot easier to add wheels to than a large monohull.

    Also a powered wheel system (rather than a passive trailer or winched system) requires a bit more engineering and complexity. A towed or winched trailer or wheeled system ought to go a long, long way. Whereas a powered wheel system--as nice as it might be the complexity seems to be a bit much especially in view of the impact saltwater might have on even readily available components taken from buses or cars.
     
  9. rambat
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    rambat Member at large

    Amphibian

    One of my favorites is the Orbiter, the design had a specific mission. IMHO amphibians need to be designed around their desired operation. Many try to be a great car and a fast boat but must compromise in the end. The Orbiter had to be designed as a liveaboard and a RV. Check it out at:

    http://www.dobbertinhydrocar.com/Orbiter On Location (Water).htm
     
  10. Jimbo1490
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    Jimbo1490 Senior Member

    Having wheels wet all of the time (obviously) ruins any hydrodynamic efficiency such a craft might otherwise have. Thus the piss-poor hull shapes chosen by amphib builders; since it doesn't matter much they just make it pointy on the front, seaworthy and comfy/functional on the inside. But that's hardly a way to design a yacht, IMHO.

    Why not have retractable wheels, you know, jet aircraft style? These could retract into wells or recesses built into the hull and be covered by a valance door when retracted. Or a sleek bulge could be faired onto the hull containing the retractable wheels. Either way, you get to have a real efficient boat hull shape when you don't need the wheels, which is most of the time.

    I've attached a couple of pics of a Mitsubishi MU-2 for examples. The subject aircraft came both ways; with faired bulges that house the retracted gear and with the gear retracting into the hull proper.

    Just as with aircraft, the valance doors need not be strong enough to stay attached if the wheels were extended under way; we just don't do that as it outside of the operating envelope :p They are only deployed when the craft is ready to 'land'.

    Jimbo
     

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  11. rwatson
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    rwatson Senior Member

    I have been mentally designing all sorts of methods , major considerations of weight and the interior room that is taken up with all the transmission, axles, controls etc is a real problem.
    I have considered aluminium versions of the old all metal tractor wheels, 4wd and agricultural wheel items, rubber tracks etc etc.

    At the moment, my mind is set along the idea of 'skis' or powered 'rubbing strips'

    Imagine, if you can follow my twisted logic, the bottom of a hull having 4 longitudinal substantial strips of aluminium (or solid 'plastic' or whatever). 2 on the port side, two on the starboard
    These 'skis' strips are like rubbing strips, faired to allow minimum disturbance in water flow, but much wider. They could even be set flush with the hull in grooves.

    The difference to normal rubbing strips ends when these 'skis' can be extended away from the hull by about 6 inches or so (with what? - perhaps half a dozen hydraulic pistons like outboard raising mechanisms), raising the hull. They can also be pushed longitudinally towards the bow, or towards the stern

    So, on beaching, they act as hull protectors, then the crew apply power to every second 'ski', This will lift the boat say 6 inches, and then power is applied to push the strips longitudinally to the stern, causing the boat to move forward.

    Then the previously unused set of 'skis' lift the boat again, allowing the first set to be repositioned forward. This second set is then moved to the stern causing the boat to move forward, and the process is repeated.
    The ski's on the port and starboard sides can be operated independently to allow steering.
    The concept is identical to a skier walking on skis, except the ski-poles would be replaced with a second set of skis. (like someone having no arms but 4 legs, all with skis on them)

    To my mind, this overcomes a few of the problems inherent in other concepts.
    1) The major cost and complexity of tilting whole hulls.
    2) Maximum surface area of contact with sand to prevent bogging.
    3) Low down weight with minimum moving (wearing out) parts like bearings, rollers etc
    4) made of materials that are not going to fail in marine environment like lots of little roller wheels on tracks
    5) Assistance in protecting the hull during grounding
    6) minimum intrusion into the hull
    7) simple hydraulic drive mechanism with little room taken up in the hull
     
  12. Jimbo1490
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    Jimbo1490 Senior Member

    Yeah, I get it. It's not unlike the locomotion use by walking dragline excavators.

    Jimbo
     
  13. rwatson
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    rwatson Senior Member

    Oh wow - it has been done! Thats great because there is half a chance it might work.
    I still am wrestling with the method of activating it - something low maintenance, easy to install, robust.
    For the lifting mechanism, maybe 5 or 6 hydraulic thingos on a hydraulic line or perhaps some sort of cam operated by a screw arrangement ?
    Any ideas appreciated.
     
  14. Pericles
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    Pericles Senior Member


  15. kach22i
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    kach22i Architect

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