maximum ramp slope

Discussion in 'Boat Design' started by black boat, Aug 13, 2019.

  1. black boat
    Joined: Aug 2019
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    black boat New Member

    Hi all,
    We have a deck cargo barge with 30 m in length, trucks must move from barge to berth and unload their bulk cargo, and problem is difference of height between deck and berth. this height is 1m .what is the safe inclination? 15% --20% --30%??..thanks
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    Doesn't the tide come into the equation ?
     
  3. black boat
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    black boat New Member

    No, tide isn't in equation..I forgot to say that, I am not allowed to design long ramp.
     
  4. RAraujo
    Joined: Apr 2010
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    RAraujo Senior Member - Naval Architect

    Check also for the eventual effect on trim variations as the truck moves along the barge.
     
  5. black boat
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    black boat New Member

    thanks for your recommend, but that was considered, 1 m difference with trim by aft..
     
  6. kapnD
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    kapnD Senior Member

    The limiting factor in such operations is going to be the clearance under the trailers as they go over the hump.
    A folding ramp can double the span without getting outrageously tall.
     
  7. Phil_B
    Joined: Mar 2019
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    Phil_B Junior Member

    You need to cater for the approach and departure angles too - imagine a straight stick jammed under the front wheel of the vehicle and raised so it touches the underside of the front of the vehicle (or the sump or whatever the lowest part of the vehicle happens to be). That is your approach angle and the ramp must be a shallower angle than that otherwise the front of the vehicle will hit the ramp before the front wheels do.

    The departure angle is the same except for the back of the vehicle and again, the back end of the vehicle will be damaged as it leaves the ramp onto the deck of the barge or the ground.

    Plus, as kapnD said, you don't want the belly of the vehicle to ground out either.

    So ... depends on the vehicle (or trailer) you are using.
     
  8. Deering
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    Deering Senior Member

    If you get to the point where the trucks might be bottoming out on the ramp, I’d look carefully at traction, assuming a wet, slimy ramp. That may be your limiting factor.
     
  9. gonzo
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    gonzo Senior Member

    The limiting factor is the ground clearance in the trucks. The transition from the road to the ramp will be the determining factor. If the trucks have air suspension, they can be raised to allow for a higher hump.
     
  10. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    The ramp must be designed so that any truck, even if it does not have an "air suspension", can access the ship. Designing a ramp only for a certain type of truck is a mistake. In other words, designing a ramp that only works for trucks that can undertake a higger hump is a mistake.
     
  11. Magnus W
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    Magnus W Senior Member

    Here most barges and boats designed to be loaded with trucks etc use hydraulic ramps. The ramps (or should I say ramp) is pushed down with the tip over the jetty, thus in effect lifting the bow of the boat/barge up until the desired angled is achieved. 30 meters is not that much and we have many in that size and it works very well. This method also make for a stable loading/off loading as the boat/barge ramp doesn't move so you really don't feel going from land to boat (much appreciated with the truck drivers). The best ramps are two folded (so you can arch them), then you can compensate for a large difference in height without the hump problem.
     
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  12. TANSL
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    TANSL Senior Member

    There and everywhere. I can't think of any example of a big boat with electric ramps or any other type that isn't hydraulic.
     
  13. Magnus W
    Joined: Nov 2017
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    Magnus W Senior Member

    If so then I dont see the problem. Lift the bow of the 30 m barge 1 meter and the angle is 1,9 degrees. Arch the ramp and it will be even less. (And this is not taking into account that the ramps ad more length to barge, further reducing the angle.)

    Trim difference while loading/unloading will not be a problem unless you do something really stupid which would affect stability more than be a problem for the trucks as far as angles go.

    What is the empty weight and load capacity of the barge? Maximum deck load?
     

  14. jehardiman
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    jehardiman Senior Member

    There is an ISO/NATO spec for shipping ramps if I recall correctly from the days I packaged items to be shipped. I know every aircraft has it's own spec sheet which doesn't match the ISO spec.

    Edit: Quick google
    ISO 6812:1983(en) Roll on/Roll off ship-to-shore connection — Interface between terminals and ships with straight stern/bow ramps
     
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