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  • Barge Tonnage

    I know the tonnage of a barge (894). How do I figure out the weight capacity of the barge? Since tons are calculated in different ways based on location, which kind of ton (long, short, or metric) would I even be using for a US barge operating in California? I'm trying to determine whether a barge that shipped materials such as sand and aggregate (all with different densities) ever carried a load greater than its capacity.

  • #2
    Re: Barge Tonnage

    The tonnage of a barge may not be tons of weight, but tons of volume.

    If the tons in question was weight, then California would most likely be using the U.S. short ton.

    There is also the Register Ton (RT) which is a unit of volume used to measure the cargo capacity of a merchant ship. It is equal to 100 cubic feet.

    There is also the Displacement Ton (DT) which measures the volume of sea water a ship displaces. It is equal to 35 cubic feet.

    And lastly, there is the Freight Ton (FT), Measurement Ton (MTON), and US Shipping Ton which are 40 cubic feet, and the British Shipping Ton which is 42 cubic feet.

    Now, did I help any, or just make things worse?

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    • #3
      Re: Barge Tonnage

      I'm pretty sure that in this case the tonnage is volume.

      I've done some research trying to figure this out and as I understand it the ton weight was originally derived from the weight of a fixed number of casks ful of liquid, or somethinglike that. Is there a standard density I can use with the tonnage/volume of the barge to determine the amount of weight the barge can be expected to handle?

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      • #4
        Re: Barge Tonnage

        Way back in the middle ages the unit we now call the Register Ton was the number of wine tuns that a ship could carry. Now its simply defined as 100 cubic feet.

        But I dont see how to determine the maximum weight a barge can handle.

        You can use it to determine the maximum weight it can carry. Just not sure how you could tell if that would sink it or not.

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        • #5
          Re: Barge Tonnage

          Is there a way to establish a relationship between barge tonnage any deck area (sq m)

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          • #6
            Re: Barge Tonnage

            I am trying to create an excel spreadsheet that will allow the inputting of barge dimensions and then allow the input of the the draft measurements (then do some great excel math) and spit out a total tonnage. Please advise if you have seen anything like this, have anything like this, or have suggestions. My user name is an email address that yo can reply to.

            Thanks-

            MDB

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            • #7
              Re: Barge Tonnage

              A barge is a less complex shape than a ship, but it is still not a simple shape. I found a couple of examples of barge tonnage tables which might help you. But complex tonnage surveys are needed to produce these results.

              If you describe the hull shape as an area as a function of depth, to get total displacement, you have to integrate that area from the bottom of the hull to the waterline. You will need very detailed dimensions to determine the function. Ultimately, you can produce a table showing the change in displacement for a given change in draft (tons/inch). The barge will have a loadline at the maximum approved draft (minimum freeboard). Note the displacement will differ in salt and fresh water.

              The first example has a rough drawing and quite a bit of data on an example barge. The second is just a tonnage table:
              http://www.canalbarge.com/WebPublic/Main.nsf/e27f17a8cdf0cd5a86256af6006bbc27/f421e2a5e4c79cde86257242006bc3b5/$FILE/CBC%202261,%202263,%20&%202264.doc

              http://www.waxler.com/files.php?id=I...Yslj98uqktNRyQ..

              In the first example, note the deadweight (cargo) tonnage is almost twice the register tonnage (which is a volume)

              Comment


              • #8
                Re: Barge Tonnage

                I've looked at this a little more and I think it is not feasible to easily calulate the capacity of a barge. It doesn't have a single capacity. It has a range of capacities depending on the height of the center of gravity of the combined barge and cargo. Every barge must have a table for this but the calculations are complex.

                This booklet from New Zealand is helpful in providing an overview, but not the detailed calculations:
                http://www.maritimenz.govt.nz/public...Guidelines.pdf

                This Wikipedia article may explain metacentric height better: http://en.wikipedia.org/wiki/Metacentric_height

                In any case, whichever of three distinct limits occurs first is what sets the capacity (vs center of gravity):
                *Initial stability (metacentric height)
                *Static stability (at high heel angle, 35) and righting lever
                *Dynamic stability, area under righting lever curve.
                It is not clear to me how to calculate the last two and they seem typically to be the limiting ones.

                As explained in the NZ booklet, the calculations are done by a naval architect, and it is up to the loadmaster to stay within the safe area of displacement vs center of gravity curves.

                The barge (especially a deck cargo barge) has a higher capacity when carrying very dense loads essentially flush with the deck and a much lower capacity with light-weight material piled high on deck. A couple of example curves are shown in the booklet.

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                • #9
                  Re: Barge Tonnage

                  As mentioned above, rated capacity of a barge is pretty complex, but displacement at a given draft can be estimated well. A simple barge has straight sides and a flat bottom, but may be raked at bow and/or stern to reduce water resistance. The rake results in a keel length, L1, shorter than the deck length, L2. Width is W, and hull thickness T2, with thickness at the rake T1. This is shown in the crude sketch attached. (Can you tell electrical engineers didn't have to take drafting at my school).

                  If height is measured from bottom of keel, the barge area in a horizontal plane is L1*W at h = 0, growing to L2*W at h = T1 and above. The displaced volume is the integral of A(h)dh from 0 to the draft, d.

                  A(h) = L1*W + W*h*(L2-L1)/T1, for 0<h<T1
                  = L2*W for T1<h<T2

                  The integral V(d) vs draft is
                  V(d) = L1*W*d + 0.5*W*d*(L2-L1)/T1, for 0<d<T1
                  = 0.5*W*T1*(L1+L2) + W*L2*(d-T1) for T1<d<T2
                  The volume is in cubic feet if feet are used, cubic meters if meters are used.

                  To convert to mass, multiply by the density of water:
                  Fresh: 62.4 lb/ft (0.03120 short ton/ft)
                  or 1 t/m (note metric ton)
                  Salt: 64 lb/ft (0.032 short ton/ft)
                  or 1.025 t/m
                  This is the combined displacement of barge and cargo. For cargo only, calculate mass of barge at lightship draft (unloaded) and subtract.

                  Comment


                  • #10
                    Re: Barge Tonnage

                    But what if you just want to know what the deadweight of the barge is? For instance, if you knew all of the dimensions (except weight), but wanted to try and estimate how many tons of steel might be in the barge for scrap calculations purposes?

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                    • #11
                      Re: Barge Tonnage

                      Originally posted by Unregistered View Post
                      But what if you just want to know what the deadweight of the barge is? For instance, if you knew all of the dimensions (except weight), but wanted to try and estimate how many tons of steel might be in the barge for scrap calculations purposes?
                      See post #9. You need the lightship draft (barge unloaded, any water in the bilge pumped out). The weight is equal to the water displaced.

                      By the way, the deadweight is the cargo, crew, provisions, fuel, passengers etc, everything that adds to the lightship weight. The two added together are total displacement.

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                      • #12
                        Re: Barge Tonnage

                        How do you compute the net tons and gross tons on a particular size deck barge?

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                        • #13
                          Re: Barge Tonnage

                          Originally posted by Unregistered View Post
                          How do you compute the net tons and gross tons on a particular size deck barge?
                          Posts 7, 8, 9 might help. You can calculate what the load is from draft and dimensions, but not (easily) whether a load is legal. The actual rating of the barge is quite complex and includes factors like how high the cargo is piled above deck. The barge must be surveyed by a professional surveyor and have a load book.

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                          • #14
                            Re: Barge Tonnage

                            Deadweight is the mass that a vessel can carry - ie the total of cargo, fuel, stores, etc.
                            If you want to break up the barge for scrap then you want its lightship weight. If you can calculate the displacement (see above) when it's empty, that is the lightship weight.

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                            • #15
                              Re: Barge Tonnage

                              you need to get displacement tables for that paticular barge. often previous owner may have these. Then measure portside freeboard at forward and aft draught marks and midship, then starboard. Now add these six measurements together and divide by six to get the mean freeboard. convert to inches,then measure total molded depth of barge at midship and convert to inches. subtract mean freeboard from molded depth. This is your mean draught,refer to displacement tables for tonnage related to your mean draught.

                              Your 35x185 barge would likely be in the area of 15-20 short tons per inche of water it displaces.

                              hope this helps

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