Barge questions

Discussion in 'Boat Design' started by Magnus W, Oct 25, 2019.

  1. Magnus W
    Joined: Nov 2017
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    Magnus W Senior Member

    I need a barge and while I'd be better off just buying one I can't really motivate the cost since I've come across some pipes that I can get for free.

    The pipes have a diameter of 1100 mm and are 12 meters in length and has a 14 mm thickness. If my math is correct that means a mass of circa 380 kg per meter and a volume of 0,95 cubic meters per meter which in turn means that I have about 550 kg buoyancy left (per meter) to carry superstructure and whatever I chose to put on the barge.

    If I estimate a superstructure and equipment mass of 0.5 times the pipe mass the barge – for 12 x 4 meters of pipe – is 27 tons with a buoyancy reserve of 18 tons. 18 and a 50 percent marginal is 9 tons which is lower than the typical square block style barge of similar size but well within my needs. Also, I think it can be lighter as well as get more buoyancy quite cheap (the latter by adding blocks of expanded polystyrene between the pipes and the deck).

    In order to make the barge easy to build I'm considering having beams water cut from sheet metal (red in pics) and simply welded to the pipes. (Not in the pics but there need to be X-bracing also. As well as stringers to reinforce the deck.)

    How thick should the beams be, will 10 mm be enough?

    How thick should the deck be, 5 mm?

    Any suggestions on what steel to use? The pipes are what they are but they're plenty thick and can be protected by anodes. But the rest? I would like to have a decent corrosion resistance but I'd also like to paint it so corten won't do (unless I'm mistaken that corten steel doesn't paint well).

    Topview.png

    skiss.png
     
  2. BlueBell
    Joined: May 2017
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    BlueBell Ahhhhh...

    Hello Magnus,

    Are you going to cut deadrise into the ends of the pontoons for hydrodynamic benefit when towing?
    This will reduce your static and reserve buoyancy.

    As is:
    950kg per meter minus 380kg equals 570kg buoyancy.
    Looks like you've got 4, 12m pipes.
    That's 48m X 570kg totalling 27 tons buoyancy available.
    1/3 of 27 tons is 9 tons maximum static load.
    Because round pipe has diminishing buoyancy after 50% loading, you need to keep 2/3 as reserve buoyancy in order to avoid a rollover.
    On that note: You'd be better off with a larger space between the second and third pipe moving two pipes to each side, against each other.

    What are you going to use the barge for?
    How much does EVERYTHING you're going to put on the barge weigh?

    I don't know the answers to your other questions, sorry.
     
    Last edited: Oct 26, 2019
  3. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    Just some random thoughts....
    A pal of mine built a 20 metre power catamaran here some years ago using large diameter steel pipes (which he happened to have) to form the lower halves of the two hulls. He split the pipes in half longitudinally, so that they were semi-circular in cross section. He then used plate to 'build up' the sides before adding a flat 'deck' on top of each hull. He then used some smaller steel pipes as cross beams to connect the hulls together. Each hull had a nice pointed bow, with shape at the stern as well. It is propelled by two Perkins 80 hp diesels on shaft drives.

    Re your drawings above - how about splitting your pipes in half longitudinally (and horizontally) so that you have four hulls (a quadmaran?).
    Then add your deep transverse crossbeams, and on the two outer hulls build up the freeboard with flat plate, up to the top of the cross beams.
    Add longitudinal plates between the hulls attached to the undersides of the cross beams, to make the 4 hulls all watertight.
    Then add a deck on top of the cross beams.
    If you use complete pipes, the 'top halves' are not really doing a lot of good in the configuration you have shown; they add a lot of weight, yet as the draft increases past the mid span of the pipe, the rate of increase of buoyancy rapidly decreases.
     
  4. gonzo
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    gonzo Senior Member

    If you cut the pipes, welding the edges would be more efficient. The bow and stern can simply be a plate with the bottom edge cut to match the edge of the pipes. However, to put that amount of work and money to save in steel may not be a good idea. Have you tried swapping the pipes for plate to a steel dealer?
     
  5. Magnus W
    Joined: Nov 2017
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    Magnus W Senior Member

    Yes, some deadrise in the front end but mainly to make docking on a shore easier, not so much for hydrodynamics (it will suck regardless).

    Like this
    Deadrise.jpg

    The amount of load I'll take will depend on what the barge is capable of. But in general terms not so much, it's more of a work platform.


    I know round pipes are fare from ideal but I get them for free and I have a friend who has a welding company that work with district heating. They can easily seal the pipes so that I have four high quality airtight compartments that I won't have to worry about for a long time. While I'm decent with all regular welding I'd rather have pros doing the floating part so that I "only" have to focus on superstructure.


    My thoughts too, I'd like to keep work and investments at minimum since it won't be ideal anyway. Good idea about swapping but these pipes are old and nobody knows what they are made of so they have only scrap value (that's why I get them for free). Since they were intended for use in a power plant I assume they're good quality but that doesn't mean anything when the don't come with documents to prove it.
     
  6. Magnus W
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    Magnus W Senior Member

    Maybe for like this?

    With foam.jpg
    If I make the transverse beams (red in pic) with from 10 mm sheet metal that is circa 220 kg per beam. Let's space them 1000 mm apart which equals 13 beams and 2860 kg.

    66 square meters deck at 5 mm is 2650 kg. Then add 2000 kg for webbing and other reinforcements such as stringers for the deck etc. In total 7510 kg so 7,5 tons.

    Since the deck will have to be raised from the pipes I can fit styrofoam (blue in pic) between the pipes and deck. Higher density xps (more sturdy) weighs 28 kg per cubic meter so if I add 100 mm below the deck it equals 6,4 tons of buoyancy. I know it's not going to do me any good normally but it's hardly any weight and it gives me a little safety margin should I be unlucky or do something stupid.

    Anyway. 12 x 4 x 380 is 18240 kg but lets round it up to 19 tons since the pipes will have to be capped. Plus the 7,5 above and I'm at 26,5 tons. With a total buoyancy of 45,6 tons (not including styrofoam) I have 19,1 tons left which by BlueBells 2/3 rule (which makes sense) means 6,4 tons of useful load.
     
  7. Blueknarr
    Joined: Aug 2017
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    Blueknarr Senior Member

    Don't bother adding foam in your blue areas. It won't add any safety margin. Your safety is to keep the water line well below the midpoint of the pipes. Adding foam in the quasi triangle between the bottom of the tubes, or connecting them with steel plate would add safety buoyancy.
     
  8. BlueBell
    Joined: May 2017
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    BlueBell Ahhhhh...

    Yes, that is what I meant.
     
  9. BlueBell
    Joined: May 2017
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    BlueBell Ahhhhh...

    I got a little distracted there with pipe mass and buoyancy.
    Bad news, you have less static buoyancy available than I thought.
    The 1/3 rule for round cross section pipe is used up in the mass of the pipe alone!
    380/950 = 0.4 which is greater than 1/3 sadly.

    Cutting the pipe into vertical sections would eliminate the diminishing buoyancy issue with round pipe.
    Arranging them vertically would allow for a square barge which can make for a better work platform.
    But, it's a lot of work and material to cap the ends.
    You can cap the tops with the deck.
    But it's not going to tow as well as the original design.

    This free pipe may not be so cheap in the long-run.
    Cutting them in half, longitudinally, in the original arrangement, would help
    but it's still not going to leave you with much buoyancy.
     
    Last edited: Oct 26, 2019
  10. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    Magnus, one problem that you have is that the scantlings (tube thickness) for your proposed barge using these scrap pipes is a LOT more than what would be needed, even with a good factor of safety thrown in.
    So you will essentially be carrying around a lot of unnecessary deadweight with you.
    You mentioned that
    "The amount of load I'll take will depend on what the barge is capable of. But in general terms not so much, it's more of a work platform."
    You must have even a rough idea as to what cargo capacity you want the barge to have?
    Will it be self propelled (perhaps with a couple of outboard motors) or will it have to be towed everywhere?
    Will it be on inland waters, or perhaps coastal where the sea can perhaps get a bit choppy?
    It might be worthwhile looking around to see if there are any suitable small second hand barges for sale in Europe?
    This 16 metre barge in Sweden has been sold, but you could try contacting the broker to see how much it sold for, and ask them to keep an eye and ear open for any 'small' barges that fit your requirements?
    Ship - Evert - Shipsforsale Sweden - The Scandinavian Shipbroker https://shipsforsale.com/en/ships-en/shipid/124/barges-andamp-pontoons_5_evert

    Here is a 12 metre x 3 metre barge for sale in the USA for US$ 33,000; have you got an approx budget re how much you want to spend on your barge?
    https://www.oceanmarine.com/detail.cfm?Shugart-Sectional-Barges-40x10x5---File-#14706&product_id=14706&category_current=6&category_current_sub=24

    While these are also 12 m. x 3 m., new construction, for US$ 31,500.
    Truckable barges sectional https://www.oceanmarine.com/detail.cfm?40x10x5%2DSectional%2DBarges%2D%2D%2D10881&product_id=8299&category_current=6&category_current_sub=24
     
  11. Magnus W
    Joined: Nov 2017
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    Magnus W Senior Member

    Thanks for all the replies. I'm not going to build this no matter what, at this point I'm just running the numbers to see if it's feasible not. Using pipes, despite being a sub optimal design, is (was) only an option because they're for free.

    As mr bajansailor puts it, the pipes are way too beefy. I'll have to verify the pipe thickness is correct, so far I only have "they are like 14 mm". A quick search suggests that the standard 1100 mm pipe has an OD of 1118 and ID of 1098,94 which in turn means 264,8 kg/m.

    264,8 x 48 is 12710 kg. 12,7 tons + 7,5 tons (see above) is 20,2 tons unloaded.

    Also, I can use five pipes instead of four (cutting a bit of every pipe to make a fifth one), making the barge 9,6 x 5,7 (instead of 12 x 5,5 above) meters which would further reduce the superstructure weight from 7,5 tons to 5,7 tons so 18,4 tons unloaded.

    Assuming the above, is it still a no go?
     
  12. BlueBell
    Joined: May 2017
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    BlueBell Ahhhhh...

    OD of 1118mm, ID of 1099mm = 19mm divided by 2 = 9.5mm wall thickness, which is a long way from 19mm wall thickness you originally claimed.

    So your 380 kg/m should be half at 190 kg/m... but you're claiming now that it's 264.8 kg/m

    265kg / 950kg = 0.28 vs 190/950 = 0.20

    I guess you better sort out your numbers and get back to us.

    Question: "Assuming the above, is it still a no go?"
    Answer: Most likely, especially given your inaccurate numbers.
     
  13. Magnus W
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    Magnus W Senior Member

    I said 14 mm in the starting post and that's what I based the numbers on. "The pipes have a diameter of 1100 mm and are 12 meters in length and has a 14 mm thickness."

    I have asked the owner to double check the thickness since 14 mm seems a lot, given that the standard is 9,5. But maybe that's still to heavy?
     
  14. BlueBell
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    BlueBell Ahhhhh...

    Sorry Magnus W, my mistake.
    You are correct.
     

  15. Magnus W
    Joined: Nov 2017
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    Location: Sweden

    Magnus W Senior Member

    No need to be sorry, I appreciate you input as it's most welcome. I have only empirical experience from barges so opinions from a theoretical point of view are invaluable.
     
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