How to figure how much weight I can put on my barge.

Discussion in 'Boat Design' started by lbjdockpro, Apr 23, 2016.

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lbjdockproNew Member

Its 10'x30'x4' steel plate barge 100% welded and the hull is filled with nitrogen gas. I was just curious as how to figure out how much weight the barge can hold with out being completely submerged.

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HeimfriedSenior Member

You have to know its volume and its weight to calculate the possible additional load.

Volume * Water Density * Gravity Acceleration * 0.9 = Buoyancy

Buoyancy - Weight (empty Barge) = Payload

The factor 0.9 is a factor of safety.

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lbjdockproNew Member

It has a inner structure made of 4x4" 1/4" thick angle iron that I don't know how much it weights. But I do know the weight of the plate siding which is10208 lbs. Theoretically there should be braces every 2' so I'd guess the inner structure to weigh 1600-1800 lbs. So over all were looking at about 12,000lbs with a volume of 1200'.

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Suppose that the barge is essentially a box. The box 10 x 30 x 4 would displace about 74,800 pounds of fresh water and about 76,800 pounds of salt water if fully submerged. Lets use Heimfrieds fudge factor of 0.9. So the absolute maximum numbers would be about 69000 for salt water or 67000 for fresh water. Subract the 12000 pounds that you estimated and you have a figure of about 57000 for salt and 55000 for fresh water.

Of course you would not dare load the barge all the way up to the deck line. Maybe halfway. So halve the numbers and you will have a SWAG notion of possible load.

Take particular notice to the admonition that the barge may not be very stable if loaded even to half capacity. Where and how you use the vessel is a serious matter not to be dismissed. If the barge is filled with nitrogen then it must be presumed that the cargo will be deck loaded only. That is a condition that can be dangerous if not carefully planned.

You can do your own arithmetic by knowing that a cubic foot of fresh water weighs 62.4 pounds and a cubic foot of salt water weighs 64 pounds. We used the fudge factor of 0.9 with the presumption that the ends of the barge may be tapered and so it is not a plumb sided box and the displacement is therefor somewhat diminished.

I strongly suggest that you consult a qualified naval architect (which is not me) to sign off on the barge so that you can have some protection from liability suits and/or Bureaucratic red tape.

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rasorincSenior Member

why was it filled with nitrogen gas? And how do you know it has not leaked out or will in the future. Is the whole box filled and to what pressure?

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lbjdockproNew Member

Thank you mess about. The hull was saturated with nitrogen because its lighter than air and without oxygen carbon steel can not oxidize. The barge right now has a 20 ton Kubota excavator, airman air compressor, and a Lincoln sa-200 welder on it. She handles all the weight very well. I suppose if it ever was punctured id walk up to the job site missing a boat and a barge, but shes got a 1/4" sheet metal hull and we haven't been easy on her. I'm planning to start dredging soon and I was curious to my boundrys for a 10'*30'*4' section of the barge.

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bhnautikaSenior Member

So do we think, Pounds per inch immersion (PPI) in this case wouldn't easier
L(ft) X B(ft) X 5.333 (salt water)= PPI
LXBX5.2 (fresh water)= PPI

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cmckessonNaval Architect

You are getting good advice that stability is the tricky part. That barge may be able to LIFT 40,000 lbs, but above 20,000 lbs you run a real danger of tipping over.

Chris McKesson

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SamSamSenior Member

Pay particular attention to messabout's post. SWAG means Scientific Wild Arse (***) Guess.

Watch this and notice that it's a large, supposedly engineered operation and that nowhere is the barge even half submerged, but still, it all went to **** very quickly.

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PARYacht Designer/Builder

This isn't a very fair comparison, as an inappropriate load setup was employed and mechanical failures resulted during the lift, plus the operators also screwed the pooch with the lift.

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waikikinSenior Member

That's a fair movable weight(? chained down?) in the excavator considering the the bucket & arm at extension, it's really not a big barge by any means at 30' x 10'. Working over the "bow" with that might be fine... are you dredging with the excavator or using other gear for that?

Again, this isn't a fair comparison but just shows that sometimes stuff can go wrong, I like that the driver tried until the end to climb out before bailing

All the best in your endeavours from Jeff

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SamSamSenior Member

So here you have a guy with a 10 foot wide barge, 4 feet deep, asking how much he can pile on top of it, not in it, but on top of it, before it submerges. I figure the barge has about 9 tons displacement per foot, so even with only the 20 ton excavator on it the barge is already sunk more than halfway. Add the airman air compressor, and a Lincoln sa-200 welder. Then add the weight of the steel barge itself, being maybe 6 tons. Consider that the op apparently thinks the lighter than air nitrogen will give more loading capacity, and that he doesn't generally seem to know much about what he's doing as far as working off of a barge.

I don't know much about working off a barge either, but I would think twice about swinging the bucket of a 20 ton excavator off to the side of a 10' wide, 4' high barge that was almost 75% submerged to begin with, and then piling up a mound of unstable saturated mud until the point of submersion, but that's just my uneducated opinion.

So, what is a fair comparison to what the op wants to do?

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lbjdockproNew Member

I never said the lighter than air nitrogen will give more loading capacity. I don't believe it gives it more buoyancy that's just how it was built. My uneducated opinion would be looks like I'm doing quite we'll for not knowing much about working off a barge. I'm new I don't know what to do-Joe Dirt. I don't think you know much about making assumptions. Sam Sam. The two barges you see below are two 10'*30'*4' sections per barge. I was wondering how much weight a individual section could handle but thank you for all your other concerns. I understand your trying to keep your criticism and sarcasm sharp but this isn't the place for that I bet you would have better luck on Facebook samsam.

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14. Joined: Jan 2006
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waikikinSenior Member

Hi lbjdockpro,
They look like pretty neat modular units. Your pictures speak volumes. Looks like you're already pushing the limits at times. Not sure what the go is where you live but in Aus there's regulation on working freeboard & inclination etc. Dipping the deck edge is pushing a bit hard from where I stand.
Barge & excavator operators don't usually wear suits except getting married or in court in front of the coroner, all you need is an extra aspect or two to the working day & the holes in the cheese might line up.... best not to be that guy.
I know your question was "how much to sink this" & not wishing you harm, I don't know how to apply the regs & calculations myself but would be getting some pro advice on your operation.

All the best from Jeff

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Mr EfficiencySenior Member

Yep, not a matter for guesswork, or could easily turn into an expensive or even deadly mistake. Hardly a routine stability calculation when you have excavators at work, applying forces with long lever arms involved.

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