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Recycled Propane tank floats

Home Forums Archive Structure Designs Recycled Propane tank floats

This topic contains 17 replies, has 9 voices, and was last updated by Profile photo of Jesrad Jesrad 4 years, 4 months ago.

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    Profile photo of jack.tinsley

    I am interested in building a 100′ by 50′ floating island out of used 500 gal propane tanks. They are 3′ dia x 10′ long and weight 800 lbs. I am planning on using 50 of these, the layout would be: 10 in a row, 5 rows spaced and braced. Total flotation of the system seems to be around 75 tons, I would like to add 50 tons of buildings and equipment. The unit will be self propelled by two modified dozer boats at the ends. Looking to move in fair weather at 1 to 2 knots.

    I live on the Queen Charlotte Islands, Haida Gwaii, in British Columbia. This “eco-island” would ply the waters surrounding the island, maybe only moved 50 miles at a time every month or so. Only on fair weather days and anchored in protected bays.

    My questions are:
    Do you think I am correct in my flotation calculations?
    Is the layout one that would serve best?
    What would be the simplest and lightest bracing, ( 8’spaces between rows )?
    What issues do you think I may run into or haven’t covered.

    Thanks for any comments and thoughts in advance.

    Profile photo of tusavision

    What’s the justification behind your numbers? Do you have 165 five hundred gallon propane tanks already? 2 bulldozers?

    Why do you need 75 tons of displacement? Pushing a 50’x100′ rectangle through the water isn’t exactly a Honda Civic. Are you prepared to pay the operational expenses of mobilizing such a monstrosity?(it’s not gonna be very fuel efficient)(if you chain the platform together in to narrow modules, and zig zag them together, that would allow you to “uncoil” for traveling.)

    I don’t mean to patronize, but that’s a very ambitious project, and calculating displacement is elementary by comparison. To get someone to comit serious brain time to your questions: you may want to demonstrate you’re 100% serious, and that this project you speak of is viable.


    you are possibly looking into the wrong direction when scanning for problems – of course you can build that float – no matter what spaces, no matter what distribution, all will work, of course buoyancy is enough if you put enough tanks no problem to expect on that front.

    Just keep in mind – the steel quality of a propan tank is NOT made for seawater – the life expectance of the float may be half or less of a industrial barge. Ask for a quote for sandblasting such a float in a shipyard or drydock (have a special look at the “additional handling cost” for not being standard barge) get a clear picture what maintenance cost you are up against – also put two tanks soldered together in seawater tomorrow and let them there for a month to get a clear picture how often you will have to go to drydock …

    Also read the story of dangerous Don. at:..seasteading.org/interact/forums/community/feedback-tsi/lets-get-forum-back-track


    Profile photo of jack.tinsley

    To Ellmer:

    Thanks as well for your encouraging thoughts. I had first looked at using standing dead cedar trees as a log barge, we do have plenty up here, but between toredos and constant sinking it was not a good alternative. I agree that maintenance is an issue in any structure and also that concrete floats are definetely going to be less maintenance. The issue I ran into in building them was the up front cost and logistics of being able to build them in a modular sense so they could be built away from the water and assembled at the water when done.

    I am interested in looking at the scenario again with some good input and advice from you. What do you think it would cost to build a 100′ by 50′ concrete float with a positive flotation value of 75 tons. How much material would I need, I have to calculate in this intense shipping costs to get such material to the Queen Charlotte Islands. Could it be economically viable to do in semi truck size modules so I could use my existing warehouse to build them, then truck 50 kilometers..

    I have also looked into steel barges, although they are generally already 30 years old and still expensive to purchase used. So in that sense I agree that an old steel barge is already at it’s corrosive prime. Even though it appears that Dangerous Don’s barge did not sink, I wonder how old it was before he got it and how long he has sold his bait from it.

    The fact that the tanks I have been negotiating for are already in the area and are not rusty condemmed tanks is a plus for my Northern BC venture. They are 1/4 inch thick and never been in the water, so for tanks, shipping, sandblasting, epoxy painting, bracing and zincs, along with the truck trips back to the seaside for reassembly I have calculated about $20,000 total cost for the float alone. The housing and stuctures that will be put on top will also be modular, so if in the worst case scenario a complete float failure were to happen we could move the structures to a new float.

    I have built another house float up here using the same steel tanks and it has been in the water for over 5 years with no noticable corrosion or leakage. It is all about how you protect them I agree, they do pretty good with all those 40 year old and older tankers running around the world that are built out of steel.

    I am interested in hearing some of your success stories with concrete floats, are they ferro cement, do you use extra floation inside them, and again what would the cost to build in my dimensions be.

    Profile photo of jack.tinsley

    Thank you for taking the time to further explore the possibilities of my endeavor.

    To tusavision:

    As stated, the 100′ by 50′ float will be built with 50 500 gallon propane tanks, each with a buoyancy of approximately 1.5 tons.
    I have made a deal with a local propane tank business to buy the tanks for just over scrap price of $75 dollars each. They are not failed or rusted cylinders they are tanks which have been caught up by new government regulations that state they need to be 250 psi rated and are only 200 psi rated so cannot be refilled. This gives me the base for the platform at a cost of $3,750. I am including another $10,00 in the budget for steel bracing, sandblasting, epoxy coating and zincs and another $5,000 for shipping to and from my warehouse were I will build the modules. The “dozer boats” are not bulldozers, they are small tugs used in the logging industry to boom logs. There are many used ones up in the Charlottes now because logging has tapered down to almost nothing. They are very economical drive systems, I have looked into hydraulic drives and single large tugboats but find one dozer mounted on each side would give me the best control in adverse conditions. They can be bought for under $4,000 each. I am only planning a 1 or 2 knot cruise speed so they will do the job with power to spare.

    We would mobilize the floating Island about 3 or 4 times a year to different locations around the islands up here, no more than 150 to 200 miles a year.

    75 tons of displacement gives a usable 50 tons for structures, equipment and landscaping, it will be built to look like and island not a fishing lodge box shape but more closer to nature, yet still sleep up to 24 people and have a greenhouse, chicken coup, beach and a light house for my accommodation. It will be dubbed “eco island” and be used to promote sustainable living and be a tourist attraction for the area.

    The structures will also be modular built and although I like your idea of chaining them together and uncoiling for travel it would not be feasible for the design I am interested in.

    I appreciate your patronage and your realization of the ambition needed and scale of the project, but I have the time and resources and will self fund the venture, about $150,000 when finished, starting this spring, figuring on just over a year to build.

    I have been researching and gathering as much information as possible over the last 6 months and find this forum to be one of the most like minded and adventurous group out there and really would appreciate any more input you have on the project.

    Please continue to think for us all.

    Profile photo of tusavision

    That seems like a good price for those propane tanks. Waterproofing would be difficult but not improssible. The nice thing about your idea is that the propane tanks double as pressurized gas storage.(although probably not breathable air) If you can water proof them while leaving the valves exposed: that functionality would come in handy. By mounting some of the propane tanks with the valve facing down under water: you can pump oil in to them using a hydraulic pump(to a pressure of 200 psi) and you’ll have a variable buoyancy system for storm weather. By filling them with propane: you have a source of propulsion(can your bulldozers be converted to run on propane?) heat, and power. By filling them with air: you can use them as air compressors for air-tools. I generally prefer compressed air to batteries simply because it’s easier for you and me to hillbilly together an air compressor and buy some air tools from harbour freight than it is to do the same with solar cells, batteries, and electric motors. I remain unconvinced that the efficiency gains of modern electric power justifies the complexity. Particularly when people are experiencing lithium ion explosions to rival boiler tank explosions from a safety standpoint.

    Cheap hydraulic pumps can be found for $10(automotive oil pumps) – $50(log splitter)

    Even on a concrete submarine: I’d want to have a few propane tanks for the purposes such as above.

    For $4,000: you stand to make a good return on your investment if you can figure out a way to waterproof them.


    Jack i have to agree with tusavision that the price for the tanks is very good, especially if they are new. I also would not dismiss the posibility that the steel of those tanks is by far better than normal shipbuilding steel and rusts much less, so you might in fact be far better off with the tanks than a standard steel barge – especially a old and used one in this sense your opportunity to aquire a large number of high quality low cost steel floats is unique and it may make sense to go for it – especially if you have a ealier pilot project that shows that corrosion to expect is less than a typical barge.

    When thinking in project cost the option of building the modules far from the waterfront is key as a waterfront building place is among the most important cost factors. So if you do not have property with deepwater waterfront access already, probably the best thing you can do is make the modules in a size and weight that you can move (and load unload) them with a (semi) truck and without a crane. Which limits them to 2,4m maximum size.

    I have choosen modules of 1m. If you live 50km from your building site you will probably perfer to have a module size that allows you to crawl in and sleep in a modul, store your tools and food inside, etc. (the module is the building camp) – so you could go for 2.4X 6X 2m or something like that – depending on the load capacity of your truck solution and the load / unload solution with a tripod.

    Your situation is also a bit different from mine for climate reasons. My plan is to have a single layer flat float and put a light “tent like” structure on it to shelter me from sun and rain – i live in the caribbean and build in the bay of cartagena – i get from your mail that you plan a kind of “heavy house” on top of the float. You might go for container sized modules and combine the modules to something like a container house – that provides you a safe enclosure without investing into a “additional structure on top”.

    What we do at European Submarine Structures AB is not the usual styrofoam encased in concrete that is used widly for houseboat floats. We do concrete shell building. If you do it right a concrete shell of only 5 cm wallthickness is already completly waterproof and bone dry on the inside. The thicker the wall the less prone to seeping it is. The impermeability factor is not increasing linear but geometric .

    “Ferrocement” is a meshwire based boatbuilding technique that is known by the public due to a lot of examples of poorly built hulls with problems – to get it right you must really do it right it is most of all a question of craftsmanship.

    I personally trust concrete shell applied with cast technique a lot more than ferrocement, especially what concerns long term life expectance. But as said before, you can not go below 5 cm – and this is already pushing the extremes – for a first time project i would recommend 10cm wall thickness minimum. This is too heavy for boats but applys well to heavy permanent floating platforms and submarine hull applications.

    At the moment we build cubes of only 5 cm wall thickness here in cartagena that are bone dry at the inside, but this needs a almost scientific approach on mix design to come up with something that has sufficient impermeability to allow only 5cm wall thickness. You need to take your local cement sand and gravel qualities and do a lot of testing to figure it out. A concrete engineer can not give you a good answer as he is not really familiar with the special case of concrete floats – you have to do your own development.

    When it comes to numbers our current pilot projects is pointing out the following – 1 squaremeter of float (weight about 500 kg) floatability 500kg, displacement 1 metric ton, can be built at some 200-300 euro (here in cartagena) – with a light housing structure on top you get quite exactly the 331 euro per squaremeter living space (9squarefeet ) we announced earlier.

    So if i would build a float of 100 feet X 50 feet (33meter X 16meter) = 528 squaremeter – this would cost some 174.000 euro – including the raw housing structure on top. This means a room and space equivalent of a 528 squaremeter apartment (528 square meter = 5 683 square foot apartment)

    The buoyancy would be some 264 tons so the structure on top could be some 100 tons of weight .



    European Submarine Structures AB

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    With separate metallic flotation elements it would probably be smart to build the platform so that the elements can be removed one by one for periodical maintenance with a minimal amount of work (meaning no divers or other expensive equipment).

    I.e. make the platform so that the floor can be removed in sections and the specific tank underneath can be lifted out or simply pop up by its own buoyancy and then overhauled and put back, without interrupting the general activities of the platform.

    As for the overall economics or feasibility of such a project, I haven’t got a clue.

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    Carl, the maintenance problem is one of the central problems for any permanent floating structure, boats and ships have a shore based “maintainance infrastructure” in place that consists in shipyards, slipways, drydocks, craning, travellifts, that allow them to deal with that problem. Happens that a float of the size we are talking about can not use this kind of maintenance facility due to its weight and size and structural charackteristics. So you have to solve it somehow else.

    Your “modular maintainence on the float itself” is a very good idea that can work very well for steel floats. If you have cylindrical float elements you might even let them in place and just rotate them so that the underwater part comes up for repaint periodically.


    Profile photo of tusavision

    Carl, the maintenance problem is one of the central problems for any permanent floating structure, boats and ships have a shore based “maintainance infrastructure” in place that consists in shipyards, slipways, drydocks, craning, travellifts, that allow them to deal with that problem. Happens that a float of the size we are talking about can not use this kind of maintenance facility due to its weight and size and structural charackteristics. So you have to solve it somehow else.

    Your “modular maintainence on the float itself” is a very good idea that can work very well for steel floats. If you have cylindrical float elements you might even let them in place and just rotate them so that the underwater part comes up for repaint periodically.


    I like it.

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    Might I suggest placing the tanks in rows, end to end, something like segmented pontoons? Should give a better directional stability, during movement, and could use a combination of anchors and a sea-anchor, to keep turned into the current…

    I don’t suggest using any as gas-storage, as adding compressed anything to the tanks will reduce buoyancy (added mass is still added mass).

    Might consider spray-on truck-bed liner (Rhino-Liner), for waterproofing… It has proven durability in exposure to light, water and abrassion conditions…

    If the whole base is modular, it could be disconnected and reconfigured into a single-file, like barges, for your moves, then re-assembled at the new location. That modularity could also be used to take segments in, for repair…

    Only problem is connecting/disconnecting, unless you use cleats/ropes/fenders between sections (like tieing multiple boats together), which creats another set of problems…

    If you are planning a single, large barge type structure, if the tanks are clamped in place (not welded), they could possibly be pressurized to reduce buoyancy, for removal/replacement, or flooded with water, then pumped-out (like a submarine ballast tank).

    Many possibilities! Might post some links to pics of the general idea and see what we can add to the design, just don’t let the nay-sayers get you down!

    Wish it was me. I’m trying to keep my land, in this crappy economy, and piece together a small farm… 17,78 acres is a good way to see what self-sufficiency I can work out…



    Never be afraid to try something new…

    Remember, amateurs built the ark, professionals built the Titanic.

    Profile photo of jack.tinsley

    I thank you all for looking at the project as I realize it is different from the normal seasteading threads in a number of ways. 1. The island will not be anchored in the open ocean. 2. It will be moved around the islands and passages up here only on fairweather days. Although the design will allow up to 30 people top stay over night, it is not really permenant living. It will however feature sustainable building and living conditions that will definetly showcase eco living. 4. It is a business model that is designed to make money by eco tourism and allow researchers and special interest groups an alternative to regular “hotel’ type accomodations while doing studies and projects. (we get a lot of that up here as Queen Charlotte Islands are dubbed the Galapagos of the north. )

    This sustainability is what is very common in this forum and I can see we are all learning from each other and thinking like minded.

    Back to the thread. Great idea’s and thoughts JLF and Wil.

    To give you a little insight to the propane tank float concept. I simply called one of the propane businesses that is on 100 miles away from me in a town of only 15,000 people. He has 88 used 500 gallon tanks and about 30 1000 gallon ones sitting in his yard. He just sent two truck loads of 40 of them to the scrap recycler at $75 each. If this is one little town and only one propane business, how many used tanks are out there???

    IN my case he has convinced me to use the 500 gal ones instead of the 1000 gal ones ( which would actually make more sense, fewer floats, easier to connect and so on )for several reasons: The 500 gal ones he has are caught up in a new law limbo over pressure and cannot be refilled so they are not uncertifiable by means of rust, leaks or damage. They are all from the same manufacturer so they are all indentical in size. The 1000 gal ones do get bought more often for fuel storage, oil and so on and garner more money $500 each is usual price. The big advantage in going 500 is also the fact that they only weight 800 lbs as apposed to 1,800 and can be moved by small crane trucks and forklifts, the 1000 need big equipment to move them around. The last thought is more of a question, the 500 gal tanks are 3 foot by 10 foot, the 1000 gal ones are 3 foot by 16 foot. Not double the size as one would think. Does this do us better in displacement because the 500 ones, doubled up to 1000, are actually about 20 % bigger??

    I really like and agree on your thoughts about getting double use of the tanks, compressed air, storage of other sorts and the fact that you can ballast them if needed. I also like how we are thinking about the maintenance, I actually have the Rhino liner in the back of the used truck I bought, the guy didn’t put drain holes in it and when I park facing down hill the truck would start looking like a hot tub, and tough as nails as well.

    My thoughts on the issue are this: Properly prepare the tanks then 2 part epoxy paint them. Weld brackets (they come flared off so the are inert and non explosive he guarentees me) to each tank. line them up ten in a row end to end, run two 100 foot section of steel beam down eack side of the tanks and bolt them to the beam. Build 5 rows, spaced about 8 feet apart, this gives me my 100 by 50 float size with 75 tons of lift, run braces across the pontoons to connect the five rows and this will also provide the structure with a sub floor to connect to.

    Now, as you have said, if there is a problem with one of the tanks, you can simply unbolt it, take it out and fix or replace it. I was thinking of running a pipe down into each tank at the old valve location to allow to drain or fill the tank if needed.

    Here are some of the problems I can see.

    Finding the best method to stop the inevitable rust. The epoxy paint has shown good results in a float home we built in this method, it has been in the water 5 years and looks good, although I haven’t dove under it and examined it for flaws. ( which I will now ) But is there a cheaper better way.

    I am not an engineer, so how big do the beams and cross links have to be. It would certainly be nice to be as light as possible But:

    If the float ever got caught by a low tide and was point loaded anywhere, tons of weight would be in one spot and bend or damage it, needless to say a collision with anything would not be good either. I was thinking the maybe wood beams would be better for flex and easier to replace if broke than trying to straighten steel beams.

    I am trying to find a real simple free drawing software so I can start doing layouts that we can all see, any ideas?

    Would appreciate continuing the conversations, Tanks!!!

    Profile photo of Farmer

    Bump for relevance.
    That is to say I am posting only to keep this thread at the top of the “recent posts” list because I consider its content worthy of attention.
    Since I have no actual content to add allow me to say that while large gas tanks are perfect many discarded objects (shipping containers, wooden dressers, mattresses, refrigerators and telemarketers) could be covered with an inch thickness of concrete and be used in the same way.
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