Fiber Glass Pontoon construction technique - Joining sections

Discussion in 'Boat Design' started by Michael Hyder, Jun 30, 2020.

  1. Michael Hyder
    Joined: Jun 2020
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    Michael Hyder Junior Member

    Thank you, fallguy for your response. Yes, i Agree. Mr ondarvr had useful suggestions. Let me amend my previous post to note,the U-shape will be sealed by a fiberglass flat section across the top, the pontoons will be foam filled, and in alternating 4' sections i will put in 55 gallon plastic barrells foamed and secured then sealed in place. The laminate plan was as follows: pre built molded 4' sections/[ 1) Pre-built =gel coat-2oz matt-10 oz woven-2oz matt-10 oz woven Then, 2) join 4' sections with seams overlap 12" with 20z matt-10 oz -2 oz- 10 oz. Finally, 3) laminate entire pontoon lengthwise with 2 layers 10 oz matt-gelcoat 2 layers = 10 layers Total] My calculation was that two 33"X26' pontoons will have total buoyancy of 9,800 lbs. and total displacement of boat will be 4,000lbs max (equipment, crew, boat). Am i missing something?? Back to the main question. Mr. fallguy you indicated, "plan insufficient for a workboat,by a long way". Let me clarify, sir. Yes, it is a workboat, but its not a huge dredge operation. Medium duty at best. I have a small load of equipment, 50 hp motor and associated pumps , etc. Max total weight eq 2,000 lbs. Max crew 3 persons. Draft < 12-18". thats it... And i work close to port. 2 miles each way. Boat will be moored in Port daily. Removed beginning and end season only. That said, what would you suggest for a suitable laminate plan?? layers, etc. As an example, the cheapest Aluminum pontoons i can find and ship will cost in excess of 8,000$. the cost analysis i did for fiberglass is half the price. Your suggestions??? thanks again for your help, sir.
     
    Last edited: Jul 2, 2020
  2. Michael Hyder
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    Michael Hyder Junior Member

    Thank you Mr Effiiency, HDPE?? Forgive me, Im just a stupid Pilot and Newbie here. I thought HDPE is for pipes. I didnt know it can be molded into shapes, at least on a non-industrial do-it-yourselfer scale??!?!? I am open to any suggestion... So how can HDPE be used to make a sturdy pontoon??? It sounds like a great option. any direction is a good place to start. thank you again! ) UPDATE: After a few youtube videos I'm convinced HDPE is the way to go! I looked at HDPE pipe 24" Diameter, about 500 lbs for a 24' section, bouyancy 5000lbs! Which now leads this dumb pilot to the questions with regard to COST and ease of construction in field.. Can a guy with ZERO experience with HDPE do it in the field for a 10'X24' foot boat? Assuming a will ship two 24"D x 24' pipes. Welding cross members, end caps, front pointed pontoon ends, etc. I was looking online at HDPE pipe (SDR41, DN630) is this the type of HDPE I should be looking at? Do you know a good USA-based West coast supplier?
     
    Last edited: Jul 2, 2020
  3. Michael Hyder
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    Michael Hyder Junior Member

    KiethO. Yes, i agree a nice steel hull would be beautiful. In fact if I secure a good lease in a year or two, that is the idea. But for now my situation is low cost and a decent level of production. For this level of operation my 8" dredge is more than sufficient to get a couple hundred ounces in a season. Total weight of all equipment and crew not more than about 2,000 lbs. A 33"X26' pontoon sealed and built sturdy enough (this is what I am trying to determine) will have buoyancy of 10,000 lbs estimated. Draft < 12- 18".
    More than sufficient? Also, to clarify my initial posting, the pontoons will be sealed with a flat 1/2 " plywood/ Glassed top bolted down with rubber gasket. Pontoons will also be urethane foam filled, 55 gallon plastic barrels secured in alternating 4' sections and sealed in foam in case of water intrusion will have minimum 8 barrels for 4,000 lbs buoyancy total. Aluminum is out of the question for cost and welding (cant Al weld). Suggestions ? Can I build a strong enough pontoon in sections, then ship and join together in Nome. Lets assume i do what is required to build a strong pontoon . Can it be done? Laminate plan? thanks sir.
     
    Last edited: Jul 2, 2020
  4. gonzo
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    gonzo Senior Member

    I think you may be better off buying already made pontoons. For example, you can get aluminum pontoons at around the size you need for less than $900 each https://www.kendormarine.com/
    I suppose you won't care if they are a bit mis-matched.
     
  5. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    You laminate plan is basically the a little better than the glass plan of a canoe. The csm layers add nearly nothing but weight and the gc binder. 2 layers of woven is not good. I am a bit confused. You were going to pre-fab and then send these up and then assemble and post fab there? What is gained this way?

    You will have others here to advise a better glass plan than me.

    There are not 10 layers. You have 20 oz woven and 24 oz mat. It is not a good schedule and I'd say it will be a real pita to build that way. I do not have a lot of experience with mat, but I do know it offers little by way of strength v other options.
     
    Last edited: Jul 2, 2020
  6. KeithO
    Joined: Jul 2019
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    KeithO Senior Member

    Michael, if you want to know about steel pricing, visit www.myalro.com then click on "Metal products" on the menu, then follow the row "carbon steel" across to the right to the plate or sheet column. Usually plate is 3/16" or thicker. Sheet starts much thinner but comes up to a value over 3/16" at the top end.

    I took the liberty of just looking at a few example scenarios:
    in the plate section, I picked "Corten steel", 3/16" thick (thinnest on offer) and sheet sizes go up to 96" wide x240" long in a single sheet. This stuff is long enough to get many of the parts needed in a single length, especially any transverse features. I added 5 sheets of this to the cart and it came up with 6128lb @ $3627 thus $0.592/lb
    An alternate, since your barge is not going to be that big and you can put internal ribs all over it, I looked in the sheet section at 11ga Corten (0.12"). Those sheets are 48" wide x 120" long (so the width of the boat) and going with 20 sheets (same surface area as above but thinner) works out to 4000lb @ $1970 for a cost per lb of $0.492

    Any decent steel supplier would be able to take the plans from your NA and run them through their CNC plasma cutter to produce your entire boat in "flat pack" format and ship it to you on a few different pallets. At the build side, something like an excavator or backhoe would be a great help in moving material. For the size boat you are looking at, the steel supplier can plasma cut notches in the plates and tabs on the ribs so that everything is self locating and also allowing you to do (MOST) of the welds on the outside of the hull.

    I figure one would not normally use corten for a boat, but your boat is pretty small, so more sensitive to steel thickness and corten is stiffer than mild steel and has a higher corrosion resistance, which could be very helpful in your scenario since it is never going to have a perfect 2 part epoxy yacht finish... The usual way to paint things like this is to sandblast and paint with a zinc rich primer, followed by 2 coats of epoxy paint. One can paint as much of the inside of the hull with the zinc rich primer as possible before closing it in to help with the lifespan.

    The biggest consideration with the welding would be to keep things dry and clean, hydrogen embrittlement is a definite problem in such a cold climate, but you should be able to weld everything with one of the new mig welders with pulsed arc which produce great welds on thinner material without constant problems with cold welds from the older style welders. This is BTW the same technology used to weld aluminum, its just with aluminum everything from the welding source to the gun would be different because of difficulty feeding aluminum wire etc. But dont worry, aluminum would be well over 3x the price, just consider that once built you could leave it bare and never have to paint it. I dont know what that is worth to you, but paint is the bane of every seaman..... I dont know how problematic marine fouling is in Nome, that could require an ablative paint to keep growth off. But the big bonus is you already have divers so maintenance in the water may not be a big issue if you skipped it....

    If the barge concept is too much, then I would just raft up as many pontoons as fit under the deck (not just 2 or 3) and use aluminum I beams to connect them together transversely. Then weld more aluminum I beams between the transverse beams to complete the framing of the deck. Most pontoon style vessels that break up in the ocean do so because the deck structure was in no way rigid enough to withstand all the racking they are subject to. Finished pontoons from a factory are pretty cheap and cant fill with water based on how they are made. No need for filling them with foam, just properly add a bilge pump to each end so that you can pump out any water that gets in and are aware that there is a leak somewhere. There are some dry bilge systems that you can build that suck through a sponge and get pretty much every last drop of water out which would extend the life of your pontoons.
     
  7. Michael Hyder
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    Michael Hyder Junior Member

    Yes, the more I look at this your suggestion appears to be the best. Also, Mr efficiency suggest HDPE. I've been looking at that as well. For example, HDPE pipe 24" D x 24' runs about 450 lbs per Pontoon @ 5,000 lbs bouyancy per pontoon. HDPE welding seems a fairly strait forward process. Probably a lot easier than fiberglass.
     
  8. Michael Hyder
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    Michael Hyder Junior Member

    Mr. KiethO. You are an excellent example of why forums like this are extremely valuable sources of information. Professionals like you post information that can greatly assist business planning for people like me with limited technical expertise. I may know a lot about Gold dredging, but my knowledge of ship building is severly limited. Thank you for giving me some excellent ideas for future upgrades in my business!
     
  9. KeithO
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    KeithO Senior Member

    Disclaimer, Im not a NA, but ther are plenty on this forum who could handle the design. I'm just an engineer who knows a little about welding....
     
  10. bajansailor
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    bajansailor Marine Surveyor

    Re your buoyancy estimate, you appear to be including the full volume of the pipe (which I calculate to be approx 4,675 lbs in fresh water).
    For practical purposes and safety reasons you do not want to immerse your pipes more than halfway, hence that gives an effective buoyancy of approx 2,337 lb per pipe. And if you knock off the weight of the pipe then you are left with 1,887 lbs of buoyancy for your payload.

    I would agree with KeithO, that the best material for your gold dredge barge is most probably steel.

    Have a look at this recent thread - Darren wants to build a 24' steel barge for transporting a small excavator.
    Flat top barge https://www.boatdesign.net/threads/flat-top-barge.63920/
     
    Last edited: Jul 2, 2020
  11. Blueknarr
    Joined: Aug 2017
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    Blueknarr Senior Member

    Have you considered welding a bunch of steel 55gal drums end to end?

    The ridges will be a bit draggy, but there should be a cheap and ready source in Nome.
     
  12. KeithO
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    KeithO Senior Member

    Ignore this guy, kids all over drown trying to make a rafts out of metal 55 gal drums... Its not something you want to use in the arctic trying to make a profit...

     
  13. fallguy
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    fallguy Senior Member

    Your post is obtuse. Please explain things rather than suggesting ignore someone.
     
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  14. Blueknarr
    Joined: Aug 2017
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    Blueknarr Senior Member


    Thanks FG

    Were those death rafts designed, engineered and constructed by qualified adults or children who haven't finished highschool?

    All over of the world, multitudes of properly designed, engineered and constructed barges, pontoons, docks and other floating stuff utilize 55gal drums.

    It is ignorant designing, non-engineering and crappy construction which make a vessel unsafe.
     

  15. KeithO
    Joined: Jul 2019
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    KeithO Senior Member

    So welding together steel drums of unknown condition, which you found in Nome AK constitutes "designed and engineered " ?

    I have made some things out of drums in my life, all very benign compared to a dredging barge that is going to be operated offshore in Alaska in water that is close to freezing year round. The location has virtually no roads, everything comes in by boat, everyone has a 4 wheeler and a snow machine. Fuel drums are an in demand item for their original purpose and they dont even fulfill that very well if the examples of leaky drums spilling gasoline over miles and miles of frozen lake/rivers/ocean are anything to go by, and thats just what they show you on Discovery.

    There is some use of plastic barrels as flotation for floating docks and the like, but even with those one has to be very careful with which ones you choose and where the bungs are oriented. Securing them is not that simple since they are rather squishy. And the deck in that case is the only real structure with the barrels just for flotation. But I doubt the OP is going to find dozens of surplus plastic barrels in Nome, nor any usable steel ones and if they start out usable, they probably wont stay that way for long in the marine environment.

    The barrel stoves I have made for boiling maple syrup typically last a maximum of 2 seasons before they are rusted out, and that is just outdoor use with exposure to rain and ash, not any sort of salt environment. The steel that goes into them is probably less than 0.030" thick and really low grade.

    The OP is going to pay the claim owner a hefty fee for the privilege of looking for gold there with his dredge. Something more durable and that can survive multiple arctic winters ashore under a lot of snow and ice is going to be more conducive to his success. That probably precludes some of his original ideas. If he does use pontoons, he may have to add skids that are structurally attached to the deck to reduce the load on the pontoons when ashore or beaching in the winter or they may all get flattened at the bottom from the vessel weight + snow and ice load.

     
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