pontoon Idea! will it work???

howdy,
wanting to build a pontoon around 14ft (4267mm) in length and 6ft (1828mm) in width having 3 pontoons, i work with sheet metal all day everyday making air ducts so i figured that using .6 or .8 sheet metal rounded to 550mm dia would do the job along with EPS foam found here ( http://www.koolfoam.com.au/boat.htm ) to fill the pontoons for it buoyancy then fibreglass them , gell coat and do all the necessary steps in water proofing it,

the cross members would be wood and alloy and the deck will all be wood and i will not need all the nice chairs and furniture found on other pontoons best try to keep the weight down. its just a fishing boat to get around the rivers here in australia. and as for this EPS foam is says A cubic metre of EPS with a density of only 16 kg/M3 has a buoyancy of 984 kg!!!!!! really?????? lol

just would like to hear from some of you what you think about this Idea
will if float? will it sink what are your thoughts???? what else should i do

thanks guys
nick Australia

 

A cubic metre of water weighs 1000 kg, a cubic metre of foam weighs 16 kg, thus a cubic metre of foam will support (1000-16)=984 kg. This is if the foam is actually submerged. It's not doing a darn thing if it's inside the pontoons unless the pontoons are leaky.
Buoyancy in a pontoon boat comes from the fact that the watertight pontoons have a volume substantially larger than the volume of water which the boat must displace. So long as your pontoons are watertight and their total volume in cubic metres is greater than the weight of the loaded boat in tonnes, it should float. Whether it will float and perform well, is a far more complicated story.
Fibreglassing the outside of a metal hull is generally not such a good idea; it tends to just trap water against the metal and encourage rusting. Pick either glass or metal, not both. Waterproofing is achieved by a good welding or rivetting job in the original construction of the metal hull, no goo allowed.

 

The whole point of glassing is to get a shape that's ideal. The point of pontoons is simple constriction from round aluminum pipes to whick ends are attached. I would say that if going to the trouble of glassing, make a U shape because it has a flat top and so carries bouyancy more progressively as height increases, allowing better characteristics for rising after plunging.
The method of building potoon boats is entirely due to the limitations of cost of labor, like many consumer goods. You are not so limited. Your materials will cost the same no matter how you assemble them, so why copy a production process that is based on cheap untrained labor?
You could also make a U shape out of alloy. All that's needed are some inverted tombstone-shaped bulkheaeds. Seems you could first do bends and have a single standing seam along the top of the pontoons, wrapping around the bulkheads. Then that could be clamped and welded, and the standing seam could be cross-drilled to make an attachment point.
Good welding at the bow and stern and watertight bulkheads bow and stern will eliminate the need for foam. You always have the second or other two pontoons to float you if the first fills.
An inspection/pumping access cover would be good.
An alternative to all this would be large diameter PVC tubes with fiberglass bows.

Alan

 

to maintain flotability in case of leaking foam is a expensive solution - get PE bottles and put them inside...
Cheers Wil

 

thanks for your replys everyone there good, but still dont know if it will float so trial and error will it lol

alan white
due to the limitations of cost of labor, like many consumer goods. You are not so limited. Your materials will cost the same no matter how you assemble them, so why copy a production process that is based on cheap untrained labor????????????? what do you mean by that? i dont understand are you telling me to go buy one when in australia they cost thousand of dollars when i can build one with help from the people from this forum with a next to nothing cost!!! i dont understand

 

Not trial and error, yarrick, just some math. Building one, sinking it, building another will get very expensive very quickly. Calculate how much it'll weigh, then calculate how much volume you need to support that weight. We can't do the design for you, but we can walk you through the steps if you want us to.
Alan is telling you that most production boats are designed for ease of manufacturing in a factory with lots of workers; since you don't have to pay unskilled workers to build your pontoon boat, you should look instead at construction methods oriented for one-person building, and can afford the time to build a more suitable hull shape.

 

I believe he is telling you that if you are going to make it yourself...do a better job than the production boats. They all use round tubes...do yours in a U shape (cross section) and get a better performing boat. See the attached drawing.

 

Yes, as Marshmat says, factories build things to suit their limitations or advantages, and so should you. The methods themselves usually define the production in a factory. An example is the Coleman canoe, which has a hull designed to nest inside a hull inside a hull inside a hull an identical hull for shipping. You might say, "Hey! I love my Coleman canoe! I want to build one identical to it!"
Why? So you can nest 50 of them in a stack?

Alan

 

Thankyou. Exactly what I meant. As long as one can weld and shape metal, do something that works better than a machine-welder that just turns out pipe.

Excellent illustration!

 

Yarrick 88 G'day mate.

I too work for a sheet metal company but not a sheetmetal worker I design, build and maintain their materials handling equipment.

The first rule in designing something is: "Don't design it if you don't have to." well it's not really I just made that up. But it's the priciple I use. Or don't re-invent the wheel.

There are boat shows all around Australia and if they are like ours they will feature pontoons. Go and have a look at the them, check out the sizes and build one the same.

I don't know the capacity of your rolling machines but you should ba able to roll aluminium then you don't need the mess of fibreglassing.

Welding ali angle down the length will provide stability and where you bolt your framework for the decking. Treated pine might be OK for the decking with the handrails in ali as well.

Don't forget the most important part, storage place for the eskies, weight distribution is important as well. Make sure you distribute your eskies evenly around the pontoon with the added benifit that you wont have to walk far for a drink. If the bow starts to sink lower in the water, crawl up to the stern and consume piss from the other end to level it.

Nah only joking I don't believe in drinking while in control of a boat. That's why when I'm drinking I lose control.

Poida

 

hahah

ohhh mate lol i love it, for the eskies there weight will be nothing, there is this foam its called P3 ducting foam, there is an alloy coating over the foam its no thicker than paper, and it does not condensate. esky size 1190mmx590mm @ 650mm high the foam is 50mm thick! a basketball weighs more,

as for the planning i am looking at all shorts of shapes, round, hex, U and V,

about the roller its 3 meters long, we dont have a tig welder at work so will oxy weld do??

also i have been looking at those mini pontoons thinking that making one of them will be a good first for me but some of them are using .6 alloy i could throw a fuckin screw driver at it and it will make a hole lol, we all know its lighter then steel but i am gonna stick with steel, sounds more realistic
as for the desgin its on the drawing board At the moment and will be posting some photos pretty soon so you guys can have a good look and do some correcting

thanks alot everyone