Material choice for twin hull barge/work pontoon

So I am thinking about a pontoon/barge to transport building materials like wood and concrete to an island.

It won't be used in heavy seas, if it's too windy it won't be used. Distance from shore is 8km, in an archipelago.

I'm thinking about a couple pontoons about 500mm in diameter, square or round. At least 6 meters long. Targeting a floatation capacity of 2000kg.

Ideally would be able to land on to a rocky beach without extensive damage.

So my question is, what material would you recommend for building such a vessel, from the pontoons up?

Cost is always a factor of course.

Wood is easiest to work with, but how will it last as a pontoon? Aluminium would be great but expensive. Steel is easier than aluminium, but at the cost of less floatation capacity. Fiberglass has many resources available, but seems like it needs the most labour to manufacture. Plastic? Also surprisingly expensive for the mission I have.

Any advice or other points that I have missed here are appreciated.

 

Polyethylene pipes (MDPE) are extremely tough as long as the supporting/connecting structure is correctly built.

 

Would you know of a good source for this material? I see HDPE pontoons but they are pretty expensive locally at least. MDPE I haven't seen yet

 

There was a gentleman on here a few years ago looking to build a pontoon for transporting a 3 tonne Komatsu excavator to work sites on different islands.
I sketched a very basic proposal for him for a 22' x 10' steel catamaran barge - this can easily transport 3 tonnes,
I will attach a couple of sketches - could something like this be suitable?
Here is a link to Darren's thread - in the end he built a 'composite' barge with standard dock floats for buoyancy, a timber deck, and a steel framework to join everything together.
Flat top barge https://www.boatdesign.net/threads/flat-top-barge.63920/

 

I mean yeah that is pretty much what I want

 

Just to confirm, do you want a steel barge similar to my sketch, or a barge with standard plastic dock floats, similar to Darren's barge?

 

Ah yes. I definitely want a steel barge, however I can probably afford a plastic barge with steel frame. I haven't done BOM cost calculations yet.

 

I think that you should be able to send a message to other members once you have about 5 posts on the Forum (is this correct @Boat Design Net Moderator ?) - once you can send / receive messages you could send me your email address, and I will send you some additional sketches re the steel barge in the sketches above (if you think it might be suitable for your purpose).

It will be interesting to see how your cost calculations compare for an all steel barge vs a plastic barge with a steel frame.

 

There are many ways to skin a cat, and for this SOR I would go in a different direction. Search locally for a used motorboat, 7-9m long, something with a shallow V bottom, non-functional engine and a little neglected. Shouldn't be hard to find some old cabin cruiser that had big engines and became expensive to run. The transformation is easy, chainsaw the superstructure away and reinforce the opening with angle iron. Remove the engines, double the transom with a sheet of thick plywood, attach an outboard. The forward part of the bottom gets a sheet of 2mm steel nailed over it, and your barge is ready. If the thing is wood and you are concerned, treat her with some CSM and polyester on the outside and a few cans of PU foam on the inside.

 

You appear to want a very robust utilitarian hull with a job to do where cost is more important than appearance. A practical purpose built machine to get the job done. That makes your job easier. You also have something called the EU, which has rules about flotation that may make the job more difficult. I could be wrong.

Are you transporting materials for one building, or for longer term transportation of materials for many buildings?

If you are building one building that will be insulated with extruded polystyrene (XPS) panels, and the barge will not be used later, perhaps a simple scow built around the insulation panels for the building would suffice. If your building codes require as much insulation as they do where I live, you would need a lot of foam. A scow could be screwed together using standard size construction grade lumber that can be recycled as the last load of material for the building. Rust takes time, so any fastener will last long enough. Leaks are no problem. If you don't have to drag it over rocks, you don't even need a bottom since the foam will suffice. It could be towed with a rented boat. Hydrodynamics require either good design or low speed. 8 km makes low speed an option. This temporary shipping crate/barge eliminates any difficulties associated with disposing of the inexpensive derelict vessel suggested above, but has its own set of problems to be sure.

A decent steel barge may have high enough resale value to make it a viable option. A local boat yard looking for a new work boat in the near future might be interested if you could tailor the design to their needs. You could both save some money.

If the ultimate need is for a boat that you can use to get to the building once it has been built, that would make a more sophisticated boat a better choice. I would consider the shallow draft advantage of a garvey over the apparent simplicity of a pontoon boat. Spira designs had a nice platform boat, but they have gone out of business. Someone here might have the plans for the Matagorda, 7.3 x 2.5 m, 500 kg hull, 1100kg displacement, which is less than you want, but 7 meters is 7 meters, and pontoons have no buoyancy between the hulls. I have a screenshot of the study plans which are nearly enough to build from if you have some boat building experience. Any good NA would probably disagree with me about that.

 

That sounds great. I love me some sketches and cost calcs

That's also an interesting route, depending on what is available of course. Hadn't thought of CSM on the outside of a wooden boat. Our tar traditions are strong so nothing else has crossed my mind before to put on a wooden boat.

Yes, utilitarian is the word. Just one building for now. As far as towable barges go, there is no regulation. If it has a motor over 20hp or over 5.5 meters LOA you do have to register it, but that is not too hard. It needs to have a 50cm x 75cm space for each passenger you want to register and then the regular safety equipment like fire extinguisher etc.

There will be insulation needed for the building, mainly to stop ground frost coming up the foundations. So it might be an option. This made me think, is XPS a viable core material for a more permanent vessel? I am planning a concrete pontoon dock, with EPS or XPS core, but maybe it can work for a work vessel also. Not with concrete though.

I have been thinking that maybe I can do with 1-1.5 ton displacement, if the other benefits of the vessel make it so. Realistically 1000kg is the most I would want to put on there at once + a couple passengers.

I would also be interested in any drawings you have. Never hurts to learn IMO.

I'll bust out excel for some calculating.

Thank you all for fresh ideas that I hadn't thought about!

 

I wouldn't normally advise someone to put CSM and polyester over a wooden boat, but it's a cheap way to waterproof one. Sure the wood will eventually rot away, but if it buys you 10 years out of a tired hull it's fine. Just don't put it over something that's truly rotten, it must still have reasonable strength. If you really like the design you can use the old wooden boat as a mold and build a fiberglass one around it, in that case it doesn't matter how rotten it is, but that's more expensive.

XPS isn't a viable core for what you want, you would have to put enough fiberglass over it to make the foam redundant, and it needs epoxy or a special polyester that's nearly the same price.

For a start at plans you can look if you find something suitable in the FAO database, FAO Fisheries & Aquaculture https://www.fao.org/fishery/en/vesseldesign/search?page=1#search

The cheapest way is to repurpose something existing. Finding something local is often a question of asking around, the kind of boat you need isn't often advertised nationwide. There are of course exceptions, for example this beauty is advertised for 600€ and the superstructure will provide enough steel to make all the repairs needed and overplate the bow to ice standards. Sand blasting and painting will cost more then the initial price, but properly chopped and in good repair it's actually going to have some value. Omavalmiste teräsvene | Myydään | Tori Autot | Tori https://autot.tori.fi/veneet/myydaan/moottoriveneet/118107144
Another one, this time glassed wood, 1000€ (yes I know, making it into a workboat is blasphemy). Projektivene | Myydään | Tori Autot | Tori https://autot.tori.fi/veneet/myydaan/moottoriveneet/114507853
I'm avare they're most likely not local to you and transporting would be to expensive, so I'm just using them as examples. Cut the profile of the wooden boat into the steel one, or cut below the window line on the wood one to transform them into workboats.

 

I was looking at that steel hull also haha! If it wasn't for expensive transportation, it would be worth buying it for the scrap value alone.

As far as the wooden boats, I have to be honest I feel the need to restore them when I see one, not cut them up

And thanks for the link to that database!

 

Under 5.5 m LOA? Any restriction on beam, say 11 m? :>)

WPS and EPS are a POS as far as core materials are concerned. Around 1970 when National Fisherman was still a newspaper style magazine, they concocted a test for core materials. Build a simple boat, throw it off the wharf, look for delamination. XPS and EPS delaminated badly. If you do want to glue the stuff, Foam Fusion is best adhesive. The foaming polyurethanes are good if used sparingly and clamped snugly. Loosely clamped PU joints are all air bubble and have the same shear strength as air. Thickening with fumed silica and wood flour that can reduce the foaming, probably because by the time you mix them in half the gas has been generated already and kneaded out. Still working on it. I digress. You can bend it if you attach a layer of glass or paper to the outside of the bend.. This is the only example I have seen where foam is bent this way (at 3 minutes) and the video makes no mention of it. The rest is fun, but off topic.

Excel? As a sketchpad? Makes nice graph paper but the sketches are rough. I was toying with a platform boat idea once. I have no idea anymore what some of the sketches are, but the Matagorda study plan is there. I did help build a 7m plywood pontoon boat from an artist's sketches once. We totally winged the whole thing. Where the panels transition from the curves at the bow to the straight run, they want to bulge outward if the plans are nothing but a rough sketch and you have too many frames. Further proof that a plan done by a competent designer is needed. The guy had money, no clue and wanted his boat, so we sorted it out on the fly. Could have gone more smoothly.

 

Hmm... I cannot find a beam restriction anywhere, so technically yes that is possible

Definitely, that guy has some interesting content.

Thanks for the file. I definitely don't have an excess of money, so I must take the route of excessive analysis.