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PVC catamaran Answered

So I was thinking of building a catamaran out of two pieces of PVC pipe, either 6 inch or 8 inch. I don't know how long it would have to be to support me or maybe others. Does anyone know of a buoyancy calculator I could use to try to figure this out? Or maybe I could use ABS plastic. This is very easy to heat and bend. This way I could actually shape it a little more, instead of having it just be round and less controllable.


I sent money to Marjamada for the dvd for rebelcat5 and he hasn't responded to my order or even ackowledged my payment. Apparantly this site of his is a hoax and should not be taken seriously. I have sent two requests to him for acknowledgement and have received nada, nothing. So far, I am out the money I sent him but there are ways of payback for such criminal behavior as this.


7 years ago

where would you buy pvc me and my dad plan on making one

http://rebelcat.com/Flotation-Chart.html DO NOT USE ABS PLASTIC! It is soft in the middle betweeen the inner and outer walls.

To calculate the bouyancy, simply find the volume of the PVC pipe. The weight of the water that can fit in that volume will be how bouyant it is

I'm pleased to find a discussion of one of my favorite topics - PVC pipe catamarans. I have made three and now have considerable experience with them, up to 20' and 15" diamater (RebelCat.com, Cat 4). My site has plenty of techniques and materials to check out. I wish someone had pioneered this when I was stumbling around. On the other hand, I like sharing what I've learned.

Hi Marjamada.

Nice Catamarans! Your website has a lot of pictures.
I have a project for a PVC Proa (an Oceanic Outriger).
I made a model at 1:5 scale.
You can see pictures at:
The original idea is from Othmar Karschulin, but he didn't build one yet.
I want to know why you change from bolted to tie ratched pontoons?
What you think about what Toxonix says "Also, PVC becomes unstable when heated enough to re-liquefy the monomer matrix. Its plasticity is reduced, making it more likely to crack and fail. "?
In my design I cut the pontoons and use epoxi to make the shape. But I don't know if this is a better solution.
(sorry about my English I'm from Argentina)

Gracias, Andre, I'm glad you like my work. The reason I no longer bolt the frame and deck to the PVC pipes is because this is PIP thinwall, the thinnest pipe available, for lightness. It is difficult to get a good connection by bolting to such thin (weak) pipe walls. Also, I found that straps give a better flexible joint, because the pontoons move independently - fixed joints will break if they don't allow movement. The heated and shaped parts of my RebelCat 4 are extremely strong, but I did not "re-liquefy" the PVC, only softened it enough to shape it. Epoxy is okay for small pipe like you used, but do you know how much epoxy is needed to fill a 15" pipe? Also, epoxy is heavy and expensive. My shaped PVC pontoons are strong and light. Alternatives are traffic cones and megaphones.

I thinking use a thin layer of epoxi over plywood, not to fill all the 15" pipe. But I will try your technique in furder tests. Thanks for your advise and recommendations. I like your RebelCat4 with that wedge shape. Are you not afraid that the pontoons rotate in its own axis?

if your thinking of useing plywood, I would look into "stitch and glue" boat building.

Andre, yes the pontoons do tend to rotate, but very little. This is easily corrected by cementing curved strips of the same pipe material on the pontoons next to the feet to prevent rotation. Believe me, the pontoons move up and down when they encounter waves, and they meet waves at different times. So the joints where the deck/frame meet the pontoons must 'flex'. RebelCat 2 had the frame bolted to the pontoons, and that was a serious mistake. Remember, these cats are made to be taken apart and carried on top of a car or in a pickup, so the joints - where things connect to other things - cannot tolerate the strain like cats made from much stronger and heavier materials. They are made for the ocean, mine are for calmer lakes. Two very different worlds. -Martin rebelcat.com

Marjamada, please post RebelCat 5 as an Instructable - it looks like a wonderful project.

(you will then need to post an 'ible on How to Sail...)

Kiteman, thank you for the request, however... the project is complex and therefore will be presented as a DVD video, with printable 'blueprints' of the parts and a step-by-step instruction on its construction and assembly, as well as sailing. Brief coverage will, of course, be on my web site, as are the other cats. The DVD will be available from the site. RebelCat 6 will be the re-designed RebelCat 1 - the prototype I made in Brazil. It will appeal to kids and solo sailors, and it will be the one you can carry on a trailer behind your bicycle. -Martin rebelcat.com

Hey, thanks for sharing! I missed this the first time you posted - but I really love your PVC catamarans :)

Could you use a design like this to make the ama's. (i think that's the right word)

Just a thought. It would be light and could be bigger.

Hi! I am trying to build a catamaran styled car/boat off of a volkswagon chassis. Does anybody know the density of fiberglass versus water and if I were to fill the empty voids full of foam what kind should I use? Thanks

ROFL, ok so I can't offer anything constructive here, this just made me laugh

Buoyancy is all about displaced volume - each litre of (fresh) water displaced will support a kilo of mass.

Calculate the volume of your pipes (Pi x radius-squared x length), covert to kilos, subtract mass of pipes, that's how much extra they will support.

e.g a 3m (10 foot) length of 20cm (8 inch) pipe will only support a little less than 9.5 kilos, including the mass of the pipe itself.

Since you probably mass around 70-80kg, you will need about 20-25 metres of pipe just to hold your mass, never mind the mass of the rest of the boat (deck, masts, decorative flag). You should consider a different way of displacing the water - "pipes" made of barrels bolted end-to-end?

Kiteman, you are correct about a litre supporting a kilo, but incorrect about how much weight a 3m by 20cm PVC pipe will support. I think you misplaced the dot - it should be close to 95 kilos, not 9.5. I made such a catamaran from this size: 6m PVC (check RebelCat.com) and it worked great.

Damnable math is always getting me too.

hmm just checking, so say i want to support 400kg i would need to have 400 litres of air in the water (in the form of pvc tubing), soo if 1m3 = 1000litres, then 0.4m3 = 400litres, yes?

Drummer ian, that's right. I have a chart I made for different diameter PVC pipe and the amount of displacement for each. The formula I use is pi x diameter squared divided by 4 (same as pi x r squared) to get the area of the circle (the end of the pipe in sq cm. Multiply that by 100 (cm in 1 m) and divide by 1000 (cubic cm in one L)(or just divide by 10) to find the number of litres in one metre of pipe. My first cat was made from 6m 20cm thinwall PVC pipe which had about 188 litres total bouyancy and I now consider the MINimum for a boat for one adult. You want to have HALF of your bouyancy above water, so the total load - boat, crew, gear - must not be more than half your total bouyancy. Martin rebelcat.com

awsom thanks, im thinking of building a bike powered cat to enter in a raft race, i live in the UK and have no idea where to find 20cm diameter pvc pipe, and, even if i do manage to i expect it will be astronomical prices!

Drummer ian, sounds like a great project. PIP (thinwall) PVC pipe should do fine. It's easily available at commercial plumbing supply - the ones that have sewer and drain pipe - in large outdoor yards. Get the PIP and it won't be too costly. Prepare for the pickup - take a saw and measuring tape. Plan to cut off the 'bell' end (widened to accept another pipe), and THEN measure to find the halfway mark. Be sure to get 4 caps if you plan to close the pipe that way, and PVC cement.

does pip cost less than pvc sense it uses thinner products?

Why bother making all those wheels you could have one where the bike is suspended above and the rear frame is widened to accept a paddle wheel, or you could get a propeller and run that, even a big water screw, I think water screws are better than props at low rpm so would be good for a bike boat but check that with someone...

Yes. Don't forget the weight of the pipe itself, though.

Hey has anyone made a submersible out of pvc yet?

ABS is safer, less brittle. Also, PVC becomes unstable when heated enough to re-liquefy the monomer matrix. Its plasticity is reduced, making it more likely to crack and fail. ABS and other non-vinyl plastics don't burn off their plasticizing elements when heated. Personally, I'd use plywood to make a multi-hull. I hates PVC.


10 years ago

I would love to build a catamaran too some day and the abs plastic your talking about, how big of sheets can you get i'm just now looking into it. It sounds like a very good material to use as a skin for the hull. Correct me if i'm wrong or even add to this but could you make a pvc frame and then use the abs plastic sheet to mold around it?

zmatt, it's also possible to heat and shape PVC pipe. Plumbers do it all the time. Heating and shaping a large pipe is not easy, but I think I was the first to do this and you can see the results at my site RebelCat.com. I heated 15" PIP PVC - that's thinwall - and I really should have had six people to help when it got hot, instead of only one friend. It is possible to create a wedge at the front, just like modern cats and tris. I will soon have a video on DVD about this technique at my site.

In one of the "Make" issues it shows you how easily ABS plastic can be bent. And how much it retains its shape. I don't think you would have to pvc as a frame at all, this thought has crossed my mind as well. I think it would be just fine if you heated the abs plastic and bent it. As for the sizes. I'm not too sure on this. Best bet is to call Lowes or Home Depot.