DIY Homemade Catamaran Sailboat from PVC pipe

RebelCat 4 - Inspired by Waterworld

Back from Illinois, I started designing RebelCat 4. It would be much closer to the original I had made in Brazil, but improved in many ways - more flotation, more sail area, kick-up rudder and centerboard like RebelCat 2, traveler for adjusting the boom's angle to the boat and for keeping the sail flat, adjustable fairleads for the jib... I had it all planned out and designed on my computer. So I got some 10-inch PVC pipe adn traffic cones.

10-inch PVC pipe

Larger pipe would solve the flotations problem of RebelCat 1, without making the cat longer. Well, cones on the rear would add about 30 inches, but that was necessary to close the water behind the hulls. I found some aluminum pipe at a salvage yard - it was perfect. Two sections 10 feet each by 1.75".

Cleaning used aluminum pipe for the mast

This pipe would make a perfect mast. 20 feet would be too tall, so I would cut one shorter. I cleaned it up with a sanding disc. I then made a coupler from slightly smaller steel pipe to join the two sections. All was going well. And then I saw the movie 'Waterworld', with Kevin Kostner and his 60-foot trimaran. I watched it again, and a third time. Hmmm, I began to wonder if this small cat I was now making would be big enough to make an impression.

What happened next is hard to remember, but I decided to make a larger cat. I found a perfect location on a farm outside town, bought some 15-inch pipes 20 feet long, and set my tiny 10-inch pipes aside for now.

Designing the seats outboard

I wondered how I was going to get this cat on my roof-rack, but now I was committed - no turning back. To see just how much bigger this cat is than the one I had started, look at the lower right - the 10-inch pipe is to the right of a 4-inch piece and is dwarfed by the new ones.

I'm sitting outboard where I want the seats to be, to give extra leverage without hiking out. The deck would be a completely new design as well.

Cutting foam discs for inside the pipes

This time I would not stuff the entire pontoons with foam, as with RebelCat 2. I decided that bulkheads would be a better way to use it. Two or three discs together, then a gap of 10 inches, then more discs. This would give rigidity with less foam, and it would create many bulkheads for safety. The discs have to be compressed to get them in, so they press from the inside.

Stuffing discs of foam into pipes with a tamper

A tamper/stuffer made from a mast section (aluminum pipe) and some wood scraps. After compressing a disc into the opening, the tamper is used to push it to its predetermined position. By marking inches on the tamper, starting at the head, it is possible to position a disc precisely. This is necessary to get the disc groups under load-bearing spots.

Making the form for heat-shaping the bows

This is the first stages of making the foam form which will be placed inside the nose of the pontoon so that the PVC will have something to collapse around when it is heated and folded to make the wedge shape.

This pic shows one side, with a single rectangle of foam as the center. Each side of the form was then filled with foam and covered with cardboard until it took on the shape desired for the nose. Had I known how stiff it must be to resist the pressure of shaping the hot PVC over it, I would have made it even denser and more rigid. RebelCat 5 uses an even more advanced method - no form remains inside at all.

 Cutting pipe prior to heat-shaping

Each pipe was cut back from the opening on opposite sides. The poontoon in the background has already been cut and the form is inside.

Foam form inside pipe prior to heat-shaping

The completed form is jammed into the pipe against discs which have been precisely positioned inside.

The task now is to heat the entire front of the pipe until it's soft enough to fold around the form.

One of the many challenges faced during this procedure was keeping the form from moving inside the pipe once the PVC became soft and no longer held the form in place. That's right, and I didn't think about it either until the form began rotating. It must remain perpendicular to a line drawn between the cuts, otherwise the nose will not form properly around the form. This and all of the other challenges of heat-shaping are covered in the DVD on RebelCat 5. No form remained inside on RebelCat 5, due to an advanced technique.

I did a lot of research on shaping PVC, but I found nothing about shaping large pipes into the kind of wedge-shaped, wave-piercing bows found on modern cats and tris. So I invented the technique. It worked so well, that I have advanced the technique on RebelCat 5. The DVD covers heat-shaping in great detail, and I believe I am the only one in the world to be doing this - creating hydrodynamic hulls from PVC pipe by heat-shaping.

Clamping the nose of heated pipe to shape it

A lot has appened since the last pic, but a friend and I were so busy with the heating, folding and shaping, there was no way to take a pic.

Briefly, the end of the pipe must be heated evenly, which means turning it like on a spit over a ceramic kiln where two large propane burners are blasting flame in our faces. It was so hot doing this, it gave new meaning to "slaving over a hot stove", hence no shirt.

The two by fours are attached by a hinge to form a crimper to seal the nose into a flat seam which was later glued, covered with a folded strip of hot PVC and glued again.

Pontoon after heat-shaping, pointed bow

By repeatedly heating small areas of the overlapping and somewhat wrinkled PVC, it was possible to iron out most of the bumps.

The front seam was then covered with thin, hot PVC and glued in place, feathered and sanded. The result was a wedge shape just like catamarans today, especially the larger ones.

It is now possible to make respectable and quite hydrodynamic pontoons from PVC pipe of any size. The DVD shows how.

Sanding heat-shaped hull

There were slight imperfections - bumps and dips - that I wanted to remove, even though they would not have been in the water. The 'curse' of the perfectionist, I admit. So I heated thin 'patches' of PVC to cover these areas and formed them over sand which I had used to fill the dips. After the patch cooled, I removed the sand and glued the patch in place. Here I'm sanding the edges of one such patch to blend it with the rest of the hull. Because the 'patching' process involved hot PVC, it was not possible to photograph it easily, but it was well-documented on video. I may have invented that technique also.

Notice the grey PVC strip which was heated and then folded and glued over the trimmed leading edge. I wanted a closed and solid nose, and this worked perfectly.

Paintin pontoon through templates

I made templates from clear, flexible vinyl from the fabric store, then taped them to the pontoons and sprayed paint over them. The paint is Krylon Fusion and bonds well to PVC, so well that when it dries it can't be scraped off with your fingernials. It's also specifically made for PVC and plastic. It dries leaving no smell after about a week.

TRansferring drawn design from pontoon to template

Since I had already created the design in the computer, I simply scaled it up from my computer printout to the templates. The parts to be colored were then cut out and sprayed through.

Template being removed from tail after painting

The tail of the pontoon was shaped in the same way as the nose, except that it was done horizontally. I wanted a 'tail', not a second nose. Also, the water on modern cats and tris is allowed to rise under the pontoon until it reaches the tail, causing very little energy-robbing wake. My design works in the same way.

 Pontoon fully painted

The first (male) pontoon is finished, the other lies waiting.

Screenshot of RC4

This is a screenshot of the design in PageMaker. I usually design in PM before starting construction. There are another 10 pages of technical drawings, showing the frame, seats, pontoons, and all controls, but they would take up a lot of space here.

I had intended to paint the sails as shown, but there wasn't enough time before the sailing event for which I was preparing.

Begin making mainsail on large tarp

The mainsail is huge. I spread out a 10 by 20 foot tarp to work on (it wasn't long enough, so I added plywood at the top), and using a chalkline, snapped a grid with 12-inch squares so I always knew where I was. My computer printout had exact coordinates for each corner, batten, reefpoint and cringle, so I simply transferred them to the grid.

Okay, simply is not entirely correct. It was more complicated than that, but as the cat will not move without a sail, I was determined to make this sail.

What made it challenging was the material. It was probably polyester, but it was also quite limp, unlike the Dacron sailcloth I used for RebelCat2. This stuff moved all over the place, created wrinkles, stretched, and generally made my life, um, exciting.

Sewing trampolines from colored polyester fabric

The sewing had only begun when the two large sails were done. I now had a pile of trampolines to make, each one having up to three layers.

I burned up my mother's old Brother sewing machine (shown here) and switched to my other machine, a White heavy duty portable. Three days later I emerged from my little cabin with an armload of trampolines, enough to carpet my room.

Begin assembly of parts into a cat

The two pontoons are first positioned on spacers I have made for the purpose of assembly. I don't want the pontoons rolling off someplace, and I want them to sit at precisely the same distance apart as they will be when attached to the rest of the boat.

Here I'm setting the back spreader on. It gives rigidity to the back of the cat and also holds the rudder. The pontoons are held to the spreaders and deck frame with eight ratchet tiedowns.

Notice the shape of the pontoons at the nose. They are quite close to the shape of modern cats and tris, which slice through the water and waves with greater efficiency than a monohull, which has to push a lot of water out of the way. These hulls have been heat-shaped.

Assembled on Lake Powell, Utah

Finally assembled for the first time on Lake Powell, UT, as part of a messabout of homemade boatbuilders. It doesn't look so big in this photo, but those pontoons are 19 feet long and weigh 100 pounds each.

RebelCat 4 at Lake Powell and me

Now you can see how big this cat is, with me standing next to it. I'm confident it will carry six adults. The trampoline on the back sleeps two comfortably. Can you believe I carried this cat on my roof-rack? To see my writeup of this event at Lake Powell, there is a page at with photos here.

So how did it sail? Like the wind! This cat is by far the fastest I have made, and sailing alone I was not able to sail it as efficiently as two. There are two sails to control at all times, the tiller (rudder) and the daggerboard. But I managed.

There are also two other controls for each sail. The mainsail has a traveller at the back to adjust the position of the boom relative to the centerline of the boat. The jib (foresail) has a similar control on the front spreader. The jibsheet blocks can be positioned at five spots on each side of the bowsprit, giving the crew better control over the angle of the jib in varrying wind conditions.

This cat is also the most complex and advanced of all the cats I have made. RebelCat 5 borrows heavily from the design and advanced controls but is much easier to make, because it is mostly wood. RebelCat 4 was the experimental cat I needed to make so that RebelCat 5 would benefit.

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