buoyancy) is critical in the design phase of your cat,
so pay attention.
There are four sizes
of PVC pipe that will work for a RebelCat
8" - 21.75 lbs /
10" - 34 lbs / foot
12" - 49
lbs / foot
15" - 76.5 lbs /
With two pontoons, each 10 feet long (total 20
feet of pipe):
8" x 20' = 435 lbs
10" x 20' = 680 lbs
12" x 20' = 979 lbs
15" x 20' = 1530 lbs
How to Use These
the weights of your boat, crew and cargo, then
double it - that is the flotation you
need. Why? Because you must have at least HALF of your
total flotation out of the water.
Let's Try to Calculate
Our Flotation and Pipe Length:
Boat Weight (RebelCat 5): approx 250 lbs
Crew Weight (two adults 150 lbs each) = 300 lbs
Cargo (camping gear, food, water) = 50 lbs
Total Weight = 600
Flotation Required: 1200 lbs (600 lbs
How do we create 1200 lbs
flotation? We select a pipe diameter and
10" diameter x 18' (x 2) = 1224 lbs flotation
(34 lbs/ft x 18' x 2 pontoons)
12" diameter x 13' (x 2) = 1274 lbs flotation (49 lbs/ft x 13'
x 2 pontoons
Why Do I Have to Calculate Flotation?
Doesn't the DVD tell me that?
No, because a RebelCat 5 can be made using
PVC pipe 10" or 12" in diameter and in any length. Also, you
have to decide your total weight, based on boat, crew and
1. Build your cat with extra flotation. It is far
better to have too much than too little. You might want to have
a guest on board or carry more cargo. You may have to rescue
someone. Strong wind will always try to push your leeward
pontoon under water. In flotation, more is better.
2. Make your cat longer than
10' (not counting cones). The longer your pontoons,
the more gentle your ride. Short boats have to go up and down
over each chop and wave. Longer pontoons can ride on two or
three chop waves at a time, keeping the boat almost level. If
you like rodeo rides, go with short.
My RebelCat 5 is 10" pipe, 21'
long, including cones aft. It rides like a Cadillac.
(see video on the Home Page) Sure, it
turns slower than a short cat, but I'm not usually in a hurry
to turn on a dime. Your call.
If I were to make another RebelCat
5, I would use 12" pipe at about 17' long. That would
give me plenty of flotation for three to four people and enough
length for a gentle ride. The reason I used 10" pipe was
because I could not find traffic cones 12" in diameter
(someone has since informed me that the Home Depot in his city
has them that large), and I wanted to use materials that most
peopel could buy locally. So I made my RebelCat 5 as a demo for
My next RebelCat 5 would be made from
12" pipe, and I would either locate those 12" traffic
cones or I would heat-shape the aft end of the pontoons
(similar to RebelCat 4 - see RebelCat Evolution here). Traffic cones may appear
unprofessional or unusual, but the fact is they perform better
than anything I have tried. They allow the water behind the cat
to close with very little turbulence or wake, which means that
little of the sails power is transformed into swirling water
(which required energy). The video of
RebelCat 5 sailing fast on the home page demonstrates how well
traffic cones work.