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Bruce’s Pontoons

We were planning to use Bruce’s pontoon boat that he scored somewhere
around the Lake Shasta area as the base for our shantyboat.  In fact, it
was Bruce’s pontoon boat score that gave us the greenlight for this
project.  Not so sure about this now.  Every boat has a buoyancy, a
certain weight that it can support safely.  Bruce writes:

I don’t know how easy it is to calculate this. During high
school geometry I had a crush on the Castellucio twin sisters (Karyn and
Kathleen) and most of my mental energies were taken up by trying to
flirt with the two of them rather than on the substance of the
coursework. I haven’t really revisited the subject of geometry (nor,
alas, the Castellucios) since that time.

The pontoons
are sort of irregular shaped, they are flat on the top and sort of
u-shaped on the bottom. The top to bottom dimension is 17 1/2″. They are
18 1/2″ wide.  As I’ve mentioned before, the platform is 16′ long. The
pontoons extend another 18″ to the rear of the platform. They also
extend about 24″ to the front of the platform. However, in the front
they are tapering down to be much more narrow, expecially in that last
foot.

Okay, I’m
gonna make some assumptions about Bruce’s pontoon boat.  Doing some
crazy math that requires me to get out my geometry book again, I
guesstimate the total cross-sectional area of the pontoon is about 2 sq
ft.  To get the volume, we multiply that times the length. We’ll say
that is 16 feet + another 1.5 ft at the back, and another maybe 1 foot
at the front. For 18.5 feet. So the volume of one pontoon is perhaps 37
cu ft.

We just look at one pontoon, because we want to make sure
that the capacity we work with never exceeds the floatation of one
pontoon, lest a shift in weight drive it under the water and flip the
craft. This situation even has an ominous-sounding name:  Pontoon Effect.  Plus, if you think about two pontoons, you want them both no more than half in the water.

To
get the floatation, we multiply the volume times the weight of the same
amount of water. Thanks, Archimedes.  One cu ft of fresh water weighs
62.4 lbs. So the flotation of one pontoon is 37 cu ft  * 62.4 lbs/cu ft =
2308 lbs. So the weight of the boat, plus the passengers, plus their
gear and stuff, plus some margin of safety 10 to 25% should not exceed
2308 lbs.

Probably too tiny for our heavy shantyboat. However, we
can build Bruce’s pontoon out to be a little hillbilly sun porch to
accompany our shantyboat.  Something like this…

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