Lake Titicaca and the Island of Sun, Isla Del Sol, is a rare vacation spot that beckons anyone who visits La Paz, as it did me and my friend Emily. The altitudes are well over 13,000 feet; the surface of the lake itself is already over 12,500 feet. To get there you take a 4-hour bus from La Paz to Copacabana on the Lake, with a stop in El Alto. From Copacabana you take a 2-hour boat ride to the island. Doing this was a little tricky for us, however. This is Bolivia, where nothing is totally clear. And so we crossed a body of water on bus on a barge.
You can catch a coach bus to Copacabana from the main depot in La Paz or from Cemetario, the secondary bus depot high up in an elevated district of the city. There are cable cars that bring you there if you’re commuting from the bottom realms of La Paz. By the way, going via overnight bus is not recommended as buses are known to be hijacked on country roads at night.
When we were close to Lake Titicaca, we stopped in a city called Tiquina situated on a wide strait. The locals got off the bus to take various small motorboats along the small marina. I assumed they were going to small ports along the water, closer to their destination. But no, they were zipping to the other bank awaiting our bus.
Emily and I, and a few other Spanish-speaking tourists stayed on the bus since we didn’t understand to disembark here. No, the driver did not check to tell us what’s happening — quite Bolivian. So we got to experience crossing the waters on a bus on a rickety barge.
Although the bus rocked a little and it was quite slower than driving across this length on a bridge, we arrived safely ashore to the other side. The coach drove a little longer, we walked half an hour through the Copacabana to the beach and caught a boat to Isla Del Sol.
Still curious afterwards, I did some reading on Archimedes’ Principle on buoyancy, made some calculations and learned why the Tequina barges were a reasonably effective and safe method of getting a busses and cars across the water. Archimedes’ Principle is a law of physics that declares in order for a boat to sink the pressure applied must exceed the pressure, or weight, of the water it would displace. Meaning for this barge to sink so that water reaches over the side to flow into the barge, it needs be heavier than the weight of the water it would displace.
These are my calculations:
The water in the strait is fresh water.
Fresh water weighs 8.34 pounds per gallon.
Cubic foot is 7.5 gallons.
A cubic foot of fresh water is 62.4 pounds.
If I estimate our barge at 4 feet high, 50 feet long and 12 feet wide.
That is 2400 cubic feet
or 149,760 pounds.
For it to lower enough so that the water is rushing into the sides of the barge, the barge would have to press into the water at over 149,760 pounds, which is that weight in fresh water for that size.
I researched weights of coach busses and ones on the heavier side is 30,000 pounds, so lets assume our bus was 30,000 pounds. If the barge weight just as much, also over estimating the weight, together it would total 60,000 pounds. Add that to weight of passengers who stayed on the bus and the various people working to get the bus over, plus everyone’s luggage it would still only be 6,000 pounds.
The total pressure applied to the water, 66,000 pounds, would only push into the water 1.75 feet. Meaning only 1 ¾ foot of the bottom of the barge is in water, safely allowing barge, bus and all to float across.
On our way back however, we decided to skip the barge ride and do as everyone else, which is pay the 2 or 3 Bolivianos (about 40 cents US) to ride the small ferry across. One bus-barge ride was enough.
