calculatewinners("|-----------~~~----------p~~~~~~|\n
                  |-------------------p-----------|\n
                  |------p----------~-------------|\n
                  |---------------~------p--------|\n
                  |------------p-~~~~~~-----------|", 
                  ["Adam", "Brain", "Flipper", "Franko", "Darwin"]) 
                  --> "GOLD: Franko, SILVER: Brain, BRONZE: Adam"

The test is ok:

Waves (~) take twice as long to swim through as smooth water (-).

It takes Adam 12 time units to reach the finish line, and for Brain only 11.