Michael Christensen- Modern Seamanship

For this book post I went into the library and picked up the first book that caught my eye (this one had white, bold, curvy letters against a blue background on the spine). Next I opened to book to the last three numbers in this blog's blog id and read that page in order to obtain a topic. I am sorry to report that the topic is about measuring the progress of a vessel.
Apparently the way to do it in 1972 was by electromagnetic log. A device is attached to the bottom of a ship which reads how much water passes below the ship. This sends a signal a computer, which records the process. It seems that there is a slight problem with this method, since water currents fluctuate often and thus the actual distance over ground is different.
I wonder how many ships became lost due to changes in ocean currents. It strikes me that there must have been some significant discrepancy at times. I imagine this is why so many ships became lost in the Bermuda Triangle; perhaps because the currents underwater change so often that a ship cannot get proper bearings and gets lost. I kind of hope that this is still a problem in the Bermuda Triangle, since large ships becoming inexplicably lost is part of what gives the ocean its sense of mystery, wouldn't you agree?