wrote:
What frequencies would have been used for communications? HF? VHF?

http://www.boatnerd.com/

http://cimss.ssec.wisc.edu/wxwise/fitz.html

"At 7 p.m. the Anderson made radio contact with the Fitzgerald and had
her on their radar. When asked how the Fitzgerald was making out they
replied "We are holding our own". This was around 7:10 p.m.. Shortly
afterwards the Fitzgerald disappeared from the Anderson's radar
screen."

Thanks to a link at Trainorders.com for the tip.

The ships also had radar, although at some point both radar units on
the Fitzgerald were knocked out. The Anderson was in more or less
constant contact by radio.

Discovery Channel ran their well done program on the sinking of the
Edmund Fitzgerald not too long ago. As I remember it a shift in wind
direction meant the ships were no longer protected by the coastline
they were hugging for protection. The huge waves gradually flooded the
heavily loaded ore ship, making it sit even lower in the water. A big
wave probably did the ship in.