Upper and/or Lower SSB Quest. ? And 2182 Quest. ?
 

All MHF and HF maritime SSB comm is USB. LSB has also been used for a certain
other type of service other than voice. It's been so long since I worked with
maritime stuff I don't recall what the other use is.

The most common MHF working frequency, after calling on 2182, is 2638.

Bill, K5BY