There are two ways that come to mind. As I noted before, the best way would be to use the programming software and proper cable to read the radio programming. As long as there was no read password, you could get all of the information that you need.
The second option would be to use a scanner with a "close call" feature (ability to scan through a defined range of frequencies at a very high rate) while you are transmitting with the radio. this would need to be done on each channel. Unfortunately, this won't help you in determining what frequencies the radio is receive on each channel. The scanner would also need to be able to determine squelch codes if those are programmed into the radio as well.
You'd need to proceed with caution using the second method: You mentioned that this radio is used on a boat if I recall. If the radio is programmed with marine frequencies, you could potentially be transmitting on emergency or Coast Guard channels. If so, you might find yourself the recipient of unwanted attention.
I'd suggest the former option. If there is a two way radio company in your area, they might be able to help you with reading the radio.