The answer to your questions are:
Yes, they're
supposed to be on and monitored.
That may not be what we do all the time; but, the question of
"should" is not in doubt. If something bad happens, and you didn't have the VHF, Radar, AIS, a watch posted and watching, etc., then you didn't do everything possible. Because something bad happened, you can argue that it wasn't possible for "bad to happen"...
There is a legal doctrine:
res ipsa loquitur
(rayz ip-sah loh-quit-her) n. Latin for "the thing speaks for itself," a doctrine of law that one is presumed to be negligent if he/she/it had exclusive control of whatever caused the injury even though there is no specific evidence of an act of negligence, and without negligence the accident would not have happened. Examples: a) a load of bricks on the roof of a building being constructed by Highrise Construction Co. falls and injures Paul Pedestrian below, and Highrise is liable for Pedestrian's injury even though no one saw the load fall. b) While under anesthetic, Isabel Patient's nerve in her arm is damaged although it was not part of the surgical procedure, and she is unaware of which of a dozen medical people in the room caused the damage. Under res ipsa loquitur all those connected with the operation are liable for negligence. Lawyers often shorten the doctrine to "res ips," and find it a handy shorthand for a complex doctrine.
The USCG guidance on the matter is pretty clear. ;^))) For ease of discussions: Here are USCG guidance on the subject:
The USCG "answers to frequently asked questions states:
"
11. 33 CFR 164.35), however, Rule 7 states that proper use shall be made of radar equipment if fitted and operational. In other words, whoever has one must use it. The Navigation Rules are not meant to discourage the use of any device, rather they expect prudent mariners to avail themselves of all available means appropriate...as to make full appraisal of the situation (Rule 5), e.g. the use of radar. At issue is whether the use of radar is appropriate in the prevailing circumstances and that is a determination made by the Master; and, ultimately decided by a trier of fact."
"Should you be in a collision how would a judge/jury rule on your contention that the use of radar was impracticable (due to electrical drain, crew shortages, etc.)? Also, if a collision does occur, then there was obviously a risk of collision beforehand. Could the determination of that risk have been made sooner with the use of radar? It is difficult to answer such questions because the circumstances of each case are different."
"More importantly, remember that Rule 7 specifies that assumptions shall not be made on the basis of scanty information, especially scanty radar information."
"Should you be in a collision how would a judge/jury rule on your contention that the use of radar was impracticable (due to electrical drain, crew shortages, etc.)? Also, if a collision does occur, then there was obviously a risk of collision beforehand. Could the determination of that risk have been made sooner with the use of radar? It is difficult to answer such questions because the circumstances of each case are different." [res ips?]
"More importantly, remember that Rule 7 specifies that assumptions shall not be made on the basis of scanty information, especially scanty radar information."
Radio Watchkeeping Regulations
In general, any vessel equipped with a VHF marine radiotelephone (whether voluntarily or required to) must maintain a watch on channel 16 (156.800 MHz) whenever the radiotelephone is not being used to communicate.
Source: FCC 47 CFR §§ 80.148, 80.310, NTIA Manual 8.2.29.6.c(2)(e), ITU RR 31.18, 52.244
In addition, every power-driven vessel of 20 meters or over in length or of 100 tons and upwards carrying one or more passengers for hire, or a towing vessel of 26 feet or over in length, as well, as every dredge and floating plant operating near a channel or fairway, must also maintain a watch on channel 13 (156.650 MHz) --channel 67 (156.375 MHz) if operating on the lower Mississippi River-- ; while navigating on U.S. waters (which include the territorial sea, internal waters that are subject to tidal influence, and, those not subject to tidal influence but that are used or are determined to be capable of being used for substantial interstate or foreign commerce). Sequential monitoring techniques (scanners) alone cannot be used to meet this requirement; two radios (including portable radios, i.e. handhelds) or one radio with two receivers, are required. These vessels must also maintain a watch on the designated Vessel Traffic Service (VTS) frequency, in lieu of maintaining watch on channel 16, while transiting within a VTS area. See 33 CFR §§ 2.36, 26, and 161; 47 CFR §§ 80.148, 80.308-309; NTIA: NTIA Manual Chapter 8.2.29.7.
Digital Selective Calling
Ships, where so equipped, shall, while at sea, maintain an automatic digital selective calling watch on the appropriate distress & safety calling frequencies [e.g. channel 70] in the frequency bands in which they are operating. If operating in a GMDSS Sea Area A1 may discontinue their watch on channel 16. However, ships, where so equipped, shall also maintain watch on the appropriate frequencies for the automatic reception of transmissions of meteorological and navigational warnings and other urgent information for ships.
Ship stations complying with these provisions should, where practicable, maintain a watch on the frequency 156.650 MHz for communications related to the safety of navigation.
ITU RR 31.18, 25.244
P.S. - The UCCG used the 'e.g.' above. That wasn't 'i.e.'
If you were driving a car in the fog, and you felt you had the right to go the "speed limit" and you hit something -- do you think that you could argue that you were not going to fast? You might have some excuses, but not good reasons. Rez ipsa locitur.