The 'as well as by all available means' is part a list of three ...
Maintain a proper lookout by:
1. sight, and
2. hearing, as well as
3. by all available means appropriate in the prevailing circumstances and conditions'
So, I agree that the 'by all available means appropriate in the prevailing circumstances and conditions' is its own item.
But 'so as to make a full appraisal of the situation and of the risk of collision' does not apply to each of the three individually. In other words, we aren't required three-fold redundancy where either of the methods alone will 'make a full appraisal...' and we just so happen to be executing all three. What is required is that the net effect of all three will 'make a full appraisal...' and not necessarily anymore.
For the purpose of preventing collision with a large, slow moving freighter or a 36 foot sailboat ... as were the examples given ... it is sufficient to prevent collision with those vessels given that the assumptions made are accurate. Visibility to the horizon and zero sea state in the middle of the open ocean where expected traffic is somewhat predictable is certainly not reasonable assumption in most cases.
I would be more than comfortable with a 20 minute look interval as mentioned above is most conditions. I agree that 45 minutes might seem a little long but my point was pointing out a method to evaluate what a 'proper lookout' is. Maintaining constant visual scanning is not necessary to maintain a proper visual lookout. Further, if equipped with radar and AIS I don't see a major safety concern with a 45 minute look interval, while short handed. It certainly is better to have thought and reason behind it than to simply shrug and say 'I can take a 2 hour nap, it's only 2 hours'.
1981 C&C 32