Running charters for 20+ years I was in potential collision situations more than I care to admit. Fortunately only once would have been my fault, but very scary, a dive boat in open water 10 miles offshore anchored in my blind spot where I would never have guessed a boat to be. I would always tell the guests during my briefing, even though I am the Capt I am not infallible and if you see something like another boat approaching too close, I have no issues with you mentioning it and I would prefer you would. I would say of my near collisions, about 40% were a result of no one at the helm (not just bareboat, but professional crewed boats), I would make sure I scared the crap out them them by passing close astern and doubted they made that mistake again.