If he had a spotter with a pair of binoculars then he would have been in line of sight but I don't really think that authorities would object to a flight over water, but he had flown directly over the vessel but not within 50 metres and that is not a violation of current rulings CAA rulings which state :- Never fly closer than 50m to buildings, cars, trains or boats.
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However, on his return prior to landing it could be argued that he possibly overflew structures and people but the 50 metre rule still applies.
I wonder if he has any insurance. Not a bad thing to have 'just in case' but if he broke the drone code rules the insurance might be null and void. That's when you HAVE to read the small print to find out.
Suppose a
Mavic 2 Pro failed in mid air and hit a person and caused damage. That person would have to sue the pilot and I have heard of a case where the pilot had to sell his home and business to pay for the medical bill and more, so its best to be safe than sorry.
That's my understanding of the rules and regs in the UK. Maybe I am wrong but all the above is a moot point really since the rules and regs are being 'modified' later on in the year.
Who is right and who is wrong in ANY case would be up to the legal lads to decide at the end of the day but
wise pilots don't temp fate and use common sense to avoid any possible confrontation with anyone.