Yes I read that post and I like the idea that you get a high...

Yes I read that post and I like the idea that you get a high exposure population. But I can also see it may not be practical. E.g Day 1- find out about ship. Day 2-3 produce trial plan. Day 4-11 - get some kind of approval from Tga to proceed with trial. Also come up with a safety plan of how you going to get personnel on the ship to conduct pre- trial screening and take mid-trial blood work etc. Day off the12 start conducting pretrial screening and accepting participants. Now anyone who contracts covid in the next 14 days has potentially already been exposed prior to the start of the trial. You are already a month in to this and you might find that a large % tests positive prior to the test really starting. Then what if you find that during the trial one location of the ship gets more heavily infected. E.g. everyone on deck3. Has that skewed the rest results? Even if we don't think so, tga might.
A trial that gives inconclusive or questionable results might damage the brand and future trials. You can't choose to ignore the test results if it turns into a mess.
I like the out of the box thinking, but I can also see potential issues.
My opinion only. DYOR I am certainly not an expert.