Flat Earth Spokesmen are already avoiding answering that question with sound science and common sense on a different thread here:
http://theflatearthsociety.org/forum/index.php?topic=27988.0Good luck. As I write this sentence, all you'll hear/see is unsound, scientifically unprovable tales about how light bends upward but only bends upward for some objects (boats) but not for mountains.
I gave this site a chance. I gave this theory a true hearing. So far, it's a bunch of time-wasting people whose circular "logic" contradicts itself and for which science is wholly lacking. I am still listening, waiting to see if any of the Flat Earth people actually have a leg to stand on. But it's appearing like the lot of them are basing their arguments on ideas that defy the laws of nature, the laws of physics, the laws of physical science and the credo of common sense. Perhaps someone new will show up to elucidate the (so far) well-evaded attempts to get to the bottom of this. But so far it's looking like this site is a collosal attempt on the part of bored people to waste their own lives and the lives of others for no other reason than self-amusement and/or self-aggrandizement.
Anyway, feel free to review that thread I linked above to see unsound non-answers to this question of ships at sea. If nothing else, you'll likely conclude as I have that these folks are very insincere in their alleged beliefs and are simply playing a game to see how many suckers' time they can squander.