So, there are around 60000 merchant vessels, and 4 million fishing vessels. If we line them up aft to prow and make the height differences work somehow, assuming an average of 100 meters for the merchant vessels and 25m for the fishing vessels this would allow us to cover around 16000km of the equator, which would leave 12000km of open water. So, if my sources are not too wrong, and if I didn't fuck up the calculations, around 7.5 million people would die. Less if you sent the people with the biggest arm span to the open water. I say it would be worth it. this would allow us to make floating bridges over the ocean for every one.
I think you've tripped up with your numbers somewhere. Four million fishing vessels averaging 25m each gives you 100,000km, enough to circle the entire Earth twice over with plenty to spare