Now, for why someone would need/make something like this, I have one word:
A smaller version of this device would be a godsend, as the best chainmail armor had riveted links. I've make chainmail the lazy way, by squishing links together with pliers, and that was tedious enough. I can't imagine the amount of work required to make a riveted suit with medieval technology... Go to Comment
Interesting, though I am reminded of the sharks in Finding Nemo.... Personally I think vampires should not be sugar-coated. They are anti-life and evil. But that's my opinion.
There are blatant spelling errors that should be addressed and some of the sentence structures need rewor - like
"In a world where rival vampires would like to get you out of the way to be on the safe side and where the inquisition hunts anything not 'natural' not to mention fledgling vampire slayers trying to start on less vicious vamps first they find there is safety in numbers. "
This should be three sentences - too much is being conveyed in one.
My advice - Take Moonhunter's Advice wholeheartedly. Go to Comment
Another quality item here - and the 'attraction' to storms could be very subtle. It would be those captains who are a little more tolerant of bad weather that would be in greater danger, for - magic or no - a storm takes time to come close.
It may be subtle enough that the locals who use these sails simply build sturdier ships over time - shipwrights who built too frail ships would be eventually driven out.