This sounds like it was built by an old sailboater. I don't see a see of use for a seacock on an above water discharge through hull on a trawler. Unlike a sailboat, you're not going to be healed way over on one side for hours at a time.
There also sounds like some redundancy. 3 for the generator? There is an intake and a discharge. What would the 3rd by for?
ABYC requires seacocks on throughulls on power boats that will be under water at 7 degrees of heel, which is quite common when heeling in beam seas. Many throughulls which are several inches above the waterline disappear under the wake while moving. Transport Canad requires a "reliable means of closure on all hull penetrations".