I am only thinking out loud. A wider angle lens would let you set up closer to the boat and still get it in the frame, and at the same time require you to focus closer.
While every camera is obedient to the same laws of DoF, not everything is possible with a given camera or maybe even any camera. If I need an f/0.3 lens to get the DoF I want, I had better make other plans. If I need a 20mm lens for my 4x5, probably not going to happen. And so forth.
I decide the shot I want, and do some math. If what I need isn't available to me, I move on.
My wife wanted to take a photo of a woman who repairs musical instruments. The woman worked in a room about the size of a small closet. How do you get a camera on a tripod inside a "shoe box" with a woman working on a cello? And use a couple of strobes with soft boxes? And get everything in focus? And use the Hasselblad she owns with one of the three lenses she owns? Think, plan, and sacrifice some of the things you "need."
"In any event, I'm still waiting on you professionals to get a picture given my parameters above to see how high dollalar [sic] cameras stack up given a large subject, very limited space to 'move away' from the subject, and shallow DOF." What is your budget for this assignment, and how much do I get?
Seriously, move some boats. Get (buy, borrow, rent) a different, more flexible or suitable camera. Get in a boat to get where you need to be. Shoot on a foggy day when the backgound will be fuzzier.