Gosh I don't know about a boat, it's a whole cruise ship that's needed. So many unhappy posters. So many shocking stories. 
I jumped off the diving board 5 years ago, after at least 4 years of knowing it was over. All the pleasure in life had drained away so that when I qualified (after studying for 13 years) I couldn't feel the joy I'd always thought I'd feel and had looked forward to in all those years of training. I felt I'd betrayed myself by staying with such a nasty, sulky, moody, belittling, deceitful, selfish shit. That's when I made up my mind.
I was terrified of going, I wasn't sure I could cope on my own, which was ridiculous because I had always been independent and capable before I married. I was worried about money, dc, work, failing. But it really wasn't that hard once I went and the peace of mind and freedom were and still are wonderful.
My only regret now? That I didn't leave sooner.
You CAN leave. Take it one step at a time. And soon you will realise that you have a plan. You don't need to have a conversation necessarily (and i bet you know what they'll say anyway). Just make your plan, one step at a time.