That's quite a load, particularly if you're not regularly practicing humping that kind of weight for any length of time. Well, I'm not sure how far you're planning on needing to walk with your BOB.

Just a thought--I know space is at a premium on a boat, but perhaps you could consider some sort of cart? As far as something folding goes, something like those tall folding laundry/grocery carts, like this , could take the weight off you. Keep the most essential stuff on your person in case you needed to drop everything and sprint away, but you should be able to last a lot longer without having to actually carry all of that weight the whole time.

When I lived in NYC, it's typical for people to have to haul their laundry up and down many flights of stairs (I lived in a 5th floor "walk-up" apartment) and a few blocks away to the nearest coin laundry. Many carts are small and cheaply made, but I had a large, really sturdy folding cart that seemed like it should hold 50 pounds securely. If the handles are tall enough, you should be able to push the cart in front of you comfortably, almost like a supermarket shopping cart, otherwise you'd have to hunch over some or else improvise some higher handles. You could pull it behind you one-handed, but that's awkward over long distances. You could set up some straps to pull it behind you, but the balance of the cart would be tricky.

And this is not to say that you couldn't have a cart and an ALICE pack, too. Anyway, just an idea.