Hi HarleyJohn,
I think it's great what you are doing. I'm on the west coast and have worked a number of years (18 to be exact) as an architectural draftsman. Building codes may not match the east coast but I assume it will be similar considering both are interpretations of the ADA handbook. Here are a few things to consider:

---RAMPS
-Make ramps a 1:12 slope. Ie, for every inch rise, 12 inches vertical. So, ramps from dock to boat should be 1:12.
-Ramps, passageways, aisles should be 36" wide.
-Landing should have 5' turn radius. Basically a 5'x5' square at the bottom and top of a ramp for them to turn around.
-Ramps should have some form of non-slick surface.

---Handrails
-Handrails should be 36" high.
-Handrails should have a minimum of 300 lbs of deflection. Ie, able to handle 300lbs without twisting.
-Both sides of Ramps should have a handrail but one side should extend at least 12" beyond ramp.

There are too many restrictions on bathrooms. So, I won't put it here. Also, I don't think you'll want a bathroom? But, you might think of putting some kind of way to secure wheelchairs as they usually use seatbelts for both securing the people and their chairs.