One rental agency in my area has built a dock extension that is sunken in the middle to below water level by about 8 in. You simple carry your boat down the dock, walk down the stairs onto the sunken platform and get in your boat. The extension is wide enough for two boats to be side by side with the regular height dock on either side. Only drawback is that quite often, they have to clean the submerged platform of the algea and seaweed as it gets quite slippery. I think had they made the sunken platform out of something like aluminum non-slip open grating, it might be easier to maintain and single lips would have been better so the person entering could stablize themselves by holding onto the dock sides. This of course is in an area in which there is no or very little beach access so it works.