We were thinking of this last year but never completed the research. Thinking ahead for the future and many years at the lake, someday those stairs will be too much.
Here are some of the sites we were using for ideas.
http://marineinnovations.reachlocal...._campaign=tram
http://www.wannaliftsystems.com/tramsystems.html
This one has a few collected in one place:
http://www.top20sites.com/Top-Hillside-Lifts-Sites