a make shift launching ramp, as you stated.
Ric, they wrote the caption, not me. But I agree with your observations. It does look as if the boat is tied to a cradle typical of a marine railway (just like an ordinary railway, except broad gauge and it runs into the water. I have pics of the extensive marine railway in Rock Hall, if anyone is interested.) The rear flatcar looks to be the interface between the wide gauge ‘railway’ on the middle flatcar carrying the boat, and the actual rail tracks that lead in to the water.
From the fact that the loco is on track that looks fairly permanent, this may have been a trans-shipment point for boats being hauled between the lakes and other places. Just as we now use flatbed trailers.
So I googled “delaware and hudson boat launch in baldwin, NY” (the loco has D & …) and found that not only was there a boat yard in Baldwin, but the big lake steamboats were built there. The same photo is on the page (see link below) and has a more descriptive label:
The Delaware and Hudson Railroad assigns a Dickson-built Mogul No. 313 to deliver the steam yacht “Ellide” to Baldwin Dock in the 1890s. The boat rides on a flatcar along a makeshift launching track near the steamboat dock. A winch on the flat car allows the boat to roll gently down the ramp into the water. The D&H maintained a similar permanent “marine track” in the village of Lake George (Caldwell). (Fred Thatcher photo, Delaware & Hudson by Jim Shaughnessy, M. Wright collection)
http://www.tibranch.com/tibranchmain.html