… is the evidence it provides about boats and inland waterways.
Here is an unreliable link to a painting called Grand Canal Harbour [click on the image to enlarge it] by Flora Mitchell. If the link doesn’t work, use this, which seems to be less flaky, and enter the two words canal and mitchell in the Quick Search box; you should get two thumbnails of canal paintings by Flora Mitchell.
[updated 20140922]
Irish waterways history 
That link is not working Brian.
Thanks. I may have fixed it, but it seems a bit unreliable. If it doesn’t work, go here and put the two words
canal
mitchell
in the search box. You’ll get two images, one of which shows the harbour. bjg