Don't know a whole lot about how they were used. Nets were reeled out the stern and left overnight. Then reeled back in with a lot of fish in them. Gilnets perhaps? Small engines, they just chug along at hull speed. The really old ones were built of wood.
Civil War boats. Remember the Monitor and the Merrimac?
These are net boats. They pull in the nets from the side, obviously, with the doors open.
These boats are still seen in use today in the Great Lakes. They sure protect the fishermen from the nasty weather.
I think if you were to drive the Agnes H into New London harbor nowadays, you might find yourself receiving a not so warm welcome by the authorities. Interesting stuff. I have never seen this type of vessel before. Thanks for posting it.