Upvote:3
There is a bigger version of this map here: http://www.bl.uk/onlinegallery/onlineex/unvbrit/g/zoomify82848.html
No.1 is a wheel with a crank on it and the two men appear to be holding a cable so perhaps it's used to pull boats down that canal.
No.2 is almost certainly some kind of sea defence. It doesn't have guns on it so could be like a sea wall, designed to protect the entrance of the estuary from erosion. The stand alone one on the river is possibly a wall to protect ships at anchor near Little Yarmouth. The black could indicate infill of rocks or dirt.
What's also interesting is the crane near the bridge. I guess this has a practical purpose but it appears that it's being used here to entertain people with a person being hoisted into the air while others run around the base.