In "Stolen Ingots" in Dr. Thorndyke's Case-Book by R. Austin Freeman, there was a boat that chases a barge in a tidal river and amongst muddy banks:
Meanwhile the fugitive barge, having got some two miles start, seemed to be drawing ahead. But it was only at intervals that we could see her, for the tide was falling fast and we were mostly hemmed in by the high, muddy banks. Only when we entered a straight reach of the river could we see her sails over the land; and every time that she came into view, she appeared perceptibly smaller.
"Still gaining?" asked Badger.
"Aye. She's a-going to slip across the tail of Foulness Sand into the deep channel. And that's the last we shall see of her."
"But can't we get into the channel the same way?" demanded Badger.
"Well, d'ye see," replied the fisherman, "'tis like this. Tide's a-running out, but there'll be enough for her. It'll just carry her out through the Whitaker Channel and across the spit. Then it'll turn, and up she'll go, London way, on the flood. But we shall catch the flood-tide in the Whitaker Channel, and a rare old job we'll have to get out; and when we do get out, that barge'll be miles away."
How could its sails be over the land?!
And as for the second bolded sentence "Then it'll turn, and up she'll go, London way, on the flood."
It's a bit obscure for me because of these too much commas! Does it mean "the tide will turn london way, and she will go on the flood"? or "she herself will go london way?!
And for the last bolded thing, what's meant by "rare old job"?