This would be appropriate for river boats or floating restaurant/casinos etc that only went up and down river a mile or so.

It would float with the river going downstream, but to go upstream, it would deploy a metal underwater "sail" that would be attached to a cable looped around a pulley, the other end of the cable being attached to the boat. The water sail would have a larger surface area than the boat resulting in it being pulled downstream while the boat went upstream.

When the boat was upstream and ready to come back, the sail would be flipped parallel to the water so the boat would now have the greater resistance of the two objects and the boat would come back to it's starting position.

My first idea was to have a zig/zag track along the river bed that the boat would "tack" along to go upstream, then when upstream the boat would just turn directly into the stream and zig zag back but I think the cable/sail would be a lot easier and cheaper.

You could also make this a straight funicular arrangement with two boats cabled together around the pulley and just open flaps on the downstream moving boat or turn it perpendicular to the water's flow while the upstream boat was parallel.

Be a nice way to go up and down a river with no noise, pollution or fuel costs.
-- doctorremulac3, Aug 09 2012

From 1840 to 1877, a chain-operated tug operated on the Thames between Tower Bridge and Blackfriars, with the winch (first horse-powered, but later driven by a waterwheel in the Thames itself) at the Blackfriars end. The chain was made of wrought iron links, each about a yard long. A barge was permanently attached to the chain, and other boats could tie themselves to the barge to be towed up-river, for a fee. It was operated and controlled, for reasons that are arcane and obscure, by the Guild of Lorimers.

After it fell into disuse, the chain itself was left on the bed of the Thames. It's still there, and is occasionally snagged by dredgers or by dragging anchors. A section of it was hauled up in 1973, and was found to be in virtually pristine condition.
-- MaxwellBuchanan, Aug 09 2012


Or you could just do it Bangkok style-ee where express boats zoom along the river in a zig-zag fashion, to each stopping point, hopefully avoiding each other, the bulk carriers and the really little ferry boats. The little boats have a totally inadequate number of lifebelts, each held into the overhead racks by twisted wire no one could possibly undo in an emergency.

Each stop must be made at a fixed jetty, or a swinging one which never, ever quite matches the up and down movements of the boats, as the boats themselves shift laterally in a manner to give an instant diet to anyone who falls between the boat and jetty.
-- not_morrison_rm, Aug 10 2012



random, halfbakery