If you have been on the Aire and Calder when barges are coming - and they can come very fast, well above the limit - you know they are coming from the wave that often arrives well before the boat does.
--- On Fri, 7/18/08, Mack, David <[EMAIL PROTECTED]> wrote: From: Mack, David <[EMAIL PROTECTED]> Subject: RE: [canals-list] Re: Soliton To: [email protected] Date: Friday, July 18, 2008, 12:14 PM 2008/7/17 Brian J Goggin [EMAIL PROTECTED] ie: > >> "Having reached the highest level of the great table-land, we > >> traversed a space of fifteen miles without a lock; and > here a curious > >> phenomenon, illustrating the incompressibility of water, > arrested our > >> attention. About every twenty or thirty minutes, the horses are > >> obliged to stop for five or six minutes, to take breath, > the cause of > >> which was this: --- The velocity of the boat impelled the > water with > >> such force that it gradually rose so as to approach the summits of > >> the banks, when it began to recoil, so as actually to form a > >> back-water or stream, when the horses were unable to make > head, and > >> therefore stopped until the equilibrium of the canal was restored." > >> > >> I have not heard of that phenomenon before. Has anyone else come > >> across it? > > > >I think everybody who has tried to go too fast along a narrow and > >shallow canal has suffered from this effect. Adrian added > A soliton is a single wave. Once created (and moving) it > keeps moving along the channel at a surprisingly high speed > and for a surprisingly > long time. It is a short (measured along the direction in which it > is travelling) hump in the surface -- i.e. the water level > rises briefly as it passes, and immediately returns to its > previous level once it has passed. > > The "tide" effect is quite different. It is a long-lasting (and > increasing) rise in the water level of a long length of > waterway ahead of oncoming traffic, which can occur in > unusual circumstances as described in the quote above. It is > not a wave at all. A thought occurs to me: If a boat which occupies a large proportion of the channel cross section is hauled from the bank, there will be a tendency to push the water ahead. So if the length of the pound is limited the water will build up, possibly to the point where you really are trying to pull the boat uphill. This would seem to be what is described above. However, if the boat is motor driven, the propeller takes water from in front of the boat and pushes it out behind, so the build-up of water occurs behind the boat, and you are in a sense travelling downhill. Which is why those of us in powered craft never experience the effect. David Mack [Non-text portions of this message have been removed]
