Mack, David wrote: > 2008/7/17 Brian J Goggin [EMAIL PROTECTED]: > > 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.
More likely that most boats are relativity shallow these days, leaving enough room underneath for the water to flow back. You are not going to move 30 tons of water with a propeller in 70ft... The amount the prop moves is negligible to the amount of water that is needed to be moved. Ron Jones Process Safety & Development Specialist Don't repeat history, unreported chemical lab/plant near misses at http://www.crhf.org.uk Only two things are certain: The universe and human stupidity; and I'm not certain about the universe. ~ Albert Einstein
