NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Speed and waterline length. was: Revisiting hull pressure wave
From: George Huxtable
Date: 2005 Jan 27, 20:17 +0000
From: George Huxtable
Date: 2005 Jan 27, 20:17 +0000
Jared wrote- >Bill, I would expect your "downward pressure wave" is the same as the >"ground effect" which gives aircraft extra apparent lift when they are about >to land. And for that matter, when two boats under way come alongside, >there's a point where the water between them also seems to help buffer them >apart. > >In every instance you're seeing a point where the fluid (water or air) >simply isn't being displaced but is being forced back by another object (the >runway, the bottom, the other craft) and the flow is changing. Comment from George- Well, the problem about that is that when two vessels travelling together in parallel get too close, they tend to see an ATTRACTION that draws them closer; a dangerous state of affairs, that has in the past given rise to collisions, and about which our Maritime Safety Authority has issued a warning. It makes naval refuelling-under-way from ship to ship particularly tricky. Anyone in a small craft who has been overtaken by a large vessel in a narrow waterway will know what I mean. It takes some hard helming to keep away. So that's a force acting in the opposite sense to the apparent extra lift that Jared describes for an aircraft on landing. I wouldn't argue that these effects are unconnected: there may indeed be a common mechanism behind them both. But it can't be quite as simple as Jared makes out. George. ================================================================ contact George Huxtable by email at george@huxtable.u-net.com, by phone at 01865 820222 (from outside UK, +44 1865 820222), or by mail at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK. ================================================================