NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Wind & Current Navigation
From: Herbert Prinz
Date: 2003 Apr 17, 18:20 +0000
From: Herbert Prinz
Date: 2003 Apr 17, 18:20 +0000
Trevor, You are right on target with your analysis. I was just about to say the very same thing, except that I would give a little more attention to these first critical seconds right after releasing the dock lines. Dan's problem is trivial in so far as the current comes from dead astern. But in the general case an athward current will introduce a rotational forces on the boat until the boat reaches the speed of the water. Other than walking out the boat with lines, installing a bow thruster, or using as much throttle as possible and pray, I would be interested to know what can be done about it. As I have emphasized in my previous message, and George and you have pointed out again, the biggest problem is that the current that prevails one boat length away from the slip is likely to be very different from what it was in the slip, again, causing the boat to spin. I also think that it is unnecessary to analyse the problem in terms of forces. Course and speed vector diagrams are sufficient because the forces cancel out: If the winddrag force increases with the square of the wind speed, so does the drag force through the water with boat speed. I looked at a diagram in Kotsch and Henderson, "Heavy Weather Guide", 1984, p.282, showing leeway of a liferaft versus wind speed. The dependence is almost perfectly linear. Herbert Prinz "Trevor J. Kenchington" wrote: > Dan, > > It may sound silly but think you are asking the wrong questions. [...]