# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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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. [...]

```
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