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

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Re: Silicon Sea: Leg 79
From: Michael Wescott
Date: 2001 Sep 28, 12:16 PM

```> > TC 270.0d, Speed 10.0 Kts, Current Drift 1.0 Kts, Set 280.0d. Var
> 2.0dE,
> > Dev 1.5dE.
> >
> > 4)  What is the Compass Course(CC)/Course-to-Steer to MOP1(03d 00.0'N
> >     110d 00.0'W) from the FIX position?
> > --  -----------------------------------------------------------------
>
> From-   3d 28' N         97d 18' W
> To:     3d  0' N        110d 00' W
>        ----------------------------
>     dLat = 28' S  dLon = 12d 42' W = 762' W
>
> Taking departure = dLon, and using a rule of thumb that
> sin(x degrees) = tan(x degrees) = x/60 for small angles,
> our true course is 60*28/762 = 2.2 degrees south of due west.
> The current sets us 1.0*sin(7.8d)=.13nm to the left each hour,

Nope, currents sets us 1.0*sin(12.2)=.21 nm to the *right*.

> during which we travel 11 miles, so we need to adjust course
> to the right 60*.13/11 = 0.7 degrees.  Adding it all up,

To the *left* 60*.21/11 = 1.1 degrees.

> CCTS = TC + current + var + dev
> CCTS = 270 - 2.2 + 0.7 - 2.0 - 1.5 = 265d

CCTS = 270 - 2.2 - 1.1 - 2.0 - 1.5 = 263.2 (very close for all the
approximations).

--
Mike Wescott
Wescott_Mike@EMC.COM
```
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