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Re: Silicon Sea: Leg 77
From: Michael Wescott
Date: 2001 Jul 25, 8:29 PM

```> Promptly at Sunrise on 24/06/2001 we raise anchor at Isl Flamenco
> (08d 55.2'N  79d 31.6'W) and head for our departure point at Isla
> San Jose Light(08d 10,5'N  79d 31.6'W) motoring.

Is Isla San Jose Light truly due south of our anchorage?

> Speed = SQRT LWL x 1.34

> 1)  What is the Zone Time (ZT) of our Estimated Time of Arrival(ETA)
>     at the Isla San Jose Light?

>     What is the UT/GMT ETA?
> --  ----------------------------------------------------------------
Sunrise at Isl Flamenco should be:
0541 (Almanac entry for 10d N)
+  2 (Interpolation for Latitude)
+ 18 (4d 31.6'west of center of zone)
====
0601

Speed is 1.34 sqrt(39) = 8.4 kn

Dist = 44.7 mi (by inspection)

Time en route = 44.7/8.4 = 5.32 hr (5h 19m)

ETA = 1120 ZT (GMT-5)
= 1620 UTC

> On our ETA at Isla San Jose we take a departure FIX off of the light that is
> (08d 55.2'N  079d 29.4'W). We set our course for the Mid-Ocean Point(MOP) at
> (03d 00.0'N  110d 00.0'W).

Been motoring in circles, have we? We're only a couple of miles from
our anchorage.

> Variation 2.0dW, Dev 0.5dE. Drift 0.6 Kts Set 285.0d. Speed 10.1 Kts.

> 2)  What is the TC and Distance from Isla San Jose Light to the MOP?
> --  ----------------------------------------------------------------

dLat = 355.2'
dLo = 1830.6'
dep = dLo * cos 6 = 1820.6
arctan(355.2/1820.6) = 11d
sqrt(355.2^2 + 1820.6^2) = 1854.9

C=259T, D=1854.9

> We plot our track on INT Chart 811 and see that we can not head direct for
> the MOP(03d 00.0'N  110d 00.0'W) without crossing land above Punta Mala in
> Panama. So we alter course to MOP2 at (05d 00.0'N  80d 00.0'W).

> Variation 2.0dW, Dev 0.5dE. Drift 0.6 Kts Set 285.0d. Speed 10.1 Kts.

> 3)  What is the True Course and distance to MOP2?
>     What is the Compass Course(CC)/Course-to-Steer?
> --  -----------------------------------------------

Assuming the course changed at 08d 55.2'N  079d 29.4'W, i.e. immediately.

dLat = 235.2
dLo = 30.6
dep = 30.6 * cos 7 = 30.4
arctan (235.2/30.4) = 82.6
sqrt (30.4^2 + 235.2^2) = 237.2

D = 237.2
C = 187.4T = 189.4M = 188.9C

Correcting for current (plotting sheet)

C = 184T = 186M = 185.5C

> At 14:45:30UT the next morning we take a SUN LL sight. Other Data as above.

>     Hs 47d 54.6''

> 4)  What is the DR position?
> --  ------------------------
dTime = 2400 + 1445 - 1620 = 2225 = 22.4 hr
D = 10.1 * 22.4 = 226.24

dLat = cos 187.4 * 226.24 = 224.4'S
dep = sin 187.4 * 226.24 = 29.1 mi W
dLo = 29.1/cos 7 = 29.3'W
DR = 5d 10.8'N  79d 58.7'W

> At 22:45:23UT we take another sight of the SUN LL

>     Hs 15d 34.3'

> 5)  What is the DR position?
> --  ------------------------
dTime = 2245 - 1445 = 8hrs
D = 10.1 * 8 = 80.8 mi
dLat =  cos 187.4 * 80.8 = 80.1'S
dep = sin 187.4 * 80.8 = 10.4 mi W
dLo = 10.4/cos 4.5 = 10.4'W

DR = 3d 50.7'N    80d 09.6'W

> 6)  What is the Running FIX(RFIX) position at the 22:35:23UT sight?
> --  ---------------------------------------------------------------

Which is wrong, this time or the  22:45:23 above?

At 22:35:23, I get a Ho = 12d 31.7' at the DR.
At 22:45:23, I get a Ho = 10d 14.0' at the DR.

Something is way off. Was the time actually 22:25:23?

> Checking our Running FIX against the position of MOP2(05d 00.0'N  080d
> 00.0'W) it seems we have passed MOP2. So we alter course to our original Mid-
> Ocean Point which we re-name MOP1(03d 00.0'N  110d 00.0'W).

> Speed 10.5 Kts. Current Set 285, Drift 0.6 Kts. Var 1dW Dev 2dE.

> 7)  What is the TC and Dist to the MOP1(03d 00.0'N  110d 00.0'W)?
>     What is the Compass Course(CC)/Course-to-Steer?
> --  -------------------------------------------------------------

Form DR 3d 50.7'N    80d 09.6'W to MOP1:

dLat = 50.7'
dLo = 29d 50.4' = 1790.4
dep = 1790.4 * cos 3.5 = 1787.1
arctan(50.7/1787.1) = 1.6

C = 268.4T = 269.4M = 267.4C
D = sqrt(1787.1^2 + 50.7^2) = 1787.8

Correcting for current (plotting sheet):

C = 267T = 268M = 266C
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