Maritime search planning part 2 MILSAR 1 2005

Maritime Search Planning
Part 2


Objectives
• Maritime search planning theory and
various models (Part 1)
• Worksheet method of drift planning
including a demonstration
• Individual exercises using the worksheet
• Demonstration of Net Water Movement


Worksheet 1
Worksheet 1: Maritime Planning
INCIDENT Demonstration

Search target (description):

Liferaft – no ballast, no canopy, no drogue

LKP (lat/long):

17 00 N 110 00 E

@ Time (UTC):

041100 UTC

Hours of drift (a):

36 Hours

Search Time 052300 UTC


Worksheet 1
SEA CURRENT

Sea / tidal current/knots:

200

Sea Current vector/distance:

200

O

O

(T)

1.5

(T)

knots

1.5

x

36

(a)hrs =

knots

54

nm


Sea Current vector/distance
200

O

(T) at

1.5 knots

x

36 (a)hrs = 54 nm


Worksheet 1
SURFACE WIND and CALCULATION OF WIND CURRENT

Surface winds/knots

045 O (T)

10

knots

Reciprocal of Surface Winds/Knots (b)

225

O

10

knots

Wind current vector: (use reciprocal bearing
and divergence (Figure I-1)

36

(a) hours x 0.35

(T)

Wind Current Divergence = Reciprocal Surface Wind
+ 30o for LKP greater than 10o North Latitude

+ 30o T =

knots (Figure I-1) =

255

O

(T)

255

O

(T)

12.6

nm

10

knots


Wind Current
• The effect of sustained local winds
on the water’s surface
• Takes effect after 6 – 12 hours in a
constant direction

• Near the coast – consider omitting wind current
• Offshore – consider omitting wind current if the
area has consistent winds
• Appendix N: Figure N-1: Local Wind Current
Graph and Table

Vol 2 N-1



Wind current vector: (use reciprocal bearing
and divergence (Figure I-1)
36 (a) hours x 0.35 knots (Figure I-1) = 255 O (T) 12.6

nm


Worksheet 1
SURFACE WIND and CALCULATION OF WIND CURRENT

Surface winds/knots

045 O (T)

10

knots

Reciprocal of Surface Winds/Knots (b)

225

O

10

knots

Wind current vector: (use reciprocal bearing
and divergence (Figure I-1)

36

(a) hours x 0.35

(T)

Wind Current Divergence = Reciprocal Surface Wind
+ 30o for LKP greater than 10o North Latitude

+ 30o T =

knots (Figure I-1) =

255

255

O

(T)

12.6

O

(T)

nm

10

knots


Worksheet 1
TARGET LEEWAY

Leeway Angles (divergence)
(Table I.1 or I.2):

Reciprocal Surface Wind (b)

Leeway vector: (LW)

L W (L) - 24 =

Leeway speed: (knots) = (Multiplier x
Wind Speed) ± Modifier
(Table I.1 or I.2)

[ 0.057

Leeway distance:

(Leeway speed 0.78

201

o

Multiplier x 10

x (a)

225 o (T)

±

(T)

24

L W (R) + 24 =

Wind Speed = 0.57 ] ± 0.21

36

hrs =

28.08

nm

o

(T)

249

Modifier= 0.78

o

(T)


Leeway
The movement of an object as it is pushed through the
water by wind blowing against its exposed surfaces. The
pushing force of the wind is countered by drag on the
underwater surface.

Wind

Leeway


Calculating Leeway

Leeway speed is a percentage of wind speed based on
USCG trials on various marine targets. The formula is:
Leeway Speed (knots) = Multiplier x Wind Speed (knots) +
Modifier

Wind

Leeway


Divergence
As an object drifts its lack of symmetry will cause the
object to deflect (or diverge) to either the left or right of
the downwind direction.

r
Dive
ce
gen

Wind


Leeway – Craft Types


Leeway vector: (LW)
Leeway distance:

L W (L) - 24 =

201 o (T)

Leeway speed 0.78 x (a) 36 hrs =

28.08 nm


Leeway vector: (LW)
Leeway distance:

L W (R) + 24 =

249 o (T)

Leeway speed 0.78 x (a) 36 hrs =

28.08 nm


Worksheet 1
DRIFT ERROR

Distance (L)

90

de (L):(12.5 to 33% of Distance L)

Distance Left/Right =

22.8

nm

11.25

nm

Distance (R)

nm

De = [de (L) + de (R) + Distance L/R] / 2

85.5

de (R):(12.5 to 33% of Distance R)

De =

22.36

10.68

nm

nm

Calculation of Drift Error
• Distance (L) and Distance (R) from LKP on
chart
• de (L) and de (R) is usually 12.5% of the
distance (L) and distance (R) from LKP.
SMC may use up to 33%
• Distance Left/Right is obtained from chart


Calculation of Drift Error (De)
• De = [de (L) + de (R) + Distance L/R] ÷ 2
• De = [11.25 + 10.68 + 22.8] ÷ 2
• De = 22.36


de (L):(12.5 to 33% of Distance L)

11.25 nm


de (R):(12.5 to 33% of Distance R) 10.68 nm


Datum
• A datum point is established at the mid-point between the ends of the
leeway vectors
• De is the radius of the circle of probability around the datum

De
Datum

Leeway

Total Water Current

Point
Actual T
arget Dr
ift

LKP


Worksheet 1
FIX ERRORS

Distress craft error (x): (Table J.1, J.2 or J.3)

15

nm

Search craft error (y): (Table J.1, J.2 or J.3)

0.1

nm


Navigational Fix Errors

Appendix N – Probable Errors of Position
• X is the estimated error of the position of
the craft in distress
• Y is the estimated error of the position of
the search craft