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Search And Rescue Toolkit |
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General Search Considerations
The coastal SAR planning model described here is used to facilitate ease of determining a search area and a rapid deployment of search assets into a search area. Although it is ideally used when the response is mounted less than six (6) hours from the time of distress the principles can also be applied for up to 24 hours after this time by drifting the datum as described in the section headed Recomputed Datum. This provides the SMC with a tool to rapidly determine a search area. The oceanic model incorporating leeway divergence and solving for total probable error should be used for all situations in excess of 24 hours or when time and unit availability allows
Calculating Drift
Use the above two interactive maps to obtain current and wind conditions offshore. This information can be used when calculating the drift of an object in the water. To work out the drift of an object, work out how long the object would be in the water before the vessel arrives on scene. Example: If a life raft is drifting for 2 hours and the rescue vessel will take approx 1.5 hours to reach the location, then drift of 3.5 hours should be applied. To work out an EP (Estimated Position) of a target, you need to know the following:
To work out drift, using a chart, plot the last known position. Plot a vector based on current. All objects drift with current in the same way, if the current s flowing at 0.6 KNOTS to the SOUTH, then plot a vector at 180 degrees from the LKP. The distance should be 0.6 x time (in hours). Next plot a drift vector based on wind effect on the target. To establish this, use the LEEWAY table from the NATSAR manual. You will need the "multiplier" and "modifier" for the target and insert in this equation: Leeway Speed (knots) = [Multiplier x Wind Speed (knots)] ± Modifier
Want to know more about the classification in the above table? Click here to see information about each of the leeway drift objects in Table D-5:1 Multiply this value by the amount of hours target has been drifting. Apply the wind vector using the direction available on the map above, on the tail end of the current vector. Join the LKP to the tail end of the wind vector. This line reveals the TOTAL DRIFT VECTOR and establishes an EP. Search should be conducted by first going to the LKP, running down the drift line to the EP. If target is not located, establish a search pattern with the center of the search at the EP. The EP becomes known as the SEARCH DATUM.
Divergence
When a search object first begins to drift, the wind will push the object in a downwind direction. As the search object continues to drift, the wind will cause the search object to deflect (or diverge) to either the left or to the right of the downwind direction. The amount of divergence is dependent upon the shape of the exposed flat-plane area of the search object. Divergence is caused by the lack of symmetry of the drift object. When directional uncertainty applies, the divergence angle is both added and subtracted to the downwind direction to account for the search object's divergence to the left or right of the downwind direction. Thus, the formula to determine the direction of the divergence is:
Search Area
A great number of maritime search and rescue incidents occur within 25 NM of the coast, in under 300 metres of water. The coastal search-planning model is to assist with a rapid response and should ideally be used when the report of a craft in distress is notified to a SAR authority within six (6) hours of the actual distress situation arising. In most cases, considering the short response time to coastal SAR incidents, if the search asset proceeds to the Last Known Position (LKP) or Splash Point (SP) of the craft in distress it will be found. However, the craft in distress may not be in sight because of inaccuracies in the initial position reported; inherent errors associated with drift factors; and/or errors in the navigation of the search asset. If the time since the craft became distressed is less than four (4) hours and it is not located at the SP (splash point), draw a 6 NM radius centred at the SEARCH DATUM. Then draw a square search area with the sides tangential to the circle. This will give a search area of 144 NM² The purpose of drawing a radius around the datum is to describe the geographical area most likely to contain the search object. This area already contains the total Probable Error (E), which includes the Initial Position Error (X) of the distressed craft and the Navigation Error of the SRU (Y), but does not include Drift Error (De). If the time since the craft became distressed is more than (6) hours increase search area to 8 NM radius centred at the SEARCH DATUM after applying drift. Then draw a square search area with the sides tangential to the circle, and in line with the drift vector. This will give a search area of 256 NM² 
Including LKP
If the LKP (Last Known Position) or SP (Splash Point) is outside the search area, then the area should be boxed in and included in the search area 
Position Uncertainty
If the position of the LKP (Last Known Position) or SP (Splash Point) is in question, calculate a datum for each position (LKP 1 and LKP 2) and draw a six (6) NM circle around each and enclose the circles (Figure 3-19). This could be the case for a vessel in transit down the coast. The vessel may have a last contact point and then immediately came in to distress or traveled along its course until the present time, and then came in to distress. The search Datum can be assumed as a point midway between the two individually calculated Data. If extreme distances separate the positions in doubt, consideration should be given to treating them as separate vessel adrift incidents. 
Track spacing (distance vessels are apart) are based on conditions and target type.
Tables in the NATSAR manual show maximum distances vessels should be apart
(or distance between tracks of a single search vessel). Track spacing distances are listed in Nautical Miles.
Note: sailboat is only considered a sailboat if sails are up. If sails are not up (or unknown if they are up)
use the sweep width value for a powerboat of the same size
Obtain the figure for visibility from the AIRPORT OBSERVATIONS table below
Based on conditions, the Track spacing is reduced by the factor in the table below.
Track spacing is further reduced when fatigue is a factor in the search.
This is fatigue of the vessel crews in the search. In good conditions, fatigue would be a factor after eight hours of searching for a target.
However in bad conditions, fatigue may be considered after only a few hours of searching in large seas.
To work out the Total Track spacing based on all factors, use the formula:
Track Spacing =(Uncorrected Visual Sweep Width) x (Weather Correction Factor) x (Fatigue Correction Factor)
The probability of detection table shows, based on sweep with and number of search patterns performed, the probability of detecting a search object in %
Click here to access the full NATSAR manual and other S.A.R. tools below
Taxonomy Class Definitions/Descriptions
The following section provides information about each of the leeway drift objects in Table D-5:1. For each description, the target characteristics are summarised but descriptions are in no way meant to be all-inclusive. They are intended to assist a search planner in target identification. Proper identification will make the application of more specific leeway values possible. Some categories in Table D-5:1 do not require further explanation and therefore further descriptions are not included. The SAR planner should also be reminded that any classification system will have overlap between some categories. In these cases, a decision must be made about the most probable situation. a) Person-in-Water (PIW) b) Persons in the water including persons without any floatation, and those with a throwable cushion, with a PFD, in an anti-exposure suit and in survival/immersion suits
c) Maritime Survival Craft This section includes life rafts, lifeboats, and life capsules as illustrated at Figure D-5:2. It does not include dinghies or inflatable boats that may be carried for the same purpose.
d) Other Maritime Survival Craft
e) Aviation Life Rafts Fall basically into two groups, life rafts and slide rafts. Aviation life rafts are similar to marine life rafts, but are usually made from lighter materials.
f) Person-Powered Craft This description includes all forms of rowed or paddled boats including rowboats, inflatable boats without motors, canoes, kayaks, stand up paddle boards, surfboards and windsurfers. For examples, see Figure D-5:3. f) Mono-hull Sailing Vessel It is assumed that all targets in this category are adrift; therefore sails are down or missing and the crew is unable to manoeuvre the vessel at all. A class of small to medium sized sailing vessels generally less than 20 ft and never more than 30 ft in length, they are typically designed for a single purpose such as racing or day sailing.
g) Skiffs Open boats less than 20 ft long that use an outboard motor as the primary source of propulsion. Some have characteristics identical to rowed boats with the exception that an outboard motor has been attached to the stern. This group includes, but is not limited to, tenders for larger vessels, bass boats, hunting boats, Jon boats, and a large category of utility boats. Skiffs are usually found on lakes and rivers, but are also common in the calm waters of many bays and rivers that provide access to the open ocean. h) Personal Water Craft Include a number of different designs for one or more persons. Generally there are stand up models and ride on models. Some craft marketed as PWC closely resemble small sport boats. Most PWC's have water jet propulsion. No leeway drift experiments have yet been performed on PWC's and they do not appear within Table D-5-1. Leeway category choice should be based on number of passengers/loading, size of PWC (draft, length, freeboard) of PWC. These factors may be comparable (not exactly) to several other leeway targets. i) Sport Boats Includes pleasure craft from 15 to 28 feet long with beamwidths from roughly 6 to 9 feet. They include metal, fibreglass, and wood vessels with a V, modified-V, or deep-V hull form. Sport boats can be outfitted with inboard, outboard, or I/O propulsion. This category includes side console (closed bow and bow riders) and cuddy cabin boats. (Figure D-5:8) j) Sport Fisher Include pleasure and commercial craft from 17 to approximately 100 feet long with beam widths up to 24 ft. The majority are between 30 and 50 ft long, with beam widths between 10 and 15 ft. This class includes both semi-displacement and planning hull forms that can be outfitted with inboard, outboard, or I/O propulsion. This category includes boats with simple centre console or walk-round cabin. Convertibles are sport fishers with a walk around cabin and flying bridge. Convertibles designed for offshore fishing may also have a spotting tower. Many convertibles provide extended cruising capabilities similar to sport cruisers, but their after deck design provides a larger open area to work fishing gear. Some of these vessels can also be found in the cruiser or motor yacht categories. (Figure D-5:9) k) Commercial Fishing Vessels Include vessels from 45 to 100 feet long designed for fishing or shell fishing in coastal and ocean waters. They include side and stern trawling rigs, long liners, bottom dragging rigs, and purse seiners. Pole fishers are simply modified use of a sport fisher or sport cruiser and should be treated as such. Commercial fishers can be working alone, as paired vessels, or can be the mother ship to a group of smaller fishing skiffs. These vessels have different design features based on their purpose, but all have some form of deckhouse and an open area from which nets can lines are worked. A deck winch and boom system is commonly used to handle nets or lines. (Figure D-5:10) l) Coastal Freighter Include a wide range of commercial shipping platforms up to 100 feet in length. These vessels transfer cargo from one port to another, and shipping agents can provide estimated voyage schedules. Coastal freighters include vessels with a deckhouse on the forecastle, a midships deckhouse (common to cargo vessels), and an aft deckhouse (common to tankers and container ships). Leeway of these vessels will of course not only vary with respect to deckhouse location; it will also be greatly affected by loading, amount, and type of cargo. (Figure D-5:11) m) Boating Debris Includes any debris that can be expected from a boat that is sinking and/or breaking up. It may include paper or plastic containers, bedding or clothing, and a variety of fragmented boat sections.
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