DYNAMIC SEARCH AREA DURING SEARCH
AND RESCUE OPERATION
Budny T.
Gdynia Maritime University, ul. Morska 81-87, 81-225 Gdynia, Poland
Abstract: In the article there are presented problems associate with determine search area during
rescue operation at sea. We compare size of the search area and search effort available which is considerably smaller. Determining of search area was based on a new model which taking into consideration local hydro-meteorological conditions. As a conclusion we proposed determining of dynamic search area as possible solutions of that problem.
1. Introduction
Search and Rescue operation is a very complicated and difficult part of work at sea. Before the SAR operation begin there have to be determined proper search area. Search area should be as small as possible and simultaneously probability of staying of searched object inside the area has to be high. Nowadays search area is determined at the beginning of the operation. For most cases it is few (two, three) hours after the disaster. The area is then searched through. Method recommended by International Maritime Organization used to determine search area allows for limit area to about 80 square nautical miles (3 hours after disaster). In most rescue operations number of rescue units is very restricted, weather conditions are bad, sea is high. It is very difficult or even impossible to search whole that area in acceptable short period of time. Time is very important factor because of the low temperature of water. Hypothermia (abnormal lowering of internal body temperature) in cold Baltic waters occurs about one hour after the survivors have been found in water. So we have to determine datum area i.e. area where it is estimated that the search object is most likely to be located, very precise. Research team from Gdynia Maritime University has worked out a method of determining search area for South Baltic which allowed obtaining significantly smaller area. That method takes into account actual speed of surface sea current at South Baltic and also dependence between speed and direction of wind and sea current direction in Polish Search and Rescue Region. There were made experiments for different types of raft to obtain their velocity caused by wind. That method not only gives smaller search
area but also datum point is determining better than in so far used methods. All further diagrams and calculates in this article are based on Gdynia Maritime University method.
2. Problem of size of the search area
Every used method doesn’t take into consideration that search area is in constant move and in constant growth. For that reason searching sometimes can be conducted inside determined area, but target can be outside that area already. It is necessary to work out a model which allow for resolving of that problem. In resolving we have to take into consideration few important factors.
In every search and rescue operation there is limited rescue unit number. Every unit has limited search effort. Search effort is the area that is possible to search during define period of time. It can be given by equation
Z = V · T · W (1)
where:
V – speed of rescue unit in knots, T – time of searching in hours, W – sweep width.
Sweep width depends on type and size of the searched object and also on hydro-meteorological conditions like visibility and sea state. It can vary from about 0.2 nautical mile for person in water to about 8 nautical miles for large raft in good visibility. Most disasters at sea happen during bad weather conditions so sweep width cannot be wider than 2 miles for big raft.
There is a problem of size of search area and available search effort which in most cases is considerably smaller. Let’s present in on example.
Search area Ws=45Kn 0,00 40,00 80,00 120,00 160,00 200,00 240,00 0 2 4 6 8 10 Tim e [h] A re a [N m ^2 ]
Fig. 1. Search area growth in time
Figure 1 shows growth of the search area determined in one hour periods for 10-person raft. Wind speed is fixed and equal 45 knots. As it can be seen on the diagram search area is growing rapidly in time. Polish SAR units in high sea state can achieve speed of about 10 knots. Sweep width for 10-person raft in bad visibility is about one and a half nautical mile. We obtain search effort equal 15 square miles per hour. On Fig. 2 there is a comparison of fixed search effort and growing search area. As we can see if the rescue unit comes to search area three hours after disaster it needs over two hours to searched off whole area. During that time the target is moving pushed by wind and current. There were made experiments to obtain dependence between wind speed and different kinds of raft velocities. Dependence of velocity of 10-person raft from wind speed (and simultaneously caused by sea surface current) is shown on Fig. 3.
3,41 1,01 0,25 0,16 0,11 0,08 0,06 0,45 0,00 1,00 2,00 3,00 4,00 0 2 4 6 8 10 Tim e [h] S E /S A r at io
0,00 0,50 1,00 1,50 2,00 2,50 3,00 3,50 10 20 30 40 50 60 70 w ind speed [Kn] ta rg et s p ee d [ K n ]
Fig. 3. Dependence of wind speed and raft speed
The possible velocity of our searched object in assign hydro-meteorological conditions is about 2,1 knots. It is obvious that we have to put rescue units exactly in the area in which the possibility of containment of searched object is the highest. For that reason we have to take into consideration velocity of searched object. It means that we have to move all available rescue units in the same direction which raft is moving in. Problem to solve is to figure out the best possible search pattern which allow to search of as large area as possible and simultaneously allow to move rescue units with the moving area. There are few search patterns recommended by International Maritime Organization i.e.: expanding square pattern, sector pattern, parallel track and creeping line. Two of them are shown on Fig. 4 and Fig. 5. In choosing of search pattern we have to take into account available speed of rescue unit, velocity of target and sweep width. Other factor which must be considered is comparison of search area and search effort. During SAR operation at the beginning search effort allows to search of whole area, but later it is impossible. Rescue unit must focus only on area with the highest possibility of target containment.
Fig. 4. Sector search pattern
Fig. 5. Parallel line search pattern
3. Solution proposal
The easiest way to solve above described problem is using helicopters. Helicopters thanks to their high speed and ability of flying and hanging are able to search whole determined area in short period of time and quickly move to another search region, if it is necessary. They are also able to take survivors aboard straight from water. But there are limiting weather conditions for using of helicopters. Permissible wind speed for “Anakonda” helicopter (used by Polish SAR services) is about 48 knots, cloud base at least 300 meters, visibility 4 kilometers (at night). Often during storm these conditions are much worse. So, we can use only surface unit in search and rescue operation. Another limit for helicopters is small number of survivors that can be taken on board. “Anakonda” helicopter can rescue only six survivors. For that reasons surface units remain basic in SAR operation.
The other possible solution of described problem is determining consecutive stationary search areas for accepted time period. For example we can determine new search area after one hour, move all units which take part in SAR operation into new area and start to search again. In this case we have to accept that there will be some parts of determined area left not searched. We have to choose only the part of the area which in the probability of containment of target is the highest. Also there is a problem of how long conduct searching in one area and when determine new one. Again we have to take into consideration drift speed of searched object, search effort available from all units and size of the determine area. Also changing hydro-meteorological conditions like wind force and direction and sea state have to be considered.
It seems possible to determine real time dynamic search area which is in constant move. Model of such area consider changing conditions and allows us to conduct searching permanently around the datum. Model of that area has to be based on actual meteorological data. All rescue units will move together with moving area which the target is most likely in. In that solution one of the basic problem is choosing proper search pattern.
4. Summary
In the article there was described a very serious problem. There is a matter of saving life of people that are in danger at sea. There is also a problem of using available rescue units in the most effective way. Further research which has to be made will be focused on resolving that problem.
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