Procedures for 10 Working Dives 00 SECTION PAGE SECTION PAGE 10.1 SEARCH AND RECOVERY . 10- 1 10.4 HYDROGRAPHIC SUPPORT . 10-17 10.1. 1 Circular Search . 10- 2 10.4. 1 Hazards to Navigation . 10-18 10.1. 2 Line-Tended (Fishtail) Search . 10- 3 10.4. 2 Locating and Measuring Least 10.1. 3 Jackstay Search Pattern . 10- 5 Depths . 10-18 10.1. 4 Searching a Large Area. 10- 5 10.4. 3 Resolving Sounding 10.1. 5 Tow Diving. 10- 5 Discrepancies . 10-18 10.1. 6 Drift Diving . 10- 7 10.5 WIRE DRAGGING . 10-18 10.1. 7 Deepwater Towbar Search . 10- 8 10.6 UNDERWATER TOOLS . 10-19 10.1. 8 Cable Cross Search . 10-10 10.6. 1 Hand Tools . 10-19 10.1. 9 Search Without Lines. 10-12 10.6. 2 Pneumatic Tools . 10-19 10.1.10 Recovery . 10-12 10.6. 3 Hydraulic Tools . 10-20 10.2 UNDERWATER NAVIGATION. 10-12 10.6. 4 Electric Tools . 10-21 10.2. 1 Basic Underwater Navigation . 10-14 10.6. 5 Power Velocity Tools . 10-21 10.2. 2 Water Depth/Underwater 10.6. 6 Cutting and Welding Tools. 10-22 Distance . 10-15 10.7 MAINTENANCE AND REPAIR 10.2. 3 Diver Navigation Board . 10-15 10.2. 4 Precision Underwater Navigation . 10-15 TASKS . 10-23 10.2. 5 Choosing and Converting Between 10.8 SALVAGE . 10-23 Coordinate Systems . 10-15 10.8. 1 Lifting Methods. 10-24 10.2. 6 Post-Mission or Real-Time 10.8.1.1 Dead Lifting . 10-24 Coordinate System Conversions . 10-16 10.8.1.2 Internal Buoyancy Lifts. 10-24 10.2. 7 Installation . 10-16 10.8.1.3 External Lift Bags . 10-25 10.2. 8 Environmental Variables . 10-16 10.8.1.4 Air Lifts . 10-27 10.2. 9 Raw Position Data. 10-16 10.9 UNDERWATER DEMOLITION AND 10.2.10 Quality Control . 10-16 EXPLOSIVES . 10-27 10.3 INSTRUMENT IMPLANTATION . 10-16 10.9. 1 Types of Explosives . 10-28 Procedures for Working Dives 10 10.1 SEARCH AND RECOVERY where All search techniques rely on one common element: r = radius the adoption and execution of a defined search pattern. k = safety factor (between 0 .1 and 1.5) The pattern should commence at a known point, cover a C = total probable error known area, and terminate at a known end point. Search patterns are implemented by carrying out The total probable error is a mathematical combination search sweeps that overlap. To be efficient, the overlap of the initial error of the object's position (x), the navigation should be minimal. The initial step in a search is to define error of the search craft (y), and the drift error (de). The the general area and the limits to be searched. If the drift error is assumed to be one-eighth of the total drift. search is being conducted to locate a specific object, the The total probable error, (C), is: last known position of the object is the starting point for defining the search area. The drift in the open sea result- C = (de2+x2+y2)1/2 ing from sea and wind currents, the local wind condition at the time the object was lost, and the leeway (movement Each factor included in the total probable error is through the water from the force of the wind) should be somewhat subjective. Selecting conservative values has studied. Sea currents can be estimated for a particular the effect of enlarging the search radius; sometimes, a area using current NOAA Tidal Current Tables and Tidal small search radius is selected and repeated expansions Current Charts and the U.S. Navy Current Atlas of Sur- are made around the datum point until the object is locat- face Currents. Wind currents can be estimated using ed. Searching the area around the datum point can be Table 10.1. implemented using a variety of patterns, depending on the The leeway generally is calculated at zero to ten per- search equipment, visibility, or number of search vehicles cent of the wind speed, depending on the area of the object involved. exposed to the wind and the relative resistance of the Systematic searching is the key to success. A good object to sinking. The direction of leeway is downwind, search technique ensures complete coverage of the area, except for boats that have a tendency to drift up to 40 per- cent off the wind vector. Calculation of the value and direction of leeway is highly subjective for objects that float TABLE 10.1 or resist sinking; however, if the average wind velocity is Wind Speed and Current Estimations relatively low (under five knots [2.5 m/s]), or the object is heavy enough to sink rapidly, the leeway has little or no Wind Speed, Wind Current, effect on the calculation of a probable location. knots (m/s) miles/day (km) After the vectors of water current, wind current, and leeway have been added and applied to the last known 1 Ð 3 (0.5Ð 1.5) 2 (3.2) position of the object, a datum point is defined. The datum 4 Ð 6 (2.0Ð 3.0) 4 (6.4) point is the most probable position of the object. Once the 7 Ð10 (3.5Ð 5.0) 7 (11.3) datum point has been defined, the search radius around the 11Ð16 (5.5Ð 8.0) 11 (17.7) datum point is selected. The search radius, (r), is equal to 17Ð21 (8.5Ð10.5) 16 (25.8) the total probable error of position plus a safety factor, as 22Ð27 (11.0Ð13.5) 21 (33.9) defined by the following formula: 28Ð33 (14.0Ð16.5) 26 (41.9) r = (1 + k) C 10-1 clearly defines areas already searched, and identifies areas Descending Line remaining to be searched. The visibility, bottom topogra- phy, number of available divers, and size of the object(s) to be located are prime factors in selecting the best method for Current a particular search. There are two acoustic approaches to underwater Marker Line object location. The first is to traverse the area being searched with a narrow beam fathometer, keeping track of Weight the ship's position by normal surface survey methods. This approach is suitable for returning to the position of a First Search Circle known object that has high acoustic relief and is located in Search Line Descending Line Anchor an otherwise relatively flat area, such as a wreck, signifi- Second Search Circle cant rock outcrop, or a mount. The second acoustic method involves the use of side-scan sonar. When using side-scan sonar, a transponder receiver unit is towed from FIGURE 10.1 the surface. Acoustic beams are broadcast left and right, Circular Search Pattern and the signals received are processed to present a picture of the bottom on both sides of the transponder-receiver unit. Approximate object position can be determined by can be used to assign precise distances. The divers hold the knowing the ship's position, heading, and speed, and the search line and swim in a circle until they return to the approximate position of the transponder-receiver unit with marker line, which ensures that a full 360 degrees has been respect to the ship. covered. The divers increase the radius for the next search, Onboard microprocessors to control the range/gain moving out a distance that permits good visual coverage. necessary to produce optimum display contrast are begin- This procedure is continued until the outermost perimeter is ning to replace manual adjustment of the gain; the use of reached (see Figure 10.1). microprocessors simplifies the task of the observer and When two divers are searching, search effectiveness increases the effectiveness of a search. If more precise can be increased by having one diver hold the circling line determination is necessary, one of the acoustic surveying taut and swim the outside perimeter of the area to be methods can be used. Underwater object location using searched while another diver sweeps back and forth along acoustic techniques involves divers only after the object has the taut circling line. As shown in Figure 10.1, the first been detected. The following diver search techniques have search will cover a full circle bounded by the outside diver's been useful for such applications. path. The search starts and finishes at the marker line. The search may be extended by the pattern, in which case the 10.1.1 Circular Search circling line is marked at the point where the outside diver In conditions where the bottom is free of projections, was previously stationed. The outside diver then moves to a the visibility is good, the object to be located is reason- new position, farther out on the circling line, and the inside ably large, and the area to be searched is small, use of the diver sweeps back and forth between the marker and the circular search technique is recommended. Under such outside diver's new position. Positions may be changed at favorable conditions, a floating search line is anchored to regular intervals if the divers become fatigued. Changing the bottom or tied with a bowline around the bottom of positions can be done at the end of each sweep by having the descent line and is used to sweep the area. To deter- the outside diver hold position after moving out one visibili- mine when a 360-degree circle has been made, a marker ty length; the other diver then moves outside, taking up his line should also be laid out from the same anchor as the position for the next sweep.