Page 263 hydrography 346 



in the "Remarks" column only when a turn is made in a line of continuous soundings 

 or when soundings are taken around the turn and recorded and their use on the smooth 

 sheet is considered necessary by the ofRcer-in-charge. (See also 3463.) Standard 

 abbreviations for these expressions are given in 8111. 



As a sounding vessel approaches the shore, or other shoal water, a lookout must be 

 kept ahead for rocks and other dangers, the helmsman and engineer must be ready to 

 carry out orders promptly, and the anglemen must be standing by to take a fix before 

 the vessel is stopped or turned. The course must not be maintained in order to obtain 

 a position on the regular interval, if there is any chance of endangering the vessel. 



Where the space between adjacent lines is less than is needed to turn the vessel 

 180°, alternate Imes should be run. The omitted lines can then be run by splitting each 

 pair of alternate lines run originally. If this is not practicable, closely spaced lines can 

 be run consecutively by making the turns in the following manner, if there is sufficient 

 sea room. When the end of the line is reached, the vessel is first turned momentarily 

 away from the direction of the desired turn and then the helm is put hard over for the 

 desired turn. The amount to tiirn in the opposite direction will naturally vary with 

 the spacing of the lines and the turning radius of the vessel. The same result can be 

 attained by turning in the following manner. For a left turn, turn 90° left and run 

 almost to the next line, then turn full right and come around 270°, easing the rudder 

 enough in the middle of the turn so the vessel will be on the desired sounding line 

 when the turn is completed. 



346. Handling the Survey Vessel While Sounding 



The methods and precautions of handling survey vessels of various sizes from the 

 largest ship to the smallest skiff are essentially the same, if allowance is made for the 

 momentum which is proportional to size. In sounding, the first and most important 

 consideration is always the safety of the vessel, and under no circumstances should a 

 large vessel be utilized to survey in dangerous waters which can be more safely navigated 

 by a smaller one. Where there is danger of grounding in examining shoal areas or 

 surveying in areas where dangerous shoals are to be expected, a slow speed should be 

 used and such work should always be performed on a rising tide, preferably just after 

 low water, in order that the vessel, if it grounds accidentally, may be more easily floated. 

 (See also 1581 and 361.) 



In handlead and wire sounding the vessel must always be maneuvered so as to 

 avoid the risk of getting the leadline or wire in the propeller (see 3421). Using echo 

 sounding the handling of the vessel becomes principally a matter of navigation and 

 seamanship. Further information on handling a vessel when it is necessary to stop to 

 obtain wire soundings is given in 3422. 



3461. Sounding Speed 



For handlead sounding from either a ship or a launch,- the maximum speed practi- 

 cable is approximately 5 Imots. When sounding in moderate depths of water from a 

 launch the average practicable speed is about 3K knots. The correct speed under any 

 conditions may be readily determined and is limited by the following two factors: 

 First, the speed must be' slow enough so that all handlead soundings are vertical ; and 

 second, it must be slow enough so that the spacing between adjacent soundings is 

 adequate for defining the profile along that sounding line. When sounding with the 

 handlead, the speed must be decreased when running with a fair current in order to 

 avoid excessively large sounding intervals and overrunning the leadline. 



