4452 HYDROGRAPHIC MANUAL PaGE 350 



steaming over a known distance. A new towline will stretch and it should be 

 shortened to correct lor this after havmg been used for a few hundred miles. 



When the log is streamed, the line should be payed out gradually. During use, 

 the register shall be oiled in accordance with the manufacturer's directions, which is 

 usually once every 4 hours. The rotator must be handled carefully to keep the vanes 

 from being dented or damaged in any w ay. The slightest dent in a vane will change the 

 log factor appreciably. 



When not m use, the log shall be carefully stowed in the box provided for that 

 purpose. It shall be cleaned after each period of use to remove salt deposits. 



There are also electric attachments w^hich can be used to duplicate the readings 

 of the registering dial in the pilothouse, or in any part of the vessel. This permits the 

 officer of the watch to read the log himself instead of having to rely on a quartermaster 

 or seaman who is sent aft for that purpose. 



4452. Electric Submerged Log 



The electric submerged log is installed inside the hull of the vessel with a tube 

 extending through the hull into the water. The motion of the vessel through the 

 water turns a small rotator, w^hose revolutions are transmitted to a mechanism nearby, 

 which is connected electrically to a registering dial in the pilothouse. The installa- 

 tion consists of a hull fitting and valve extension, or log casing, the submerged log 

 mechanism and rotator, the distance indicator, and the electric connections. 



Tw^o makes of submerged logs, the Chernikeef and the Meridian, are installed on 

 survey ships of the Coast and Geodetic Survey. In the most improved type of Meridian 

 log the diameter of the rotator spindle has been mcreased and the entire log tube, the 

 mechanism chamber, and the hub of the rotator have been filled with oil. The oil is 

 kept at a pressure slighth^ exceeding the external pressure to prevent the entry of salt 

 water. The dynamic pressure resulting from the ship's motion through the water is 

 utilized to drive the oil through the spindle bearings of the mechanism. A signal light 

 can be provided in the pilothouse to indicate that the oil in the log needs to be replen- 

 ished or that water has entered the mechanism chamber. The oil should be renewed 

 and the oil pressure maintained, and the mechanism should be cleaned and oiled, in 

 accordance with the manufacturer's instructions. 



The submerged mechanism should be drawn up into the hull when maneuvering 

 in shallow water, near kelp or other marine growth, where there may be submerged 

 logs, and at all times when not in actual use, to prevent fouling of, or damage to, the 

 log mechanism. An appreciable change in the log factor is an indication that the 

 apparatus may have become fouled. 



The electric submerged log possesses the following advantages: 



(a) There is no logline to be streamed, to be kept from fouling when the vessel stops, or to foul 

 on survey buoys which are passed close aboard. 



(b) There is no loss of distance when the vessel stops for vertical casts or for other reasons. 



(c) Neither the state of the sea, the speed, nor the wake of the propeller affects the registration 

 of the distances. 



(d) The log, being beneath the bottom of the vessel, is clear of all floating obstructions and 

 debris. 



(e) The apparatus can be easily drawn inboard for inspection or attention. 



(/) The registering dial is in the pilothouse where it can be read accurately and conveniently. 



