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EQUIPMENT AND INSTRUMENTS 



4624 



4624. Ship Sounding Chair 



A sounding chair (also sometimes called the chains) is an elevated platform on 

 which the leadsman stands when taking a handlead sounding. A ship sounding chair 

 should have the following characteristics: 



(a) It should be located well forward of amidships, preferably near the bridge. The leadline can 

 be heaved better from this location, and it permits the leadsman, recorder, and observers to be 

 stationed near one another. 



(b) It should extend over the water far enough to ensure that the lead, when swung in taking 

 a sounding, will be well clear of the side of the ship. 



(c) It should be at least 18 or 20 feet above the water, if practicable, so that a leadline with a 

 toggle attached at the 18-foot mark will not strike the water, when swung. 



(d) The platform of the chair should be sturdy and well braced. If formed of a grating, the 

 openings must be small enough so that the leadsman's shoe cannot possibly catch in them. The edge 

 of the platform must be arranged so that the leadsman cannot accidently step off it. 



(e) The sides of the sounding chair should be about 3 feet high, padded around the top to provide 

 the leadsman with something to brace himself against, and covered with canvas to protect the leadsman 

 froin the spray from the leadline. 



(/) The chair should be demountable so that it may be removed, or swung inboard, to be out of 

 the way in docking the vessel. 



(g) A survey ship should have two sounding chairs, 

 one on each side, for the use of right- and left-handed 

 leadsmen, and when soundings need to be taken so 

 rapidly as to require two leadsmen simultaneously. 



4625. Launch Sounding Chair 



A sounding chair for use on a hydrographic 

 launch should have the same general charac- 

 teristics as a ship sounding chair, except that 

 it should be proportionally smaller and lighter 

 for a small launch. The principal difficulty 

 on a launch is to obtain sufficient elevation 

 for the swing of the lead. On a launch with 

 a decldiouse this can be attained by extending 

 the platform from the top of the deckhouse 

 and bracing it against the side of the hull or 

 the guardrail. Vertical soundings in depths 

 of 15 to 20 fathoms can be obtained from an 

 installation of this type at regular sounding 

 speed. 



For temporary use on a small launch, a 

 standard 55-gallon oil or gasoline drum, 

 secured to the gunwale or bulwark, makes a 

 satisfactory sounding chair, easily and quickly 

 installed. It is especially satisfactory for 

 sounding in depths of water less than 8 or 10 

 fathoms. The top is cut away and the inboard 

 side of the drum is cut down to afford easy 

 entrance and exit. A length of ordinary gar- 

 den hose, split open, should be secured over the upper edge to protect the leadsman. 

 For a whaleboat a satisfactory sounding chair can be provided by a small platform 

 built of 2- by 4-inch lumber, which is laid across the gunwales of the boat just aft of the 



Hiding chair extended from top of deckhouse. 



