PATENTS. 



619 



is most needed. The revolving jet shaft, 

 on the contrary, will, it is thought, constantly 



JET PROPULSION. 



deliver its strokes against comparatively solid 

 water. 



Wreck Buoy. Among new maritime appli- 

 ances is one that should commend itself at least 

 to all shipping merchants and insurance compa- 

 nies, if not to mariners. It is, in brief, a properly 

 marked float attached to a long, fine wire or line, 

 and covered by a box, which may serve as a deck 

 seat or other piece of ship furniture. This box is 

 a fixture so long as the ship is afloat, but it is held 

 together with glue, which dissolves after a short 

 period of submergence and liberates the float, 

 which rises to the surface and remains anchored 

 by its line, giving notice to passing vessels that a 

 disaster has occurred, and locating the position of 

 the wreck. Such a device, if it had been in gen- 

 eral use, would no doubt have cleared up many 

 mysteries of the sea that must now remain for- 

 ever unsolved. 



Marine Sentry. This useful invention con- 

 sists of a trough-shaped float so attached to a 



wire or line that 

 it will dive to any 

 depth not exceed- 

 ing forty-five fath- 

 oms when towed 

 through the water. 

 (See lower illustra- 

 tion. At its for- 

 ward end is a trig- 

 ger, which on 

 touching bottom 

 disengages the for- 

 ward sling of the 

 towing line, suf- 

 fering the float to 

 rise to the surface. 

 The diminished 

 pressure strikes a 

 pong on board the 

 ship, announcing 

 whatever depth of 

 water the sentry 

 has been set to 

 report. The upper 

 part of the engraving shows the sentry in the 

 three positions of towing free (at the left), touch- 

 ing bottom (middle), released and rising (right). 

 Stern-Wheel Propulsion. The superiority 

 in many respects of stern wheels over side wheels 

 for steamboats has long been recofjnized. This 

 is partly due to what is known as the " following 

 wave " that is to say, the wave formed by water 



MARINE RENTRV. 



rising up just after it has passed under the mov- 

 ing vessel. In the case of a stern-wheeler th< 

 best results are attained when the paddles re- 

 volve just in the crest of this wave, the fluid par- 

 ticles of which are actually in motion in the same 

 direction as that in which the vessel is moving. 

 Mr. Yarrow, the distinguished English builder, 

 has made some interesting experiments in this 

 direction. The principal fault of the strn wheel 

 is that it is difficult to steer the boat. In Ameri- 

 can waters this has been overcome to some con- 

 siderable extent by using what is known as a re- 

 cessed wheel, double rudders being employed, 

 one on each side of the wheel. Boats of this 

 character are extensively used in our Southern 

 rivers, but they do not appear to be known abroad. 

 To meet the difficulties mentioned, Mr. Kincaid, 

 of Glasgow, has devised an engine and paddle- 

 wheel which are made to revolve in trunnions, 

 and by means of proper gear the paddle-wheel 

 can be immersed to a depth representing the 

 greatest efficiency. The whole bed plate, en- 

 gine, wheel and all, revolves on a pivot in a 

 horizontal direction, so that the wheel can be 

 moved through an angle of 15 on each side of 

 the center line of the vessel ; thus are the rudders 

 done away with altogether, and the steering is 

 effected by means of the propulsive apparatus. 

 The attention of English engineers has been 

 drawn to this type of vessel from the necessity 

 of employing shallow-draft boats in navigating 

 the rivers of Africa. 



Screw Propellers. At least two patents have 

 been taken out during the year which bear a 



PERFORATED PROPELLER. 



striking resemblance to one another. Neither the 

 general shape of the propeller blades nor their 

 pitch is essentially different from those that have 

 long been in use, but, instead of being solid, the 

 part of the blade nearest the hub is cut away so 

 that what is known to engineers as the " dead 

 water " escapes through openings in the blades, 

 and is liberated, instead of acting as a drag as in 

 the case of the ordinary propeller. It is also 

 claimed that less power will be required to drive 

 this than the ordinary type of propeller, and that 

 there will be decidedly less vibration of hull and 

 machinery. Daniel H. Welch, of Astoria, Ore- 

 gon, and Charles Myers, of Manchester, England, 

 are the patentees. 



Hydrophone. Such is the name given by its 

 inventor, Capt. McEvoy, late of the Confederate 

 service, to a device for detecting the approach of 

 hostile vessels. The idea is to sink electrically 

 connected instruments off shore, each being pro- 

 vided with a sensitive vibrator. No screw-driven 

 vessel can pass within a mile of this without giv- 

 ing notice of its presence. A series of successful 

 experiments has lately been conducted at Stokes 

 Bay in the presence of a committee of English 



