able to mariners, but which are 

 not included in the official aids. 



LIGHT VESSELS 



All thus far mentioned are 

 known as fixed aids to navigation, 

 but it is frequently desirable to 

 put marks in the water where the 

 depth or other conditions do not 

 permit of the building of a light- 

 house or beacon. More than half 

 the aids to navigation maintained 

 by the Lighthouse Service are 

 floating — light vessels or buoys 

 moored in position. 



Light-ships are placed in loca- 

 tions off the coast, where it would 

 be impracticable or needlessly' ex- 

 pensive to build a lighthouse, and 

 they usually mark the approach 

 to a port or bay or the outer limit 

 of an offlying danger. They are 

 also sometimes used in inside 

 waters. They may be moored in 

 the channel or close to it, and they 

 have the advantage over most 

 lighthouses, that a vessel may steer 

 directly for them without danger 

 so long as collision with the light 

 vessel is avoided, and also that 

 they may be moved and moored 

 in another position when change 

 of conditions or necessity requires. 

 On the other hand, a light vessel 

 is more expensive to maintain, and 

 there is the possibility of its being 

 driven from its station, though 

 this is reduced in recent years by 

 improved vessels and moorings. 



The first light-ship, the Nore. 

 established in England in 1732, at the 

 mouth of the Thames. The first in this 

 country was stationed in 1820 in Chesa- 

 peake Bay. ofif Willoughby Spit. Sandy 

 Hook, now Ambrose, light vessel was 

 established in 1823. A light vessel was 

 placed oft' Cape Hatteras in 1824 and 

 was driven ashore in 1827. and a ship 

 was not established again in this dan- 

 gerous position until 1897, after unsuc- 

 cessful attempts had been made to build 

 a lighthouse on Diamond Shoal. 



The United States maintains light ves- 

 sels on 51 stations, and there are a num- 

 ber of relief shii)s. so that the regular 

 ships may be brought in for repairs. 

 Some of these positions are of the great- 



THE LARGEST LENS OF THE U. S. LIGHTHOUSE 

 SERVICE 



The lens is 8 ^ feet in diameter, an occulting light 

 eclipsed for 1^/2 seconds each 9 seconds. Makapuu 

 Point Light, Hawaiian Islands. 



was 



est importance to mariners, as, for ex- 

 ample, the Nantucket Shoals light vessel, 

 moored 41 miles from land, for which 

 most of the transatlantic vessels steer 

 in approaching America, and the Dia- 

 mond Shoals light vessel, moored in 30 

 fathoms of water 13 miles ofi^ Cape 

 Hatteras and marking the most danger- 

 ous locality on the .\tlantic coa.st of the 

 United States. These larger ships are 

 full-i)owered vessels, capable of return- 

 ing to their station, and they each have a 

 crew of 15. 



The latest shi]is are j^rt^vided with 

 I)owerful and distinctive lights and fog 

 signals. Thev more nearly approach the 

 lighthou.se in design, having a heavy 

 tubular iron mast surmounted by a lan- 



41 



