THE EVOLUTION OF THE LIGHTSHIP. 107 



pose each must be made the subject of special study with reference to a moored 

 vessel. During the past few years, Mr. George Idle has made many observations 

 and experiments on the rolling of Irish lightships. In papers read before the 

 Scientific Society of Ireland in 191 1, and the Institution of Naval Architects of 

 London, in 19 12, he gives much valuable information on the forms and effects of 

 bilge keels for lightships. He finds that properly designed and located bilge keels 

 are of the greatest value in reducing both the amplitude and period of roll; and 

 the results of his work appear to show that they are an economical and convenient 

 means of obtaining the greatest results for the smallest expenditures. It is scarcely 

 necessary to say, however, that bilge keels alone cannot make an ideal light 

 platform of a vessel, and that the vessel of the future will include each element of 

 design developed as Mr. Idle has developed the bilge keel, and in this work I shall 

 endeavor to play a part. 



In the more practical features of design the same effort for improvement 

 has been continued. These early lightships were built of wood, and some of them 

 staunchly built. The English lightship at the Nore, built of oak and ash in 1804, 

 was examined by Mr. Idle in 1889 and found to be in excellent condition. The 

 U. S. lightship on Bush Bluff Station dates from 1849, and its oak is sound and hard 

 and should be good for many years. These ships, however, are exceptions to the 

 general rule. In 1856 the Fifth Auditor of the U. S. Treasury, in a report on the 

 lighting service, states that the average life of a wooden lightship, as then built, is 

 only five to ten years, with heavy annual cost for upkeep and repairs. 



The first marked practical improvement in hull construction was the substi- 

 tution of iron and steel for wood. 



Iron was used as a structural material for shipbuilding purposes at an early 

 date. In 1843 the Trinity House discussed and rejected its use for their lightships 

 and it was not until 1857 that they adopted it in a vessel built for service on the 

 Goodwin Sands. The Mersey Dock Board, however, was more progressive, and 

 the first iron lightship appears to be that stationed by them on the North West 

 Shoal below Liverpool in 1845. The vessel was 98 feet long and normally drew 

 8 feet 6 inches. Its tonnage was 203. The hull was subdivided by three water- 

 tight bulkheads, and fitted with a deep bar keel, and two bilge keels on each side. 

 Three lights were carried at different elevations, and a lattice daymark was fitted 

 on the mainmast. Notwithstanding the highly satisfactory performance of this 

 vessel, many objections were made to the use of iron. It was feared that they 

 could not be made strong enough to withstand the shocks received by a vessel at 

 anchor in a rough sea; that they would suffer more severe damage than a wooden 

 hull if driven ashore; that the interior of the hull would sweat and become damp 

 and unwh6lesome ; that its cost would be prohibitive ; and that the bottom would 

 foul very rapidly. In all but the last, experience has ultimately proved the oppo- 

 site to be the case, but the wooden lightship continued in general use for many 

 years. 



The advantages of iron as a structural material, however, were being con- 



