﻿Stewart. — On Foundation of Lighthouse in Ponui Passage. 1 37 



required the best efforts of four men about ten minutes to penetrate, wliich 

 being eifected, a further depth of twenty feet was easily done in about two 

 minutes more. The crust was, in these trials, estimated at a thickness of four 

 inches. 



A temporary platform having been built on the site, the screwing down 

 was effected by fitting a strong capstan embracing the body of the pile, which 

 was moved upwards a few feet at a time as the pile descended. This capstan 

 was nineteen feefc in diameter over the ends of the bars, which were fitted so 

 that a rope could encircle them, as round a drum. An ordinary single and 

 double power winch was placed in a convenient position, and the power trans- 

 mitted to the capstan by an endless rope coiled three times round the winch 

 barrel, and twice round the capstan bars ; the slack was usually taken up by 

 hand. The pile could be, and usually was, screwed down about five feet, 

 before fleeting the capstan up another lift. The winch was usually placed in 

 single gear, and with this four men could work easily, making twenty-eight 

 revolutions of the handles per minute. The ratios of the winch handles and 

 radius of the barrel, and of the single gearing compounded, show that a force 

 on the handles is increased a little over twenty-five times at the circumference 

 of the barrel. Hence four men at the handles were equal to 100 exerting 

 the same force at the ends of the capstan bars. The circumference of the 

 capstan was sixty feet, and it revolved at the rate of ten feet per minute, or 

 one turn in six minutes. As the average descent of the screw was three inches 

 per revolution, its rate was thus one half inch per minute, requiring for actually 

 screwing the full depth of twenty feet, a period of eight hours. A man's power, 

 working at a winch eight hours per day, is usually taken at 2,000 foot pounds 

 per minute, but as the men in this case never worked more than from one to 

 two hours without stopping, and adjusting the capstan, or other parts, and 

 rests often occurred, we may take the power exerted at 3,000 foot pounds. 

 The circumference of the path of the handles being 8-6 feet, twenty -eight 

 revolutions per minute give 240-8 feet, by which dividing 3,000, we have nearly 

 thirteen pounds as continuous pressure exerted by the hands. This again is 

 equal to (with foiir men) l,300ft)S. at the capstan rope, moving ten feet per 

 minute, and as each foot required twenty-four minutes to screw down, it 

 follows that it was also attained after an expenditure of 312,000 minute foot 

 pounds, or a force equal to raising 139 tons one foot high had to be exerted to 

 screw the piles down one foot. The slip is stated at an average of three inches 

 per revolution, being 50 per cent, of the pitch. The actual descent was about 

 two and a half inches at the beginning, one and three-quarter inches in passing 

 through the crust, and from three inches to five in the mud, for each 

 revolution. 



The total weight of the structure is about sixty tons ; tliis is mainly sup- 



