SCREW PILE JETTIES.

Timaru Herald, Volume II, Issue 64, 5 August 1865, Page 7

SCREW PILE JETTIES.

The following communication from the Super- j intendent of Marine at Madras to R. Greaves, | Esq. , of Akaroa, was unavoidably crowded out j of our last issue. We feel assured, however, I that it will be read with considerable interest liere : — Madras, April 27, ISGS. . Sir, — Your letter to the Master Attendant of Madras, of the 14th November, 1863, was put into my hands on my return from England, with an intimation that it had not been replied to. I regret it should have been left so long unnoticed, but I will now proceed i& afford you such information as my limited experience will permit. You are desirous of learning how our screwpile pier answers the purposes for which it was constructed, with a view to the erection of one or more m New Zealand. The port of Madras is a perfectly open roadstead, where ships anchor at one-half to one mile off shore, m 6 to 8 or 9 fathoms water, good holding ground. A heavy surf breaks along the whole length of the coast, sometimes as far out as 2-4 to 3 fathoms water, but more usually iv Bto 10 feet. No boat of European build can pass this surf with safety, and very large unwieldly craft are used, the planks and timbers of which are sewn together. Even these carry but two tons, and are frequently swamped, and it was to overcome the difficulties thus attending shipping operations, that the pier was proposed having a certain amount of wharfage outside the surf. The sand along ©nr coast accumulating very rapidly when any obstacle is presented, it was therefore useless to erect a solid pier, for this would only have had the effect of throwing the beach lino farther out. An open one on iron piles, 1000 feet long and 20 broad, with a T head 160 feet long and of similar breadth on the stem was therefore constructed. The piles are placed JO feet apart, the inner two rows being G inches, the outer two, 8 inches m diameter. They are screwed into the bottom from 5 to 15 feet deep, and the platform or deck is 15 feet above the level of high water. The pier commences at the beach, and runs out into 26 feet water. About 200 feet from the outer end we have eighteen feet water ; and from this outwards boats can lie alongside to load or discharge cargo. These operations are effected by cranes (travelling and standing), and trucks are used on the four lines of rail, with which the pier is furnished, for conveying cargo over it. No vessel ever attempts to lie alongside the pier, although there are some days when this could be done; but there is generally a ground swell at Madras, which would render such an attempt hazardous, not only to the ship but to the pier itself. It must, therefore, be considered simply as a boat pier, and, as this, it is a decided success. Few accidents occur at this pier, and none that are specially attributable to it. Ships' boats can communicate by it with the shore, and great advantages are derived from the ability to lift or lower heavy weights, such as boilers, guns, machinery, &c. , which required much labour and expense when passing through the surf. The whole expense of this pier will be about £115,000 ; but it is our first attempt at anything of the soi*t, and, as usual, more money was spent than necessary. Since it was commenced, I have visited England, and examined some of the piers lately put up, and T am convinced that our structure is too solid, and with too much iron m it. This certainly makes it strong ; but there are two or three attendant disadvantages. The piles being so close together and strongly braced to each other, the amount of opposition offered to the currents is so great, that sand is very considerably deposited, and the beach has extended 100 feet to seaward since its commencement. This, of course, is a very serious loss of wharfage, for the silting has more or less affected the whole length of the pier. The original cost is also greatly j increased by the large quantity of iron used, and the repairs will be proportionally augmented. My opinion is, that if clumps of piles were screwed down 56 or 60 feet apart, and connected by iron girders, sufficient strength would be afforded for nil the purposes required, less silt would be deposited, and a saving effected of nearly one half. Piers such as I describe are being built m England, 1200 to 1300 feet long, 25 feet wide, with five fathoms at high water on the outer cud, for £14,000 to £15,000. These are the sort of piers you will require for New Zealand. We have had one or two gales since the pier was completed without its suffering the least injury, and the only danger to be apprehended is from a large and strong ship drifting on it. The foregoing remarks, I think, contain all the information I can give on the subject of your inquiries, but should" you wish to have any further particulars, I shall be happy to pay attention to any communication from yourself or the Board m whose behalf you write. I remain. Sir, Your most obedient servant, ; John F. Franklin, j Supt of Marine, Madras; j To Robert Greaves, Esq. *