i?6 HARBOUR CONSTRUCTION. 



the framework with rubble as quickly as possible, because upon 

 this the stability of the structure in a great measure depends ; 

 and frames, while unbacked, are very liable to be displaced and 

 damaged, even by moderate seas. 



The function of the timber-framing is to encase the rubble 

 and prevent its dispersion, the rubble, in its turn, giving 

 support to the framing by its weight. 



The larger stones, selected for the faces, are usually packed 

 in their rough undressed state, so as to form fairly close work, 

 the largest, as a matter of course, being reserved for the weather 

 side. The hearting is usually formed by merely tipping the 

 rubble from waggons. 



Some years ago, acting under the late Sir John Coode's 

 instructions, I removed one of these breakwaters, which was 

 constructed between the years 1856 to 1865. It was 1300 feet 

 in length, and originally extended into water having a depth of 

 23 feet at L.W.O.S.T. It was exposed to heavy seas, which it 

 withstood remarkably well. Unfortunately, it was so placed as 

 to act the part of a groyne, and cause considerable shoaling ; 

 hence the necessity for its removal. 



The ties and braces in this structure were formed of double- 

 headed iron rails, weighing about 84 Ibs. per lineal yard, and 

 they passed completely through the work. Similar rails were 

 also used as outer walings. 



After a lapse of about twenty- three years, although the rails 

 were thickly encrusted with rust, they^were quite sound, and had 

 lost very little of their weight. 



The piles of this breakwater were of ironwood, and were for 

 the most part completely eaten through by sea-worms at about 

 the level of low water of neap tides. Notwithstanding this, the 

 rail ties, above and below that level, held the frame timbers 

 together so well that the upper portion of the framework re- 

 mained like a cap placed over the rubble. 



The methods adopted for repairing breakwaters of this 

 description necessarily vary under different conditions. If the 

 nature of the bottom will admit of it, the driving of an outer 

 row of piles is sometimes resorted to. 



In some cases, when the piles have decayed, the structures 

 have been encased with concrete blocks. In other instances the 

 timber- work has been renewed pile by pile, or piece by piece, 

 as it became decayed. 



