44 "Thomas Stevenson, Esq., on Harbour Screw-Cramps. 
or in connecting them together with oaken tree-nails. The 
great advantage, therefore, of any contrivance which could be 
easily, and, above all, quickly applied for this purpose, with- 
out involving the expense of jumping holes or cutting the 
stones, appears very evident. The adoption of such means 
might confidently be expected, to a great extent, to prevent 
those great losses to which almost all such works are 
more or less liable during construction, and of which I 
have given a few examples. The importance of the subject, 
more especially at this time when the English refuge har- 
bours, involving the expenditure of so many hundreds of 
thousands of pounds of the public money, have been at length 
commenced in good earnest, must be my excuse for bringing 
an untried project before this Society. 
The accompanying drawings and models(Plate II.) represent 
two simpleimplements, which, from their resemblance to others 
commonly used in carpentry, may be termed Harbour Screw- 
Cramps. They are intended to be employed for temporary 
use in the construction of harbour and other sea works in 
exposed situations. The principle on which these have been 
designed, is that of coupling stones together in such a man- 
ner that the outermost cannot be removed without dragging 
the adjoining stones along with it. That represented by the 
diagrams, marked figs. 1, 2, and 3, is a screw-cramp adapted 
for a vertical or nearly vertical sea-wall. It consists of a 
cross rod of iron a, inserted diagonally between two of the 
stones of the work, and on either end of this rod, iron rods 
or chains 6, are slipped, one set being at the front of the 
wall, and the other at the back. To prevent; the backing of 
the wall from pressing upon the chains or rods, a small void 
like a drain, three inches square, is to be formed at the back of 
the wall as the work proceeds. At the conclusion of each 
tide’s work, the abutment-plate c, is placed diagonally across 
the last stone, and the chains or bars are tightened up by 
means of the capstan-headed screws d, when the whole is 
thus bound together, and rendered secure. When the work 
is again commenced, the abutment-plate c, is removed, and 
more stones are set, which are, in like manner, connected 
with the others at the end of the tide’s work by lengthening 
