Description of a Wooden Diving-Bell employed by Mr. Rendel in the Construction of the Lary Bridge, near Plymouth.

The internal dimensions of the bell were five feet six inches in length, four feet six inches in width, and five feet in height; the sides, ends, and top, were made of two thicknesses of inch-and-half well-seasoned elm board; the inner case was constructed with its joints parallel to the top and bottom, or mouth of the bell, whilst those of the outer case were vertical, or at right angles to the inner joints; the top joints were crossed in the same manner as the sides; all the joints had a slip of flannel saturated in a composition of bees-wax laid between them, and were dovetailed together, and set as close as possible, by means of screw-clamps, &c.; the sides were rabbetted to the end, and the internal angles strengthened with brackets. The whole surface between the inner and outer case was covered with double flannel, saturated as just described, and was then connected together by a number of wooden pins dipped in tar, and tightly driven: the top was perforated with six holes, of six inches diameter each, in which were firmly fixed a corresponding number of strong lenses set in white lead; a hole of three inches diameter was made in the centre, in which was fixed a brass pipe with a screw to attach the air-tube: four hoops of wrought iron, two internal and two external,  were  screw-bolted  together, through the sides and ends of the bell; internal and external cross-lacings were also screw-bolted to those hoops, and to the sides and top of the bell; in these lacings, the chains by which the bell was suspended were fixed in strong iron eyes, which passed through the top of the bell, and were rivetted to the inner lacings. All the screw-bolts were driven with tarred oakum, and every precaution was taken to render the whole air-tight The bell, thus finished, weighed about thirty hundred weight; but it required from five to six tons and a half to sink it. and overhaul the ropes by which it was suspended : cast-iron plates, from one inch and three quarters to two inches in thickness, were therefore hung externally round its sides and ends, till it was sufficiently loaded to sink with steadiness in about twenty-five feet water. The bell was provided with two moveable seats and a foot-board for the drivers, and at top long boxes were fixed in which their tools were kept; it was provided with air by a double-acting force-pump, the cylinders of which were seven inches diameter in the clear, making a fourteen-inch stroke. This pump was generally worked by four men, and made on an average, according to the depth of the water and the run of the tide, about eight double strokes in a minute. This bell was mounted and worked upon a carriage and platform, similar to that described by Captain Savage.

(Signed)          W. DENISON,

Lieutenant, Royal Engineers.

Papers on Subjects Connected with the Duties of the Corps of Royal Engineers Vol 1. 1837

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