BREAKWATER IN PLYMOUTH SOUND

BREAKWATER IN PLYMOUTH SOUND, is a work of a similar nature to that of Cherbourg, but constructed on sounder principles, with less machinery, and fewer people. Compared in extent and dimensions with that of Cherbourg, it is only in the ratio of about one to four.

There is no port and harbour on the south-west coast of England possessing so many advantages as Plymouth,—none so well situated for assembling and equipping a fleet to watch the movements of the enemy in the harbour of Brest. Its dock-yard may be considered as the second in the kingdom in point of size, convenience, and effective strength; the margin of which stretches along the magnificent harbour of Hamoaze, a noble expanse of water, nearly land-locked, of a capacity sufficient for mooring safely a hundred sail of the line in excellent anchoring-ground, and in water that carries its depth to the very quays of the yard. On the opposite or eastern side of the Sound, and at the distance of about three miles from Hamoaze and the dock-yard, is another sheet of water, called Catwater, not quite so deep, nor so well sheltered as Hamoaze; but, since the progress made in the Breakwater, forming a safe and commodious harbour for merchant vessels of every description. These two harbours open into Plymouth Sound and Cawsand Bay, in which ships employed in the blockade of Brest, or those refitted in Hamoaze, have been accustomed to assemble and prepare for putting to sea. But the very exposed situation of Plymouth Sound, and the heavy swell that almost constantly rolled in, especially when the wind blew fresh from the south-west to the south-east, made it so inconvenient and so unsafe an anchorage for ships of the line, that, of late years, the fleet employed in blockading Brest, has been in the practice of bearing up, when driven from its station, for the more distant anchorage of Torbay, though little better with regard to security, and worse in every other respect, than Plymouth Sound. It is, for instance, a more ineligible rendezvous for the western squadron, in the chance of the fleet being caught there by an easterly wind, and unable to get out, when it is the most favourable wind for the enemy to put to sea; in the danger to which the ships are liable when so caught at an anchorage, so open and exposed; in the inconvenience, the delay, and the expence of obtaining the necessary supply of stores and provisions from the

other ports, there being none at Torbay;—in short, this open and exposed bay bore so bad a character among naval officers, that Lord Howe used to say, it would one day be the grave of the British fleet.

It is, besides, an object of the first importance to the efficiency of every naval arsenal, to have a safe and commodious roadstead in its neighbourhood, like that of Spithead to the harbour and dock-yard of Portsmouth. Here those ships which may have gone through a course of repair or refitment, or those new from the stocks, may assemble and complete their final equipment for sea; and here, also, ships returning from sea may safely lie at their anchors, till the wind and tide may serve them to go into harbour. But, in Plymouth Sound, ships coming out of Hamoaze, or ships going into that harbour, had no such security: by the rolling sea that set in, they were exposed to the double danger of parting their cables, or striking against the hard and rocky bottom, either of which would be almost certain destruction.

It was most important, therefore, to render Plymouth Sound, if possible, by any means, and almost at any expence, a safe roadstead for ships of war. To ascertain the practicability of this measure, Mr Rennie, the Civil Engineer, and Mr Whidby, the Master Attendant of Woolwich Dock-yard, were sent down by Lord Howick, at the suggestion, we believe, of Lord St Vincent (Earl Grey), in the year 1806, with directions to examine and report, whether by any, and by what means, a sufficient shelter might be given to insure a safe anchorage for a fleet of ships of the line. The report was favourable; and several plans were offered for sheltering this sound, so as to render it capable of containing in safety at their anchors, above 50 sail of the line. Nothing, however, was done or attempted, notwithstanding all the increased and mighty preparations of the enemy, till Mr Yorke presided at the Board of Admiralty; when one of his first measures was to carry into execution this grand and important national object,—the most important that, perhaps, was ever undertaken for the glory and the safety of the British navy. The delay that took place can only be explained by the frequent changes of the Board of Admiralty, which, we believe, have been fatal to many important measures for the benefit and advantage of this great bulwark of the nation. Of the plans proposed for sheltering the sound, one was to throw a pier from Staddon point to the Panther rock, of 2650 yards in length; another, to construct a pier from Andurn point to the Panther, of 2900 yards; and a third, to carry a pier from the same point to the Shovel rock, being only 900 yards.

The objection that was urged against throwing out piers from either of these points, and abutting against the shore, was principally grounded on the certain effect they would have of changing the current of the flux and reflux of the tide to the opposite side of the sound; and of increasing its strength and velocity on that side, while it left all calm on the other; the inevitable consequence of which would be, a deposition of mud or silt in the calm part or eddy, which, in process of time, would shallow the water, already not too deep, to such a degree as to unfit it for the reception of large ships of war.

Besides, of the three passages for large ships into

Plymouth Sound from the sea, the two best are those on the two sides; the worst was that in the middle. Either of the plans, therefore, which proposed piers to be thrown from the mainland, must have destroyed one of the best passages, and left the worst open, which was nearest to the anchorage behind the proposed pier. The middle passage might, in fact, be almost considered as shut up against very large ships by the St Carlos and the Shovel rocks; whereas, if this middle passage should be shut up altogether, it would rather serve to deepen, by giving an increased velocity to the tide, which would scour out the bottom, than to shallow, the two side passages.

On these considerations, Messrs Rennie and Whidby proposed, that an insulated pier or Breakwater should be thrown across the middle of the entrance into the sound, having its eastern extremity about 60 fathoms to the eastward of St Carlos rock, and its western end about 300 fathoms west of the Shovel, the whole length being about 1700 yards, or close upon a mile; stating, with confidence, that such a Breakwater might, with every chance of success in its favour, be constructed; and that it would give shelter to ships in the sound, without any danger of lessening the depth of water.

The middle part of the Breakwater was proposed to be carried in a straight line for the length of 1000 yards; but they recommended that the length of 350 yards at each end should have an inclination towards the straight part, in an angle of about 120°. See the figure, Plate XXXVIII. These inclined ends would not only give shelter to a greater extent of the sound, but would, in a greater degree, prevent the rushing in of the tide from agitating the water at the anchorage, than if the two extremities were left in the same straight line, and at right angles with the direction of the current into the sound.

It was also proposed, in order to cover the sound more effectually, that a pier should be thrown from Andurn point towards the principal Breakwater, of about 800 yards in length, with the same inclined point of 120° as the head of the Breakwater. This pier, however, does not appear to have been thought necessary, and might have been in some respect injurious to the sound. It might, however, have made Bouvisand Bay a good anchorage for frigates and smaller vessels, and given them the advantage of a fine stream of fresh water, which falls into that bay.

It was recommended, as the most practicable and best mode of constructing this great work, to heap together promiscuously large blocks of stone, which were to be sunk in the line of the intended Breakwater, leaving them to find their own base, and take their own position; and it was conceived that stones of the weight of one and a half to two tons each would be sufficiently large to keep their places, without being rolled about by the tremendous swell which, in stormy weather, is thrown into Plymouth Sound, and thus avoid the inconvenience and loss of time and labour which the French experienced at Cherbourg, by throwing down small rubble stones. It was thought, that, in those places where the water was 5 fathoms or 30 feet deep, the base of the Breakwater should not be less than 70 yards broad,

and the summit 10 yards, at the height of 10 feet above the low water of an ordinary spring-tide; that is, the dimensions of the Breakwater, in those places, should be 40 feet high, 30 feet across the top, and 210 feet wide at the foundation.

The surrounding shores of Plymouth Sound and Catwater were next examined, with a view to determine from what quarter materials for this great undertaking could most conveniently be obtained, as to quality, cheapness, and celerity of conveyance. On the west or Cornish side of the sound, nothing appears but hard granite; at the head of the sound and in Catwater, on the Devonshire side, all is marble and limestone. In Catwater alone, it was estimated, on a rough calculation, that 20 millions of tons might be procured in blocks fit for the work, which was about ten times the quantity that would probably be wanted. The time required for the completion of the work, would depend on a variety of circumstances. It is obvious that, if the two sides of the sound had furnished proper materials for the purpose, the time would considerably have been abridged, as, in that case, when the wind was easterly, vessels might deposit stones on the eastern end of the Breakwater, and in westerly winds, on the western extremity, and the work would thus be proceeding with an uninterrupted progress; whereas, if the stone was to be brought from one point, and that point on the shore of Catwater, a strong southerly and south-westerly wind, those most prevalent in this country in the winter months, would generally impede and frequently render it impossible for vessels to go off with their cargoes.

Catwater, however, having many advantages, and especially for the convenience of loading the vessels, and the facility of procuring blocks from the quarries of any size, was considered, on the whole, as entitled to the preference over any other place. Besides the quarries here being in the neighbourhood of villages, lodgings and conveniences would be afforded for the workmen; and, on the whole, it was calculated that the work might be completed from hence at a cheaper rate, and perhaps in less time, than from situations much nearer to it, but much more exposed to the wind and waves.

An estimate of the expence could not be made with any degree of accuracy, as no correct section of the bottom had been taken. Supposing, however, the great Breakwater to be 1700 yards in length, 30 feet in width at the top, when carried 10 feet above low water of spring-tides, with a slope on the southern or sea side, of three horizontal to one perpendicular, and, on the sound or land side of one and a half horizontal to one perpendicular, it was calculated that the whole mass of stone required, would be about two millions of tons. If then 100 sail of vessels of 50 tons burthen each were employed in carrying stone, and that each vessel was to carry only 100 tons a week, the quantity deposited in one week, would amount to 10,000 tons, or say 500,000 tons a year; and, at this rate, the Breakwater would be completed in four years; but making allowance for time lost in preparations, contingent delays and unfavourable weather, and deductions in the quantity of stone for the shallow parts over which the line of

the breakwater was carried, the completion of the work might safely be calculated within the period of six years.

Nor would the building of the pier from Andurn point, if so determined, increase the time of completion. If carried from the shelving rocks within the point, leaving a passage between them, the pier would require about 360,000 tons of stone, which, by employing about 30 vessels, might be deposited in three years.

It was recommended by the gentlemen above mentioned, that the great Breakwater should be begun on the Shovel and extended on both sides of it, as, by so doing, the effect produced on the sound would be observed as the work proceeded; and that buoys should be placed along the line, so that the whole of the vessels employed might, if necessary, deposit their cargoes at the same time without interrupting each other.

The rough estimate for completing this great national work, made on the grounds above stated, was as follows: