Estimate of the Probable Expense of a Cut-Stone Pier and Two Light-houses to be built on the top of the Great Breakwater.
| 42,000 cubic yards of masonry, in the out and inside walls of the pier, at 27s. | L.44,700 | 0 | 0 |
| 62,000 cubic yards of rubble filling between the out and inside walls, at 6s. | 18,600 | 0 | 0 |
| Paving the top of the pier with large blocks of stone, 8500 square yards, | 22,950 | 0 | 0 |
| Two light-houses, with reflectors, and argand lamps, | 5,000 | 0 | 0 |
| Contingencies 20 per cent. | 28,650 | 0 | 0 |
| L.119,900 | 0 | 0 | |
| Breakwater, | 1,051,200 | 0 | 0 |
Total Estimate of completing the works, - - - - - L.1,171,100 0 0
It was not before the opinions of the best Engineers, men of science, and naval officers eminent in their profession, had been collected, compared,
and seriously considered, that Mr Yorke determined to carry into execution this great undertaking. The principal objection started against it was that it might cause the anchorage in the Sound to be destroyed in the course of time by the deposition of mud and silt along the whole eddy within it. There does not, however, appear to be any solid ground for this objection. The water brought by the tides from the sea is at all times perfectly clear and transparent, and that which proceeds from Hamoaze and supplied by the Tamar and the Tavy, is almost wholly free from any alluvial matter, these rivers holding their course through a fine granite soil. The fact is sufficiently proved by the circumstance of no deposition taking place in the recesses of Hamoaze along the dock-yard wall, which lead into the docks, nor in the numerous eddies that are caused by the projecting jetties and salient angles of that wall. Another objection started against the undertaking was, that, by the diminished quantity of water thrown in by the tide into Hamoaze and Catwater, the Sound would gradually fill up and these harbours be destroyed. No perceptible alteration, however, has as yet taken place in the height of the water in Hamoaze, or in the strength or set of the tides.
A rock of limestone, or rather gray marble, situated at Oreston, on the eastern shore of Catwater, consisting of a surface of 25 acres, was purchased from the Duke of Bedford for the sum of L.10,000; quays for shipping the stone were erected in front of it; iron railways leading from the quarries to the quays were laid down; ships were hired by contract to carry off the stone, and others built at the dock-yard. Mr Whidby was appointed to superintend the work. The quarries were opened on the 7th August 1812; the first stone deposited on the 12th of the same month; and, on the 31st March 1813, the breakwater made its first appearance above the surface of the Sound at low water of the spring-tide. The system of quarrying the stone is conducted with admirable skill, and stones of the proper size obtained with less waste of small rubble than might be expected. In working these quarries an extraordinary phenomenon was discovered in the very body of the great mass of this old marble rock. At the depth of 65 feet from the summit of the rock, and 25 from the margin of the sea, a cavity, or rather a nodule of clay was discovered, of 25 feet long and 12 square, or thereabouts, in the midst of which were found several bones of the rhinoceros, in a more perfect state, and containing less animal matter in them, than any fossil bones that have yet been dug out of rock or earth.
The vessels employed for carrying off the large blocks of stone, are of a peculiar construction, adapted to convey, with ease, masses of marble weighing from three to five tons each. These great blocks of marble are placed on trucks at the quarries, and run down from thence, on iron railways, to the quays, against which the vessels lie with their sterns. The two stern ports are made sufficiently large to receive the trucks with the stones upon them. Each truck is passed separately through the port-hole, on an inclined plane, and run to the fore-part of the vessel, in the hold, on an iron railway.
The two sides of the hold of the vessel are calculated each to contain eight of these loaded trucks, which, at five tons on each truck, gives 80 tons of stone for one cargo. The stones thus placed on the trucks remain till the vessel arrives at the point in the line of the Breakwater where they are to be deposited. By means of a crane on the deck of the vessel, the two trucks nearest to the two stern ports are then drawn up the inclined plane, and run upon a frame on moveable hinges, called the typing-frame; by the falling of this frame, in the manner of a trap-door, the stone or stones are discharged from the trucks on the slope of the Breakwater; but the typing-frame remains, by means of a catch, in the position in which it is left at the moment of discharging the stones, until the empty truck is pulled up by the crane to the after-part of the deck, from whence it is run forward to make room for the second pair of loaded trucks in the hold. The catch being now disengaged, the typing-frame returns to its former position, ready to receive the next pair of loaded trucks, and so on till the whole sixteen have been discharged, and the light trucks run upon the deck of the vessel, ready to be run out at the quay, and from thence to the quarries, to take in fresh loads of stone. In this manner a cargo of 80 tons may be discharged in the space of 40 or 50 minutes. The vessels are placed in the proper places for depositing the stones by means of buoys, and the exact line of the Breakwater is preserved, by observing lights or staves placed at a distance on the shore.
The following description, referring to Plate XXXIX., will convey an accurate idea of these excellent vessels for the purpose they were constructed.
Fig. 1. Shows the stern of the vessel, in the act of depositing the stones. The runner R being hooked to the fore-part of the truck, raises it up, and by that means tips the stone overboard. When the stone is in the act of being drawn up out of the hold, on the inclined plane B (fig. 3.), the runner is hooked to the fore-part of the truck, and lashed down to the after-end, over the stone, which prevents the latter from sliding off the truck, in its progress up the inclined plane. The empty trucks are, for the most part, lodged on the fore-part of the deck, and some placed on an edge against the side of the vessel.
Fig. 2. Shows the stern of the vessel when loaded, with the ports up, or closed.
Fig. 3. A longitudinal or sheer-section of the vessel, when loaded, with the trucks on one side of the hold and deck, showing the number which the vessel usually stows on each side. The stones being frequently longer than the trucks, the number carried in the hold must be proportioned accordingly. In bad weather it is unsafe to send many trucks on deck; and, in general, not more than four are sent into the Sound, in that way, at one time; the amount of the cargoes, therefore, vary according to circumstances, from 40 to 65 tons; the largest stone hitherto deposited being about eight tons.
The after-part of the deck, under the tiller, is divided into two parts, length ways, and made to move up and down; the fore-parts are secured to a beam
by hinges. This moveable deck, when raised, as at X, allows the stones to come out of the hold; and, when down, as at Y, serves to convey the empty truck from the port to the deck, in order to make room for another stone.
D Is a common windlass for heaving the trucks out of the hold up the inclined plane B.
C The hinges of the typing-frame.
Ten vessels of this construction, for carrying large masses of stone, built in the King's Yards, and forty-three hired by contract, averaging about fifty tons each, are employed in conveying stones from the quarries. The contractors' vessels are not of the same construction as those in the immediate employ of government; they carry stones of less weight, which are hoisted out of the hold by a chain and windlass, and thrown overboard. A load of fifty tons is discharged from one of these vessels in about three hours. By all these vessels, the quantity of stone deposited in 1812 was 16,045 tons; in 1813 71,198 tons; in 1814, 239,480 tons; in 1815 264,207; and in 1816 up to 12th August, 206,033 tons; at which time, the total quantity of stone sunk, amounted to 896,963 tons; and at the conclusion of the year to upwards of 1,000,000 tons.
Of this quantity, the proportions of the different sizes of the blocks deposited are nearly as follows:
| Tons. | |
|---|---|
| Of one ton each stone and under | 423,904 |
| — one to three tons each | 309,706 |
| — three to five tons each | 150,593 |
| — five tons and upwards | 12,760 |
The original contract price for quarrying the stone was 2s. 9d. per ton, and the original contract price for conveying it to the Breakwater 2s. 10d. per ton, since which the former has been reduced to 2s. 5d., and the latter to 1s. 10d. per ton. The cost of each ton of stone sunk in the Breakwater, including the building of quays, purchase of land, salaries, and every other expence, according to the nearest calculation that can be made, amounts to about 8s. 1½d., which, upon the whole quantity deposited, gives the total sum expended up to 12th August 1816, equal to L. 364,000. And as the work may be considered as more than half completed, it will be finished considerably within the original estimate, and, if parliament had thought fit to grant the money, within the time.
The greatest quantity of stone sunk in any one week was 15,379 tons; and the part of the Breakwater, at the above mentioned date, above the level of low water spring-tides, was in length 1100 yards. The length completely finished to the height of three feet above the level of the highest spring-tides, and thirty feet wide at top, was at the same time 360 feet. The large stones of the upper part of the Breakwater are deposited to any nicety by means of a vessel constructed for the purpose, having the same sheer or slope at the bow with the side of the work, so that by a projecting beam or mast, the largest stones can be taken out of the vessel, and placed on
the opposite side, or middle, or any other part of the Breakwater.
The small establishment, and the quick manner with which this great work has been carried on, form a curious contrast with the multitudes employed on the Breakwater of Cherbourg, the time occupied by that undertaking, and the parade and ostentation with which it was conducted.
The whole establishment for carrying on the Plymouth Breakwater is as follows:
| Persons. | |
|---|---|
| A superintendent, with proper officers and clerks, to keep and control the accounts | 10 |
| Warrant officers and masters of the ten stone vessels in the immediate employ of the public | 21 |
| Seamen and boys to navigate these vessels | 90 |
| Seamen employed in the superintendents' vessels, the light vessel, boats' crews, &c. | 45 |
| Masons, blacksmiths, carpenters, sailmakers, and labourers, employed at Oreston | 39 |
| In the immediate pay of Government | 205 |
| Seamen employed in the contractors' vessels | 170 |
| Quarrymen, labourers, &c. employed at Oreston by the contractors | 300 |
| Total establishment | 675 |
The result of this great work has completely answered the expectation of its warmest advocates. The good effects of it were, indeed, very sensibly felt at the end of the second year, when about 800 yards of the central part, where the water was shallowest, were visible at low water spring-tides. The swell was then so much broken down and destroyed at the head of the Sound, that the fishermen were no longer able, as heretofore, to judge of the weather outside the Sound; and ships of all sizes, and, among others, a large French three-decker, ran in with confidence, and anchored behind the Breakwater. Since that, near 200 sail of vessels of all descriptions, driven in by tempestuous weather, have, at one time, found safe shelter within this insulated mole, where a fleet of 25 to 30 sail of the line may, at all times, find a secure and convenient anchorage, with the additional advantage of having a stream of excellent water from a reservoir constructed above Bouvisand Bay, capable of containing from ten to twelve thousand tons, or a quantity sufficient to water 50 sail of the line. This water is brought down in iron pipes to Staddon Point, opposite to the anchorage, where it is intended to build a jetty from which the water will descend through the pipes into the ships' boats. The whole expence of this most useful appendage to the Breakwater is calculated at about £16,000.
During the winter of 1816-7, the gales of wind were more frequent and tremendous than had been known for many years; and, on the night of the 19th January, such a hurricane came on as had not been remembered by the oldest inhabitant. The tide rose
six feet higher than the usual height of spring-tides. The Jasper sloop of war, and the Telegraph schooner, being anchored without the cover of the Breakwater, were driven to the head of the Sound, and both lost; but a collier deeply laden, and under its cover, rode out the gale. No damage was sustained by any of the shipping in Catwater; but it was the general opinion, from former experience, that, if no Breakwater had existed, the whole of the ships therein must have been wrecked, and the storehouses and magazines on the victualling premises, and most of the buildings on the margin of the sea, been entirely swept away. Till this tremendous gale, the Breakwater had not sustained the slightest damage from the heavy seas that, through the winter, had broken against it with unusual violence, not a single stone having moved from the place in which it was originally deposited; but after the hurricane above-mentioned, and the high tide which accompanied it, it was found that the upper stratum of the finished part, extending about 200 yards, and 30 yards in width, had been displaced, and the whole of the huge stones, from two to five tons in weight each, carried over and deposited on the northern slope of the Breakwater. In no other part could it be discovered that a single stone had been displaced.
The want of a harbour, or any place of safety to which ships can resort in bad weather, or in distress, between the ports of Plymouth and Portsmouth, led to the suggestion of Portland Roads being converted into a secure harbour by means of a Breakwater. It was estimated that the construction of such a stone dike, extending from the north-east part of Portland Island, about two miles and a quarter in length, covering an anchorage of about four square miles, and completely sheltering the pier, harbour, and bathing place of Weymouth, would require about four million tons of stone, five years to complete it, and an expence of about six hundred thousand pounds Sterling. The capstone alone, which covers the Portland stone, and which, not being marketable, is not only useless, but a great incumbrance, would be sufficient to complete this great undertaking; and the elevation of the quarries, being 300 feet above the level of the sea, would admit of the stone being sent down on rail-ways to the water side, without the aid of either engines or horses; and, on this account, would be deposited at less than one fourth part of the expence which is incurred at the Plymouth Breakwater. Such a secure anchorage in this situation, in which the largest fleets, either naval or mercantile, would ride at anchor in all winds, and the most stormy weather, in perfect security, is not unworthy the consideration of the public; and, perhaps, in the present increased state of our population, and the difficulty of finding employment for the labouring poor, there can be no truer policy than that of carrying on great national works of public utility, were it only for the sake of encouraging industry, instead of expending an equal, or probably a far greater sum, for the support of idleness and the encouragement of vice, in those parochial buildings, too frequently misnamed work-houses. (K.)
Scale of 2000 Toises.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100
A PLAN of
CHERBOURG
with the
BREAKWATER
and the
NEW DOCK YARD.
with Large Blocks of Stone.
- 1. High Water line of Spring tides.
- 2. High Water line of Neap tides.
- 3. Low Water line of Neap tides.
- 4. Low Water line of Spring tides.
BREAKWATER.
PLATE XXXVIII.
SKETCH OF PLYMOUTH SOUND.
TRANSVERSE SECTION of the FINISHED PART of the BREAKWATER.
High Water Spring Tides.
| 12 | 13 | 14 | 15 |
| Low | 16 | 17 | 18 |
| 19 | 20 | Spring | 21 |
Eng'd by W. Archibald, Esqr.
BREAK WATER.
PLATE XXXIX.
FIG. 1
FIG. 2
Scale
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920 921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958 959 960 961 962 963 964 965 966 967 968 969 970 971 972 973 974 975 976 977 978 979 980 981 982 983 984 985 986 987 988 989 990 991 992 993 994 995 996 997 998 999 1000
FIG. 3