DRY DOCKS.

New Zealand Herald, Volume IV, Issue 1120, 17 June 1867, Page 3

DRY DOCKS.

To tho Editor of the New Zb\la.hd Herald. Sin, —The propriety of constructing a dry dock in the harbour of Auckland lias recently hcen observed upon in the public journals with milch eagerness, and a large amount of favour shown to the pioject, from which it might be inferred that but little or any difficulty was in the way of accomplishing such, a very desirable work: before, however, we further entertain the subject of a dry dock, constructed after the manner of those at home, it becomes a matter of the very gravest consideration, first to Know what would be the character of the works which would meet the sanction of the Imperial authorities; how far such works would be suitable for the port -of Aucklnnd ; and if suitable, what; would be the final cost to the province ? There exists at present, I think, ample data (without any further expenses whatever) to determine these points with sufficient accuracy, so as to guide us to the best course to be puisued. In the first place it may be taken for granted that to obtain the approval of the Admiralty, a dry dock must be constructed in masonry— must have not less than 2-1 feet of water on tho fill of the gate at high fater —be 350 feet long, and SO feet wide, so as to admit first class vessels of war. > ow, as the rise of tide on the TCnglish coast is very much more than in this colony, it follows, that the first cost of such works here must largely exceed those at home, by reason of the increased cost of founding them, and of the much higher price of skilled labour here. It follows, also, that when constructed, the working expenses must also be much greater ; for, assuming a dry dock to be constructed after the plans of the Admiralty, with so small a rise of tide as we have here (11 feet), it will be found that a dock having 24 feet of water on its eill at high water of spring tides, would leave 13 feet in depth to be pumped out every time it was used ; and in a dock of the dimensions I have •named, there would be about 1.750,000 gallons of water to be pumped for every vessel docked. Dry docks of masonry are, for these reasons, best suited to lo ahties where the rise of tide is considerable; otherwise placed, the charges upon a vessel using such a dock must of necessity. be very great. We should, therefore, pause before undertaking the construction of a dry dock to suit the views of the Imperial Government. and not be tempted with the prospect of a loan of some £20,000 at £l per cent; lor this amount would, most probably, be found not more than sufficient to erect coffer-dams and place the nee-.ssary plant "upon the ground, and I think it will be found that to construct dry docks to suit the views of the home authorities, merely for the sate of an Imperial loan of £20j00 or so, would be the most fatal policy the province could pursue, simply because we should have to incur an expense beyond this loan of certainly pot less than £130,000 for the sole purpose of providing dock accommodation, of a special character, for Her Majesty's Navy, wlien tlie same thing can be accomplished by other modes of construction. Putting aside any prejudice whieli may exist iu the Navy against repairing a vessel of war anywhere butiudrydoeksas constructedathome, it docs nst follow by any means that because expensive structures of masonry are adopted in lingland, that the same plan should be followed here, for the rise of tide, the value of skilled labour, and the financial condition of the two places, are very dissimilar, and these three conditions should regulate the character and cost of the works to be undertaken. It would, however, be necessary, for the future protection of the'colony, that any marine works proposed as

a substitute for dry docks of masonry sho contemplate tlie reception for repairs ot largest class of men-of-war, and no stru having a less depth of water tlian 24 feet would be found perhaps satisfactory. n „ n -ons If we would seek an example of the j and cost of a modern dry dock of mas /> one it is probable the I m per l a Go™ lont1ont might call upon the Province to may take the eastern dock i are still larger dry docks than believe, as to admit vessels 400 feet lon S- , to found the walls of such structures asthese in the Waitemata, the coffer dams would be enormously costly, and the whole cost ot the works being far beyond the resources of the province, reaching, in my opinion, to of not less than from £100,000 to £160,000. 33ut why should we build dry docks of masonry, as followed at home? J rather to look to the practice of otl ei• coiin tries, circumstanced as to tides ditions as we ourselves are, and lef J ll ti vestigate the plans and modo of construction which have been followed there. _ . In North America, where the ri-.e of tide is small and labour dear, dry docks of masonj are not the rule, but the exception : the Amen cans have avoided the great cost of such That extremely energetic nation has made extraordinary progress in inventions an co ' vances for the repair of vessels llich T.' suited to a new country, perfectly adapted to the very limited rise of tide, and so modeiate So cosVthat we cannot do better t urn follow their example, by directing our attention to tlie atroductionofsome one of their contrivances as a substitute for a dry dock of masonry In works of this nature they have been successful to a high degree, both as to efficacy and linnta-

tl °lt < i3 well'known tliat on the south portion of the American coast, the rise of tide is ver y small. At New York the rise is only about 5 feet, while in the Gulf of Mexico the rise is only IS inches, and henco the construction ot dry docks of masonry, under such conditions, would have been attended with an immense outlay and heavy permanent annual charges, which, as a rule, the Americans hare avoided. Under the most favorable circumstances the construction of effective dry docks is known to engineers as one of the most costly of operations, involving, in some cases, immense untorseen difficulties, and an outlay very far beyond that estimated, and as before observed, it should he borne in mind, that where the rise ot tide is small, the cost of construction becomes largely increased, and the working of such docks is expensive, because a large proportion ot tlie "water contained in tlie dock must be puinpcd out every time a vessel is docked, for "which, expensive machinery must be provided and a permanent stafi of officers paid. Hence diy docks of masonry are looked upon in America as works to be undertaken by the nation alone ; indeed, I believe that at the present day there are not more than three dry docks of masonry in the whole of the United States—one at Boston, another at Norfolk, and a third at JNcw York, all of which are exclusively applied to

the purposes of the American davy. The dock at Boston measures, we are told, 306 feet in length and 86 feet in breadth, having a depth of water of 30 feet—but, although the depth of water is 30 feet at high water of spring tides, the fall of tide is only 13 feet, which leaves 17 feet o f water to be pumped out. The cost of this dock is said to have been £152,000. The dry-dock in the navy yard of JNcw York, is said to be 350 feet long, 98 feet broad, and to have a depth of water of 26 feet. Great difficulties occurred in its construction, and the cost reached the large sum of £400,000. These are examples of the cost that the Province of Auckland might be called upon to find, if a dry dock is to be provided suitable for the use of her Majesty's vessels of war ; and, as a further example, I may draw attention to the estimccted cost ot the proposed dry dock at Port Chalmers, plans of which have been prepared by Mr. Balfour. There, it appears, the depth of water for docking purposes will rarelv exceed 17 feet at high water of spring tides. I need scarcely say that this depth will not satisfy the Imperial authorities, because quite ■unsuited to large vessels of war, and therefore a loan from the Home Government can hardly he sought for. Yet, with special advantages of good building stone being found close to the site of the works, and a favourable bottom said to exist, the estimated cost is £56, What the final cost may be, should any unforseeii difficulties arise, it is not possible to say. These examples all point out to us very plainly, I think, the certainty of a very large expenditure being necessary to provide a dock j ■which would meet the approbation of the Imperial authorities, and should warn us against incurring any expenses whatever, having that object in view, except the way to provide the cash and pay the interest thereon, is perfectly clear. To remedy these drawbacks we must look to America. There, to avoid and overcome the enormous cost of dry docks, as usually constructed, and to meet the growing demands of the mercantile navy of the United States, they have adopted, and most successfully used, several contrivances which are perfect substitutes for dry docks of masonry, by which a vessel can be docked, repaired, and again floated in much less time and at far less cost than when using the ordinary dry docks in harbours where the rise of tide is small. Amongst these contrivances are Thomas's marine railway, the screw dock, the hydrostatic dock, the sectional dock, Clark's floating dock, Barron's floating dock, and dry docks constructed on Caldwell's principle. The facility of repairing vessels of the largest class, afforded by some of these inventions which have been used, are as great as can be desired, while the cost and time of repairs appear to be reduced to the lowest figure. The various contrivances appear to have been used according to their adaptability to the localities; for instance, the screw and hydrostatic docks are used at New York, the marine railway at Philadelphia, and the screw dock at Baltimore. The very limitedcost of many of the American works, used as substitutes for the ordinary dry dock, and the immense facility given to the mercantile navy of that great country, should induce us to copy them: for X have no doubt but that all the advantages afforded by ordinary dry docks, could be secured at a gross cost not exceeding £35,000. To conclude, I may say that my object in addressing to you this somewhat lengthy communication, has been to draw attention to this case, and to suggest caution, as the probability is great, almost amounting to certainty, that dry docks, on the English system, cannot be constructed in the Waitemata, to meet the appreval of the Imperial authorities, except at a cost so great as to exclude them from consideiation by so young a colony, and that, if this be so, there are other modes, already well tried, of obtaining the fullest amount of accommodation for the rapid and safe repairing of the largest class of vessel, at perhaps one-fifth the cost of an ordinary dry dock of masonry. It is to be hoped, however, that if I am correct in my views, as to the probable cost of a diy dock of masonry to suit the Admiralty, that it will not delay or retard the construction of other works in substitution, securing the same safety, and rendering the same facilities, at far less cost, and over which the Imperial Government would not, necessarily, have any control.—l am, &o, Henet_ Wbigg, Civil Engineer, Aucklßtt(3,lotli June, 1867.

OUR DUES. To the Editor >of the New Zealand Hbbald. 1 Sir, —Our representatives "will soon e wing" for the purpose of attending to their live duties " down South." Many important subjects ■will doubtless engage tlieir attention, and •n®' B . likely the recently imposed stamp duties will com for a share of notieo. Now, Mr. Editor, ICS /' very hard times, and as every little helps to mafeeuie muckle these stamps do their full share towar * creasing the already excessively burthened shou of the inhabitants of New Zealand. Now, you think we are likelv to have any mitiga 10 " , thean taxe.-i as the result of the forthcoming ?. es ? , I hope sr>, but Inm afraid not. As the canm | has once tasted blood will not lightly oreg ■ "luxury," so our dictator and his instrumen s ( surely thoy cannot bo regarded as c °' n „ . w . be found quite unprepared to lessen the ilow bees 'nto the trea-ury from this sonrce. course neees?a r y that ornatn ministerial reel e 1 ' costly Panama postal services, expensive pr g establishment, reporters, &c., should be hep up doed the interests of the " Empire ci l 'y , e .

that they should be kept up—and while this is so u is it not the highest presumption on the part, ot tlie taxpayer to offer an opinion P let him rather kiss v the rod and feel thankful it is not a scorpion. o, Mr. Taxpayer, don't you may wish you may get.it. j Well, sir, if our representatives can do anything towards decreasing the lavish expenditure of Government and thus lighten the burdens of the peoplo they will deserve our best thanks, but it this may not be • so, there is at least one thing which should be done: ' lot us have full value for our money, which it cannot ■ be s»id we at present roceive—from the notoriously--1 defective Panama servico down to the penny stamp 5 d ues—and it is tj the latter lam at present referring, l Do you think, sir, that we should " memorialize the r head ot this department with a vitw of having a sufficient coat of adhesive gum laid on the Btamps S which the Government sell, au i thus givethebuyerlus , full '* penn'orth," as well as save a good deal of mconl venience to the unfortunate 1 Gumsuckbb. Juno 15, 1867.