TIMARU HARBOR WORKS.

Temuka Leader, Issue 2189, 16 April 1891, Page 4

TIMARU HARBOR WORKS.

(Continued ) “ Beport of Commissioners dated 2nd April, 1891, in compliance with Chairman’s letter dated 2lst March, lf|9l. ** N.B. - This i is - signed by Mr O’Connor only, Mr Goodall sending in separate memorandum.* Timaru, 2hd April, 1891. Re Timaru Harbor Works. .... “ Appendix to Beport by Messrs O’Connor and Goodall. “ List of some of the suggestions for dredging which have been considered, and the reasona'why they have been rejected. Suggestion No. 1. “ Priestman grab dredgers, (as many as may be found necessary (to work on breakwater, and discharge into elevated bin or bina also on breakwater. The stuff taken from thence by ■teaof , Uop > pbr l barge. “ This would probably be a cheap but it had to be rejected for the rfealon that it would only work satisfactorily, for any considerable length time,sin the event^ of?. the shingre acciinfMatidn reaching the breakwater in a uniformly progressive manner. This it would not be at all safe to reckon-upon. It certainly has not been so in .the past, There is however, more apparent probability, pf it being so in the future, and it is to iome>extent on the assumption that it will be so for at any rate considerable periods at a stretch, that we have recommended the employment of the board’s existing Priestman grab digger* pending the procuring of the pump hopper-dredger. Suggestion No 2. “ Priestman grab dredgers as before but working on a peroid staging outside the breakwater, following up the outer margin of shingle accumulation to such extent as might be necessary and discharging into trucks on staging alongside*—The-truoks to be run on staging and tipped into elevated bin or bins, <on outer or inner side of breakwater and wharf, and the stuff to be taken thence, by steam-hopper-barge. The reason , for rejecting this suggestion the cost and inconvenience of trucking the stuff. Suggestion No 3. “ Priestman grab dredgers, working on piled) staging as before, but discharging into elevated bin, on harbour side of breakwater and wharf, by means of a band conveyor.or pipe and water-jet. “ This idea was given up, as we were unable to bit upon any means of making ; it work satisfactorily for moderate cost. , Suggestion No. 4 “ Priestman grab dredgers, working on piled staging as before, but diecharging into side-tip trucks on locomotive line adjoining. “ The stuff* to be thence carried by Government or separate railway to Bashing Bocks. “This plan has no doubt a great deal in its favor, but the frequent crossing of railway to shipping wharf would probably be an inconvenience, and the cost per ton dredged would be somewhat higher than the plan which we have recommended. “ Besides this too (and this applies to aUihp alternatives except the one whidK? we have recommended) the appliances for this system could only be utilised to their lull extent in one particular way, whereas the great bulk of the expenditure for the system we have recommended would be on a vessel which could be utilised in several different ways, both inside and outside the harbor. Suggestion No, 6.

"A pump dredger, capable of lifting 400 tons of sand or gravel in an hour, forking on, piled staging outside the breakwater, and discharging into an elevated bin at harbor side of breakwater and wharf. The stuff to be thence taken to Dashing Bocks by Jtoam.hopper barge. “This,is,.we think, the best of all the alternatives except the one which we have recommended. It admit of a much smaller vessel (say one of 'l5O tons, instead: of 300 ton* hopper capacity) being employed, a* it could -get filled from a bin in a Tory lew minutes, and could therefore

keep on conveying stuff almost continuously, instead of intermittently, with* dredging " operations intervening. sorhe objection in risking 1 si> ■’ 'expensive a ' machine on staging outside the breakwater, and the plant as a whole (as already mentioned) could not be used to the Miopia extent jn various ways, as the plant which is recommended. Also, although the firsts cost of machinery f>nd consequent interest and depreciation wduld be less than' for the system we have recommended, we doubt .it the ultimate cost of work done would be any less, as there would be two machines Ib ihanV and keep going, in

piece of one. SUGOBTTION No. 6, ;•«! pump dredger, working on piled paging as before, but discharging direct on the beach, in the vicinity of they" Dashing Bocks, by means of a delivery pipe, having a length of about 2 miles. This, if it would act satisfactorily, would probably do the work required cheaper than any of the other methods which , we have investigated. There is ho certainty, however, that it Would do the work required satisfactorily. Delivery pipes of considerable length, we believe in some cases up to 2 miles in length, have, we believe, been successfully used in

connection with pump dredges, bat the material dredged, in all such case, that we know of, has been fine sands Whether or not equally satisfactory results could be obtained with the character of stuff required to be dredged at Timaru, and how the cost of such dredging and delivery would compare with the ascertained cost of dredging «nd delivering fine sand, it is not possible to say with the data at present at our disposal, and the uncertainty about the matter generally i is therefore so great that we are not justified in recommending this process for adoption, in spite of its possible cheapness. As against this possible cheapness, too, there is the consideration, already alluded to, that the machinery thus provided could ' only work in one way, whereas the machine which we recommend to be procured, could work in many ways. Suggestion No 7.

A pump dredger working on piled staging as before, blit discharging into side-tip trucks on locomotive railway trucks alongside. This idea has really nothing to recommend it, as the only object of railway line is to obviate difficulty pf conveying stuff from staging to hopper barge (or to-elevated bib, on its way to hopper barge) and if a pump dredger is employed on the staging of course no such difficulty would arise.

The cost of carriage by barge is cheaper than by railway, including of course, in both cases, the cost of maintenance, repairs, and interest and depreciation, &c, f so that it is only in the case where the cost of getting stuff from dredger to bin would- be considerable, that the carriage by railway alternative seems to show any advantage at all. This statement, however, is subject to qualification to this extent, that whereas it is not an absolute certainty that stuff can be placed' by means of a steam barge, in such a position in the vicinity of Dashing Bocks that it will be thrown up* on- the-beach-ready to be carried on by the wayes, there is no doubt at all that stuff could be so deposited by means of aide-tip trucks, working on a locomotive railway in conjunction with a staging and shoots at Dashing Bocks. There is, however, so very little doubt as to steam hopper.’acting satisfactorily in this particular, that we think such doubt may safely be disregarded. Suggestion No 8.

“ A ladder dredger, working on piled staging, ontside the breakwater. This would involve nearly all the difficulties of getting rid of the stuff, which appertain to the Priestman process with the additional disadvantage that it would be much more exposed to risk from the sea, and being, comparatively, a very costly implement, that would be a serious disadvantage, if kept on very high and strong,staging, to avoid this, some of the cost of such material would be increased, and the height of lift moreover. would be abnormal.

“ The difficulty of travelling round sharp curves, in order* to follow the shiuge face with a mechine of such length as a laden dredge must necessarily be, would also be very great. It is not, therefore, at all probable that this form of dredge ivould be found satisfactory.

Suggestion No 9

“ Dredging face of shingle bank, in the open sea from a vessel afloat. To do this at i imam, * with a ladder dredge, would of course be impracticable, even in the calmest weather usually experienced here, but ijgftinight at times be done by a Pnestman or pump dredge, Ihe interruptions however would be so frequent that it could not be relied upon to any considerable extent, and so cannot be recommended for general adoption ; but, if the form of dredger which is recommended is procured it might sometimes be found advantageous to use it to face a shingle bank, when the conditions are exceptionally favourable. “As regard dredging proposals generally many other proposal were suggested, and fully considered, but those above described seemed to be the only ones worth specially mentioning. “ 0. T. O’Connob, M. Inst, O.B.” (To be Continued.)