CENTRIFUGAL PUMP DREDGING IN'N.S.W. CXXVII. 
of the great expense and length of time required. With regard 
to the number of spuds—in the Von Schmidt type—he certainly 
thought there would be more risk with one than with two, for it 
must necessitate the constant shifting of the whole plant, the first 
cost would no doubt be less, but the work would be done more 
satisfactorily with the two spuds. 
Mr. Portus replying to Mr. Haycroft’s suggestion, that rubber 
should be used for the joints as was done in America, stated that 
rubber had been tried here but had not stood the pressure as well 
as leather, the latter material too was cheap in the colony and was 
sent from Holland with the first outfit of pipes. It was intended 
however, to use rubber with imbedded spiral wire for suction 
joints shortly. The single spud system of working would not be 
applicable for the “Groper” type of dredge, but could be used if 
the suction pipe projected sufficiently past the opposite end of the 
dredge to enable the vessel to cut its way by are dredging as 
carricd out in the United States suction dredge “Ram.” The 
Mississippi type of dredge “Beta,” had many advantages and 
would probably be the ideal machine of the future. 
In reply to Mr. Allan’s question as to whether interest and 
depreciation were included in the cost given of dredging by sand 
pumps, he stated that interest on the cost of plant was not 
included, nor was depreciation in value ; but all expenditure 
for repairs and for upholding the machinery in a high state of 
efficiency formed part of the quoted cost. The reason of interest 
and depreciation being excluded was that in nearly all quotations 
by Governments or Harbour Trusts, these two items were 
excluded, and for purposes of comparison this custom had been 
followed by the Harbours and Rivers Department of this Colony. 
Mr. Wheeler, Mm. Inst. ¢.E., in his work on Tidal Rivers published 
in 1893, writes :—‘ Where a sufficiently large amount of material 
has to be removed to warrant the purchase of plant and the 
employment of a regular staff, dredging in sand can be done with 
Screw hopper suction dredges, including transport, wages, coals, 
repairs, and all expenses except interest and repayment for plant 
