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January, 1913 would take even less power at sea than the smaller on account of size. The first vessel is an oil tanker and the second a United States naval collier of the Mars class. Example No. 2 An interesting case of extravagant design came up recently. A shipping firm had plans of an 11-knot steamer built in Europe' of the following general dimensions:--400' 0" x 52' 0" x 34 0%. They wanted a duplicate built here, but with machinery for 10 knots only. The suggestion that the steel hull could be built 6 per cent THE MARINE REVIEW at piers. "There was no question ot repeating an order. Example No. 3 In heavy bulk carriers it is desira- ble to know how full a vessel can be made, keeping capacity down and so having no more ship than is neces- sary. A; omajority of ship designs on this coast are prepared for light cargoes occupying large space, where ship dimensions run large per ton deadweight; hence the saving in ship dimensions possible when carrying ore, for instance, is apt to be over- looked. COMPARISON OF PROPERTIES, <a ea , a fee Ane" oe 7 if ae | 1 | ELG.. Lk. ee Je '" " | eal | 4 / bod ues | ay eS a : é Z\-G cheaper to modified dimensions with- These' vessels are frequently run out affecting the coal bill was rather a shock to the prospective owners. The . vessel as. redesigned, with identical deadweight, draught and cargo capacity, worked out at 370' 0" ~m RA Oe ok a Oe he. power worked out as follows: 400-ft. 370-ft. Item. ship ship. Skin Hr. Pao ee 685 645 Resiauary Ee Th. Po. us ee: 365 405 otal oo a as 6 eee ces 1,056: 1,050 These are for 10 knots in each case. In addition to less first cost, the shorter boat will be handier at sea, more easily taken care of as re- gards stability, and occupy less space at only 9 knots, even though they have some margin of power; problem resolves itself into one ot finding the range of dimensions where the total resistance remains constant, even though the component parts vary. In a design to carry 7,000 tons deadweight it was found practicable to increase block coefficient from 0.75 to 0.78 and reduce length from 360 to 340 ft. for the same effective horsepower at 9 knots; this repre- sented a 5 per cent saving in steel hull, Beam and draught remained con- stant. i This the preceding problem and the. 19 one are merely examples of search- ing for the economical limit of speed, on which subject a good deal has been published from time to time. While the temptation to keep pow- er down by fining the Ship is a strong one, especially when owners expect a very low coal per diem rate, ship designers should never allow the dimensions to run up _ be- yond what this somewhat elusive economical limit requires. Example No. 4 Quadruple expansion machinery versus triple for long voyages. The author recently had a_ very forcible example of the saving possi- ble if quadruple expansion machin- ery were fitted in a cargo steamer designed to carry 7,000 tons of pay- ing freight for a distance of 14,000 miles, oil burning. The figures came out as follows: 'Quadruple. Triple. i Ce Item. Ft F Length Sogn eee 400 410 Breadth 3.45 ees so ees ee 53 53 Dravight or oo aan ee 27 27 Tons. Tons. Ship, 6 pena oe ee 4,125 4,160 Gateo. eee SA anna aoe uaes 7,900 7,000 Oil, crewyands water. iis. ws 1,900 2,200 Displacement 4.6 365.505 eg 13,025 2 13,560 Speed) Rnots: 4.0.6 eae ewe 11 Vy oe Peo ne 2,750 2,800 Savings: per 'voyage... i. ens. $2,500 Be Extra fist) cost... sa ee $10,000 Pee It will be seen that the extra first cost is récovered in four voyages, and after that a steady gain per voy- age is apparent. This is not strictly an example of economy due to ship form, but has been inserted as being perhaps of interest. a Example No. 5 From the point of view of economy due to machinery, it can be shown that single-screw propulsion is cheap- er than twin screw, the advantage of twin screw being in greater immuni- ty from breakdown, a point by no means negligible in passenger and perishable cargo ships. This is well known to the members of the society and is only mentioned to make the examples more complete. Example No. 6 Recently published photographs of our latest battleships in dry dock reveal a peculiar bulbous form of bow, the load water-line being nar- rowed and the displacement made up by filling out the lower water-lines. Experiments at the model tank in Washington show a material saving due to this form, the bow waves being naturally lessened by the fine upper water-lines. The superintendent of one of our coastwise lines of steamers has had the courage to adopt this form of bow for a 12-knot cargo steamer, in which a 3 per cent saving would