302 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



Sep 



T E M 1! K R , 



other gootl qualities which I shall hereafter show to attend her pro- 

 portions, by the alteration of form in the horizontal direction alone. 

 VVe have next to consider how the relative merits of the two vessels 

 will stand if it he required to give the same speed to both with the 

 same power. Their relative resistances beit)g as 7 to 0, we will sup- 

 pose that the velocity attained by the narrower vessel with a given 

 power is sufficient for the wider; to reduce the latter to the speed of 

 the former, we again have recourse to the priuci|jle of the wedge, by 

 making a b bear the same proportion to c d, or 10 feet as 7 to 9. We 

 thus find as <) : 7 : : 10 : 31-11; then 6 c 20 X 15 fthe depth) 

 X 3M1 = 9333 cubic feet, the amount by which the bulk of the wider 

 vessel is decreased to attain the same speed as the narrow one. But 

 the latter was shown to lose only '.HJOO cubic feet of her bulk by this 

 means, and she has still therefore an advantage of 333 feet over the 

 wide vessel, 333 will divide about 360 times into 120,000, therefore 

 the wide vessel sacrifices l-3(;oth part of her bulk more than the nar- 

 row one to attain the same speed by alteration of her horizontal form ; 

 but this amotuit is so small as to be quite inconsiderable, for in a vessel 

 of 2000 tons burthen the difference will be but 3^ tons. 



Tims much as to the diminution of resistance by alteration of the 

 horizontal form ; let us now inquire how the same effect may be pro- 

 duced by altering the vessels in their vertical section. Let fig. 1* re- 

 present the vessel of 40 feet beam, and fig. 2* that of 30, in elevation, 

 or longitudinal section. The depth a h equals 15 feet in fig. 1*, and 

 20 feet in tig. 2*. To reduce their respective resistances as before to 

 one half, we make h c equal to twice a b, viz., 30 feet in fig. 1*, and 

 40 feet in fig. 2*. They are then reduced in bulk as follows: fig. 1* 

 by 15 X 15 X 40= 9000 cubic feet, and fig. 2* by 20 X 20 X 30 = 

 12,000 cubic feet, showing a difierence of 3000 cubic feet in favour of 

 fig. 1*, being exactly what was lost when reduced in her horizontal 

 form to give the same results. Again, to reduce the speed of fig. 1* 

 to that of fig. 2*, make 6 c : 30 : : 7 : 9, thus bc= 23-33 feet, and 

 23-33 

 — ^ — X 15 X 40= 0999 cubic feet, making a difference in bulk of 5001 



cubic feet in favour of fig. 1*, at the same velocity as fig. 2*. Com- 



x'ig. 1* 



J*- 



Water 

 Line. 



Fig. 2" 



a_ Water 



' Line. 



paring these results we see that giving the wider vessel the same 

 speed as the narrow one, she lost 333 cubic feet more of her bulk than 

 the latter, by doing the same by change of form vertically she has an 

 advantage of 5001 cubic feet.* As it is almost always necessary to 

 employ both these methods of reducing a vessel's resistance, I shall 

 suppose them equally applied, and deducting the loss from the gain 

 ■we have still 4GGS cubic feet of bulk remaining for buoyancy or stow- 

 age in favour of the wider vessel when the two have the same velo- 

 city ; and as the loss in preserving her advantage of 7 to 9, by change 

 of horizontal form exactly equalled her gain in cloing so by the vertical 

 alteration, if both means are equally employed we find she preserves 

 her advantage in speed without any loss of bulk whatever beyond the 

 narrow vessel, and, as I think can be proved, with many points of 

 superiority in other respects. I have considered these effects as ap- 

 plied to bodies of simple parallelogramic forms in the first instance 

 for the sake of simplicity of illustration, but the principle is applicable 

 to all forms ; and as regards vessels with sharp bottoms, and of a 

 breadth of beam say equal to the wider vessel supposed above, and of 

 a draught equal to the narrow one, their resistance may be resolved 

 into that of parallelograms depending in their proportions of depth 

 and width en the acuteness or obtuseness of the angle which their 

 bottoms make at the keel, and on the depth of their bilge or union of 



■» The j^merican river steamers referred to in the eenversalion at the Civil 

 Ergineer's Institution on Mr. .Sea«ar(l's table of velocities, are described as 

 (liminisbed )iriiicipally in the vertical direction; ihev have been apth de- 

 scribeil as having ■' spoon entrances." 



the sides and bottom below the water line. I shall have occasion 

 again to refer to this part of my subject when I come to speak of the 

 comparative stability of vessels of different transverse sections. At 

 present I shall only remark that the results of the above calculations 

 are fully borne out by all the seagoing steamers I am acquainted with. 

 For instance, the Gorgon and Cyclops of 1200 tons burthen and 320 

 horse power, having good beam, have performed excellently ; while 

 the Liverpool, in her first state of 1042 tons burthen, and 460 horse 

 power, through great deficiency of beam, was a miserable failure; but 

 since her alteration, though greatly increased in tonnage bv the addi- 

 tion of 7 feet beam, she gives more satisfactory results with the same 

 power than any of the large steamers built for crossing the Atlantic. 

 The Great Western registering 1340 tons, and of 450 horse power, 

 having pretty fair beam, was the only one of the New York steamers 

 which could be said to answer, until the Liverpool was altered, since 

 which time the latter seems to have the advantage. The British 

 Queen and President have completely nullified the calcidations of 

 their projectors, and Mr. Cunard's steamers, almost equally deficient 

 in this respect, employ about 500 horse power to do what, judging 

 from past experience, the Gorgon* and Cyclops would in all probability 

 easily effect with 320. I think these results, independently of others 

 which, with your permission, I shall hereafter adduce, are suflScientto 

 prove the fallacy of the almost universal belief among shipbuilders 

 and others that narrow vessels are necessarily faster than those of 

 greater beam. So strongly however is this opinion held, that I knov7 

 that shipbuilders of considerable experience and ability have declared 

 that no steamer should have beam in a larger proportion to her length 

 than as 2 to 13 ; or in other words should have no less than G J breadths 

 to her length; a proportion which has proved insulBcient in most of 

 the ])oints which I named as necessary for a seagoing steamer : and 

 for the sake of this dogma though sometimes giving their vessels very 

 good horizontal lines, they sacrifice all the advantages they might 

 obtain by a proper application of the reduction of body vertically, and 

 are obliged from their want of beam, to trust to the enlargement of 

 their bows above water to prevent their constantly shipping water 

 forward, involving defects which I shall endeavour to make clear if I 

 continue the subject. The subject of long narrow steamers of small 

 draught in proportion to their beam, which have had many advocates, 

 will occupy another part of our consideration, and I refer to it here 

 merely to say that it is not overlooked. I believe the late system of 

 computing tonnage for shipping has had a great share in producing 

 the defect in point of beam which is to be observed both in our sailing 

 merchant vessels and in our mercantile steamers; for inconsequence 

 of the gross absurdity of assutning a fixed proportion of depth for 

 every vessel, namely, half of their measured breadth, and 94 as the 

 divisor for reducing the cubic result of the three dimensions to tons, 

 however different in form the vessels might really be. Merchants and 

 shipbuilders universally endeavoured to gain as much as possible on 

 their registered tonnage, by giving depth beyond the imaginary 

 standard, and a form fore and aft which should give an absolute amount 

 of bulk much above the -nr^hs of the parallelogramic solid which were 

 supposed, by the use of 94 as a divisor, to remain after reducing the 

 vessel by the sharpening of her bottom, entrance, and run. This style 

 of building has been frequently carried, as too many fatal instances 

 have proved, far beyond the limits of safety, while vessels of really 

 good proportions and fine form being registered by this method of a 

 much greater tonnage than their real burthen, had an absolute fine in 

 the shape of duty imposed on their good qualities. — In the fruit trade 

 and others especially requiring speed, this has led to the building of 

 deep narrow vessels sharp forward, and lean and hollow abaft, gaining 

 somewhat in tonnage, but wanting in all really good qualities, being 

 the wettest and most uneasy vessels which leave our ports. The 

 numerous beautiful models which have fallen into the hands of our 

 merchants as slave prizes have for the same reason, almost without 

 exception, been lengthened and raised upon, have had all their fine 

 points destroyed, been greatly reduced in speed, and frequently be- 

 come exceedingly unsafe vessels, as was the case with a most beautiful 

 slave schooner sold for the turtle trade in this port a few years ago, 

 which having been raised upon, lengthened, and square rigged, went 

 to the bottom on her second voyage. Since the passing of the New 

 Tonnage Act, which assigns as nearly as possible the real contents of a 

 vessel for her register, it might have been expected that some 

 improvement would have taken place in the models leaving the stocks 

 in our merchant builders' yards, but so strong is habit, especially bad 

 habit, and so rooted is prejudice, particularly in matters where ex- 

 pediency and not principle has been the ruling power, that hardly any 

 use has been made of the advantages offered by the new act, and our 



T SeeC. E, and A. Journal, vol. 1, p. 385. 



