434 



FOREST AND STREAM. 



[Nov. 16, 1895. 



really beaten by superior power and not by the mere use of the cen 

 terboard. 



In conclusion, while the centerboard has been at times an instrument 

 of evil through the easy way which it opens to bad design and con- 

 struction, the device, when properly handled by the honest and skill- 

 ful designer, is of the highest possible utility. Through it is made 

 possible a craft of extreme light draft which, though capsizaMe, is 

 still reasonably safe and exceedingly useful in skilled hands; and no 

 other should attempt to use it, With adequate depth and a proper 

 construction, the material being preferably all metal in large craft, it 

 gives a strong, safe and practically noncapsizable sea-going ves- 

 sel, for either pleasure or trade, on a moderate draft of 

 water. The best possible combination of good qualities— speed, 

 safety, accommodation and convenience of use— are to be had in a 

 yacht in which the greater part of the depth is made up by the 

 null proper, the keel or appendage being reduced to a minimum 

 Cfor the sake of light draft) and the mam factor of lateral resist- 

 ance being a centerboard properly proportioned to the hull and 

 placed in the one correct position. Could I say where this position 

 is, I should feerthat my work might aspire to a far higher value; 

 but I frankly confess that I know of no rule or formula that covers 

 the case, and there are many more experienced than I, professional 

 designers, who will join in this admission. Some designers do know, 

 but they are very few; some believe that they know, but their boats 

 speak to the contrary; many yachts of excellent proportions and 

 model have been utterly spoiled through the misplacing of the center- 

 board. AS in most of the details of yacht designing, the location of 

 the centerboard is not a matter of exact calculation, but of judgment 

 based on practical experiment and close observation. 



While I feel that what I have written is merely suggestive and by no 

 means as positive as it should be, I hope that it may still prove of 

 some practical value in pointing out the complicated nature of the 

 centerboard problem, and the great benefits which must result from 

 its satisfactory solution. 



A paper of special interest at the present time is that of Mr. James 

 C. McQuire, Associate, on the subject of "Aluminum; its Alloys and 

 their Use in Ship Construction. 1 ' 



The following extracts relate specially to the use of the metal in 

 yacht construction: 



Aluminum. 



The metal aluminum, as manufactured to day on a commercial 

 basis, is made entirely by the electrolitic process, this having sup- 

 planted the sodium process, which was discontinued on the introduc- 

 tion of the methods now employed in producing aluminum, for the 

 reason that the price at which aluminum is selling to-day is less than 

 half of what it sold for when manufactured by the sodium process, 

 and the users of aluminum have by no means seen the lowest figures 

 for which this material can be produced and furnished. 



The metal is very ductile, and can be rolled into sheets .0005in. in 

 thickness, and, if it;is desired, thinner than this; it is hammered into leaf 

 in exactly the same manner that gold leaf is hammered, and is used 

 extensively for decorating purposes, 



From the leaf the metal is ground into powder, which has its uses 

 not only for decorating purposes in the form of an aluminum bronze 

 paint, but is used in flash light photographing, and also very ex- 

 tensively in pyrotechnical displays, burning with a very brilliant 

 light. 



Aluminum is also drawn into tubes or wire, and is spun or stamped 

 into the different shapes. It is cast, drop-forged, ana in fact is used 

 in almost every way thH steel and copper is used at the present time. 



It is susceptible to a high degree of finish, by polishing or burnishing, 

 and becomes hard by working, or when being spun into shape, drawn 

 into wire, or stamped out. 



It is rendered soft again by annealing, and if required soft for a 

 final operation, such as stamping or spinning, it must be annealed be- 

 fore being subjected to this work:. 



By forging and cold rolling it can be given considerable rigidity and 

 temper. 



Aluminum is the lightest of commercial metals, a given bulk of it 

 being only one-third as heavy as a corresponding bulk of iron. 



The color of aluminum is very nearly the same as that of silver, 

 though instead of a dead white as in silver, aluminum has a delicate 

 purple tint. 



Next to the relative specific gravity which aluminum bears to other 

 metals, the resistance to oxidation is one of its marked qualities. 

 Pure aluminum does not tarnish from theinfluenceof weather, except 

 very slowly, even when exposed in a moist atmosphere. 



The action of salt water on pure aluminum is extremely slight, and 

 it withstands the action of sea water much better than iron or steel. 



Aluminum, however, does collect the barnacles, very much the same 

 way that steel does, although not quite so rapidly. 



A piece of copper and a piece of aluminum were placed on the side 

 of a wooden ship plying between New York and the West Indies, and 

 they were accurately measured before being put in this position, and 

 also after the ship returned. 



The copper, while free from barnacles, had lost ,097 of an inch, and 

 the aluminum, while the surface was covered with barnacles, had only 

 lost .005 of an inch in thickness. 



The more alloy which aluminum contains, the greater the action of 

 salt water upon it, especially those alloys of aluminum which contain 

 zinc. But more will be said on this subject later regarding the cor- 

 rodibility of aluminum. 



' * * * ~ ■ * ,<f *K ■ H 



The ordinary commercial aluminum is about of the same degree of 

 hardness as commercial copper, and, in fact, pure aluminum acts 

 very much like pure copper, as it hardens remarkably fast when being 

 worked either by forgiDg, hydraulic pressure, rolling, stamping, spin- 

 ning, or treated in some such similar way. 



One of the reasons that one hears it said sometimes that aluminum 

 castings are not strong enough to do the work is that people will ask 

 for pure aluminum castings, or buy the pure aluminum, and make 

 the castings themsslves; and, as previously stated, pure aluminum 

 does not make a very strong casting, and there is not one casting in 

 fifty which is ordinarily made of aluminum that should be made of 

 pure aluminum. 



There is just the same difference between an aluminum casting with 

 a few per cent, of alloy in it, and the pure aluminum casting, as there 

 is between brass and copper, and, excspt for special electrical work, 

 very few people would think of having a pure copper casting made. 



The difference in specific gravity between the pure aluminum and 

 the alloy is so slight that it is practically immaterial. But this subject 

 will be taken up more at length later. 



SPECIFIC GRAVITY, 



The low specific gravity of aluminum is probably its most valuable 

 quality, 



Ordinary cast aluminum is about 2.59, the sheet or worked metal 

 being about 2 76. 



The following is the comparative specific gravity, showing the 

 difference between aluminum and some of the most common of the 

 other metals: 



Aluminum castings 2.59 Cast iron 7,21 



Aluminum sheet, average 3.72 Wrought iron ...7,77 



Aluminum drop-forged or Soft steel 7. '87 



hammered 2.76 Copper 893 



Zinc cast. 6.86 Brass..,,. ., 8 39 



Zinc rolled 7.19 Nickel 8 80 



Tin 7.3 



From this it may be seen that the weight of a cubic inch of cast 

 aluminum is .094 pound, and the weight per cubic inch of rolled alum- 

 inum is .098 pound. 



It will also be seen that soft steel is three time.i as heavy as alumi- 

 num; copper is 3 6 times as heavy; nickel, 3.5 times as heavy. 



Silver is four times as heavy; lead, 4.8 times as heavy; gold, 7.7 

 times as heavy, and platinum, 8.6 times as heavy. 



The shrinkage of pure aluminum in casting is 17 B ,i of an inch to the 

 foot, to be exact; but it is generally taken, in making eastings, as Win 

 or about that of brass. The shrinkage of the nickel aluminum alloys 

 is much less and can be saftly reckoned as being only equivalent to 

 that of brass, 



Pure aluminum is very sonorous, and its tone seems to be improved 

 by using an alloy with a small percentage of silver, or copper and 

 nickel. r 



The best results can be obtained, in casting aluminum and its alloys 

 by melting the aluminum in the ordinary plumbago crucible, similar 

 to those which are used for melting brass or copper, and, if the metal 

 is not overheated, it will not absorb any appreciable amount of allicdu 

 from the crucible. 



Aluminum does not unite with or absorb carbon, under any of the 

 ordinary conditions, when the two are heated together. 



As previously stated, the metal is non- volatile at any of the ordinary 

 temperatures, and in order to prevent oxidation it is 'not necessary to 

 cover with any substance the metal which is being melted, 



A thin film of oxide will form on the surface of the metal when 

 melted, but it is not enough to injure the castings made from it as 

 this thin film protects the metal underneath from further oxidation 



In casting aluminum, practically the Sime rules should be followed 

 as in makiDg brass or bronze castings, 



E.ther sand or iron moulds may be used, the best result being de- 

 rived by using iron moulds; but, under certain conditions the alu- 

 minum blows away from the iron it this method of casting is not 

 properly understood and proper precautions taken. The best bicycle 

 castings are made in iron moulds, although the majority of the more 

 ordinary castings used in commerce are made from sand 



In making up moulds for casting aluminum, as large a gate and as 

 high a riser should be used as is convenient, for the reason that, in the 

 thin casting, one needs quite a head of metal to force the molten 

 metal to the most distant part of the moulds; and then, again, one 

 should have such a volume of metal in the gate that the casting 

 should grow cold before the gate gets cold, in order that, as the metal 

 in the casting shrinks, the liquid metal in the gate will flow in and take 

 it 8 place. 



The majority of unsuccessful castings made of aluminum have been 

 due to two causes, viz. : either the metal was overheated and poured 

 too hot. or the mould was not properly gated. 



Care should always be taken, in casting the alloys of aluminum, as 

 well as pure aluminum, that the temperature of the mass is not raised 

 too high; for, if the metal is overheated, it will absorb gases, which it 

 will not do if not raised very much above the melting point; and, 

 again, in the case of the alloys, if the temperature is not carefully 

 watched, some of the hardening ingredients will be burnt out, as is the 

 case with zinc, which melts and volatilizes at a lower temperature 

 than that at which aluminum melts. 



Another point which it is desirable to observe in making castings 

 from the alloys is to keep the metal thoroughly stirred from the time 

 it gets into a molten condition until it is finally poured; for, if this is 

 not done, tha tendency to burn out some of the hardening ingredients 

 will be greater, and also some of the heavier ingredients will settle to 

 the bottom and collect; thus, when a series of castings is being poured 

 from the same crucible, one will not get them all of a uniform degree 

 of hardness. 



After the metal is removed from the fire it is a good principle to oool 

 it down with some new metal before casting, in order to be sure that 

 it is not being poured too hot. 



This is generally done by taking an old gate and stirring the liquid 

 metal with it, allowing the gate to melt as you stir. 



It is a matter of but very little experience to tell by the eye when it 

 Is cooled down to the proper temperature for pouring, since, as pre- 

 viously stated, the metal should be poured as cold as possible, In order 

 to have it flow freely and get the best results. 



The best alloys of aluminum are made directly; that is, the alloy is 

 produced and combined with the aluminum in the furnace at the same 

 time that the aluminum is produced, which is one of the great secrets 

 in making a successful alloy. 



The consideration of the aluminum bronze, and the casting of it, 

 would require a treatise in itself, aud the author of this paper will not 

 go into this subject or take up any of the alloys of aluminum on the 

 other end of the scale— that is, where the percentage of aluminum is 

 small as compared with the other ingredients present. 



ANNEALING. 



After the aluminum ihgotB have been east and rolled into sheets, 

 there are many cases where it is necessary to anneal the aluminum 

 before the rolling is carried further, as is the case' when the sheet is 

 desired soft for stamping or spinning. 



This process of annealing is accomplished by heating the aluminum 

 sheets in a muffled furnace to such a degree of heat as would raise a 

 piece of steel to a dull red, which is in tha neighborhood of 700° Fahr., 

 great care being taken that the aluminum is thoroughly heated 

 through, aud not only on the surface. 



There are many ways of telling when the sheet or wire, as the case 

 may be, has been annealed through, as its temperature varies accord- 

 ing to the form of the piece or thickness of the sheet being annealed. 



But for ordinary purposes take a pine stick, and if, when drawn 

 across the sheet of aluminum which has been heated, the stick is 

 charred and leaves a black mark behind it, the metal is sufficiently an- 

 nealed to proceed with further operations on it. 



After removing the metal from the muffle, it should be allowed to 

 cool slowly. This is accomplished in many different ways. 



The question of rolling aluminum is one of extreme simplicity, and 

 requires but little practice on the part of mill men to roll successfully. 



Most of the heavy Ingots when starting to be rolled are heated and 

 rolled at a low annealing heat, and there is only one principal feature 

 in which aluminum differs from copper in rolling, and that is that it 

 hardens up very quickly when being rolled— much quicker even than 

 either steel, brass or copper— and the metal has to be annealed for the 

 successive operations, according to the degree of hardness which is 

 desired in the finished sheet; and, also, if an alloy of aluminum, on 

 the percentage of alloy which the sheet contains; the sheet contain- 

 ing the largest percentage of alloy requiring the most frequent an- 

 nealing. 



If this annealing is not done, and the sheet contains much alloy, or 

 is rolled thin, it will crack in the rolls. 



Ordinary hand-rolled aluminum, which is rolled as much as possible 

 after annealing, is about as hard as the ordinary hard brass. 



Of course, when the ingot or sheet goes to the rolls from the an- 

 nealing furnace, you can take a larger draft with youn rolls than you 

 can later, when the sheet begins to get thin., and also hard from being 

 worked; the draft of the rolls then has to be reduced considerably 

 from the amount first used on the sheet, just after coming from the 

 furnace. 



Aluminum is susceptible of taking and retaining a very high polish. 

 All metals exposed to the influence of moisture will become soiled or 

 tarnished and require polishing to a greater or less extent. 



In the case of aluminum, although the actual oxidation on the sur- 

 face of the metal is practically very slight, yet, if the metal is not 

 cared for, there will, to a limited extent, be a certain amount of oxida- 

 tion taking place. 



It is therefore as necessary to clean aluminum by polishing it now 

 and then as it is to keep other metals clean. 



The oxide of aluminum is a white powder, which forms in a thin film 

 on the surface of the metal; and as long as this nlru is not broken or 

 removed, and since the oxide of aluminum itself is insoluble, this coat- 

 ing of oxide forming over the surface prevents, to a certain extent, 

 further oxidation of the metal. But, as a matter of fact, it is practi- 

 cally impossible to keep this oxide from being broken or disturbed. 

 If, however, the oxide is removed from the surface and the metal is 

 kept well polished, it will be found that the oxide forms much more 

 slowly on a smooth surface, which has been well poli3hed, than on a 

 rough surface, or one that has been scratched by using a polish not 

 ground fine enough; these in finitesims.1 crevices collect and hold the 

 moisture in the atmosphere, which will attack the metal with greater 

 rapidity than on a smooth surface, and it is for this reason that the 

 greatest care should be used in selecting for this work a suitable 

 polish, the chief merit of which consists principally in being ground 

 fine enough. 



Any of the polishes used for polishing brass and other metals and 

 fulfilling the above requirement will polish aluminum, and with very 

 much less work on the part ot' the user than is necessary in keeping 

 othef metals clean; the reason for this being, as above stated, that the 

 oxide of aluminum which first forms, b.^ing insoluble, the surface of 

 the metal, when once covered with it, retards the progress of further 

 oxidation to a large extent, aud further destruction of the surface 

 continues but slowly. In the case of nearly all metals except alumi- 

 num the oxide is soluble in water, and consequently, after the mois- 

 ture has penetrated the oxide, the corrosion continues as badly under 

 the first coating as it did when the metal first began to corrode. 



Where oxidation or corrosion of aluminum is liable to take place, 

 due to its exposure to the action of alkalies or acids that aitack this 

 metal, it has been found that polishing tha metal after its exposure 

 reduces very largely the effe«ts of corrosion, which, when once seri- 

 ously started upon the metal, seems to act in a sort of continuous 

 manner, especially if this starting has been caused by chlorides or 

 alkalies. 



If the people who use aluminum in places where they want it to 

 stay bright, or expect it to look nice and clean all the time, will expend 

 a small portion of the energy and time to keep their aluminum bright 

 which they would on the same article made of other material, they 

 would find that their efforts would be well rewarded, and that the 

 work necessary to keep aluminum bright is infinit esimal when com- 

 pared with that required in keeping other metals bright. 



The best polish, probably, for aluminum is the Acme Aluminum Pol- 

 ish, one of whose chief merits, however, as above stated, consists in 

 its being ground extremely fine. 



A great deal of harm has been done aluminum by the reports of 

 people not familiar with its non-tarnishing and non-corroding prop- 

 erties. 



If this was properly appreciated, and people would expend the neces- 

 sary amount of effort to keep it clean, it would soon find its place for 

 many uses, for which at the present time the public at large think it 

 undesirable or unsuited to the purpose in question. 



In conclusion, keep your aluminum painted or keep it clean, if ex- 

 posed to moisture or corroding influences. 



The question of welding aluminum is a very simple one, and the 

 metal can be welded on any electrical welding machine. 



It caunot very successfully be welded by other means than that of 

 electricity, for the reason that it conducts the heat so rapidly that the 

 surfaces get chilled before the union takes place. 



When this welding is done by the passage of an electric current, 

 however, the heat is maintained while the surfaces are being brought 

 together until the union is effected. 



This method is used principally for joining wire, and in the manu- 

 facture of bicycle tires and similar work. 



The question is often asked: "Can aluminum be soldered?" The 

 reply is that it can be soldered, but it is difficult to do, the principal 

 reason for this being that it is with difficulty that solder can be made 

 to adhere to aluminum, since the heat conductivity of aluminum is so 

 great that as soon as the solder comes in contact with the metal the 

 heat is conducted away from it so rapidly that the solder is chilled, and 

 will thus not be allowed to flow freely on the surface of the aluminum. 



This can be overcome to a certain extent by keeping the sheet heated 

 with an alcoholic lamp or a gasoline torch while the soldering process 

 is beinf carried on, 



There are two general methods of soldering. One is to prepare the 

 surface of the sheet chemically, so that the solder will form a chemi- 

 cal combination with the surface so prepared, and adhere; and the 

 second method is to plate with copper or some other metal the surface 

 to be soldered, and then Holder together these two surfaces. 



The difficulty in this latter method is that, unless the plating is car- 

 ried on with unusual care and skill, the plating itself will not adhere 

 to the surface of the aluminum after a period of six or eight months 

 and the surfaces will drop apart, not from the fault of the solder, but 

 from the fault of the plating. 



Too much care cannot be taken, especially in using aluminum 

 around water, salt water in particular, to prevent oxidation by gal- 

 vanic action. J * 



Aluminum stands well at the head in the table of metals arranged In 

 electro chemical series, thus showing it to be very much more positive 

 a. ? £ e otber 01 'dinary metals, which stand much lower in the table. 

 And when two metals are ia contact, especially in salt water, a voltaic 

 couple is formed, which is equal to the sum of the electro-motive forces 

 between the metals, and when such a couple is formed the most posi- 

 tive element is the one that is attacked the more severely. Aluminum 

 naturally suffers the worse, as it is electro-positive to the ordinary 

 metals of commerce, and shows up badly in comparison. 



This subject of galvanic action was investigated very thoroughly by 

 Mr. Yarrow, who constructed the first torpedo-boat for the French 

 Government, He was not able to obtain aluminum rivets which were 

 strong enough to satisfy all the conditions which he thought would be 

 met with, and he was afraid to use copper or composition rivets for 

 the reason that aluminum and copper, or composition, stood so far 

 apart m the table of electro-chemical series. 



So housed iron, which stands closer to aluminum than any other 

 metal from which it would be possible to make rivets. 



These rivets have given entire satisfaction, as far as strength and 

 corrosion of aluminum and galvanic actiou are concerned, but some 

 objection has been found to them for the reason that, the paint to a 

 certain extent is porous, and a slight amount of corrosion has taken 

 place on the heads of these rivets; in other word-i, there has been 

 formed a composition of alumina and i''on rust, which has run down 

 and discolored the sides of the boat, so that, iu order to keep this boat 

 looking nice, the Government has had to keep it well painted, in order 

 to prevent the iron rivets from rusting. 



This question of riveting came up when the Defender - was construct- 

 ed, aud the advice of the author of this paper to the builders was to 

 use aluminum rivets, and he offered to furnish these of the same 

 character and grade of material as that from which the plates were 

 constructed. 



The author was informed by the manufacturers that they did not 

 have time to investigate the strength of these rivets thoroughly and 

 pending such investigation they would u^e bronze rivets, 



He argued against this, and advised using an iron rivet, or an iron 

 rivet galvanized, in order to minimize galvanic action. This advice 

 however ; was not listened to, and the boat was constructed with' 

 bronze rivets. It remains to be seen how the plates around these 

 rivets are going to withstand the galvanic action. 



Even in using bronze rivets in the boat above referred to, the effect 

 of the galvanic action could be materially reduced by coating the 

 inside of the holes with white lead, and then dipping the rivet in white 

 lead or paraffiue before driving. But this was not done. 



It was also advised that where the aluminum plates joined the bronze 

 plates they take a strip of heavy canton flannel and soak it well for 24 

 or 36 hours in white lead, and then place this strip between the plateB 

 as lapped, and rivet up with this canton flannel, soaked in white lead 

 between the edges of the two plates, as a "neutral joint." This was 

 not done either. 



From the results of experiments abroad, the practice seems to be 

 that it is almost necessary to use aluminum rivets in riveting together 

 sheets of aluminum, especially where it is to be used in and around 

 salt water. 



The author agrees with this theory entirely, and does not think that 

 too much stress can be put upon the necessity of using rivets of the 

 same material as the plates, and he also believes that foreign gov- 

 ernments have experimented and gone far enough into the subject 

 of aluminum for ship construction to know what is best. They have 

 certainly done more in this line than has been done in the United 

 States, and the results of their experiments cannot be profitably 

 ignored. J 



It is a fact, however, that aluminum used as a rivet does not give as 

 high a value in shearing, iu proportion to its ultimate tensile strength 

 as is obtained by comparing the shearing strength of steel and its ulti- 

 mate tensile strength. 



The ultimate shearing strength of the ordinary commercial struc- 

 tural steel in comparison to its ultimate tensile strength is about as 

 7.5 is to 100, while the experiments that the author has made on the 

 shearing value of aluminum in comparison with its ultimate tensile 

 strength are about as 60 ia to 100. 



This only means that one has to use a proportionately larger rivet 

 in riveting aluminum plates together with aluminum rivets than one 

 would use in steel rivets in riveting steel plates together. 



When this is looked at in the right way, it is a very simple matter to 

 determine the proper area of the rivetB to be used in proportion to 

 the thickness of the plates to be riveted: therefore the strong advice 

 of the author to constructors contemplating the use of aluminum 

 plates is to use aluminum rivets also, which can easily be done In 

 spite of the low unit strain of aluminum rivets in shear. 



Aluminum will form a natural alloy with nearly all of the more 

 ordinary metals except lead, antimony and murcury. 



The most common alloys, however, are those with copper, nickel, 

 zinc, manganese, silver, chromium and tungsten. 



The useful alloys of aluminum with these metals, generally speak- 

 ing, do not exceed 12 per cent, or 15 per cent, on either end of the 

 scale; that is, if the predominant metal is aluminum, the ailoy will 

 not exceed 12 per cent, or 15 per cent., in order that it may impart 

 useful qualities to the aluminum. A greater percentage of alloy than 

 this seems to make the metal either hard or brittle, or impart some 

 other quality which does not add to the commercial advantage of the 

 metal produced. 



On the other hand, if the principal ingredient is one of the metals 

 above named, and aluminum is used as an alloying metal, the quality 

 imparted is always an improvement on the predominating metal up to 

 any percentage not exceeding 12 percent, or 15 percent, of aluminum 

 Beyond this point you work into the same state of affairs that you do 

 on the other end of the scale as described above. 



The grade of aluminum used In Defender is what is known in the 

 market under the commercial name of "the Pittsburg Heductiou Co.'s 

 nickel aluminum." 



After a great deal of experimenting on the part of the manufac- 

 turers, it was decided, after taking all questions into consideration, 

 that this was the most satisfactory alloy to use. 



The alloys that were under discussion were those of copper, zinc 

 nickel and chromium used individually; experiments were alBo made 

 by using one or more of these ingredients in the same mix; and, after 

 conducting a large series of experiments, the above alloy was chosen 

 for the reason that it possessed more advantageous qualities than any 

 of the others seemed to possess. 



The alloys of copper have been used for this purpose abroad, and 

 seemed to have given satisfaction there, but the results of experiments 

 conducted previous to getting out this sheet seemed to show that the 

 use of per cent, copper, which is what Yarrow used in constructing 

 the torpedo-boat which he built for the French Government, did not 

 give an aluminum sheet which was either as strong or as ductile aa 

 that from which the plates above referred to were made, 



The plates and angles used in Defender are the largest ones that 

 have ever been rolled, and it can be positively asserted that the suc- 

 cessful achievement of furnishing these plates marks a new era not 

 only in yacht construction, but in the possibilities which are offered 

 by future developments in the arts aud manufactures for material 

 which possesses the unusually high qualities of that which was fur- 

 nished for Defender. 



The plates used in Defender vary from 14 to %\n, ia thickness, the 

 majority of them being 5 18 and %. 



She is constructed of aluminum plating from her waterline up, 

 which amidships gives an aluminum belt a little over 4ft. wide. 



Her deck beams are of aluminum, being composed of 5in. bulb 

 angles, being 5iu. on one leg and 2>£in. on the other, 5 , 3 iu. thick, weigh- 

 ing in aluminum 3J-*jlbs. to the foot. 



These angleB were made from the same grade of material as was 

 U6ed iu the plates. 



All of the lateral and diagonal braces under the deck are aluminum 

 plates about %ia. thick. There is also an aluminum stringer plate, 

 about 2ft. Oin. wide, which connects the deck beamB with the side of 

 the vessel, aud is continuous throughout the length of the vessel. 



The rail of Defender is also composed of a 5in. bulb angle of the 

 same size as described above, the 2^in. flange being riveted to the 

 stringer plate above described, aud'the 5in. leg having the same level 

 as side of the vessel at the point where the two join ; from this it will 

 be seen that at the stern of the boat it was necessary to open this 

 angle out until the two flanges were almost in a straight line. This 

 was done without any sign or fracture on the inside of the angle. 



The dead-light frames and covers which are placed in the deck are 

 also constructed of aluminum, as well as the lanterns, and also many 

 of the small interior fittings. 



Her blocks are of wood, with aluminum sheaves, and they have given 

 great satisfaction, the sheaves being stronger than those constructed 

 in a similar manner, which were used on Vigilant, these latter being 

 made from composition and wood. 



