52 NAVAL SCIENCES. 



sometimes also a second yard at the jib-boom, which corresponds in size 

 with the main-top-gallant-yard. 



The flag-staff is the pole which bears the great national flag; it stands 

 in a cap at the centre of the tafTrail, inclining back in the direction of the 

 stern-post. On its truck there is a sheave for the line by which the flag is 

 hoisted and lowered. The flag-staff" is one eighth longer, but one fifth less 

 in diameter, than the main- top-gallant-yard. 



The fore-flag-staff stands on the cap of the bowsprit, and is four fifths of 

 the length, and three fourths of the thickness of the jib-boom. The top of 

 the staff' has a truck with a sheave to hoist the flag (pi. 25, fig. 1). In more 

 recent times the main flag-staff* has been set aside for various other arrange- 

 ments, and the flag is raised by a tackle at the peak. 



Besides the spars already mentioned there are several others ; for example, 

 the studding-sail-yards, used to lengthen the yards for the addition of stud 

 ding sails, studding booms, &c. ; but as they are only used in a light wind, 

 they are generally kept with the spare spars. 



2. Rigging and Tackles. The rigging and tackles are so closely con- 

 nected, that it will be more convenient to describe them together. By 

 tackle-work we understand the blocks and fixtures through which the rigging 

 is rove, and on which it is fastened. 



A block (pulley) is a mechanical contrivance which is used in various 

 ways on ship-board, consisting of a shell or outside, one or more sheaves 

 or wheels, on which the rope turns, and a pin or axle, for the sheave. 

 The diameter of the sheave is six times its thickness, and this varies with 

 the size of the rope for which it is grooved on the circumference. In the 

 centre of each of the outer sides of the block is a groove, around which 

 passes a short rope, called a strap, or an iron band with a hook. The blocks 

 have a variety of names. Mortised blocks are made of a single block of 

 wood, mortised out to receive a sheave. All blocks are single, double, 

 triple, or fourfold, according to the number of sheaves contained within the 

 shell. There are some blocks which have no sheaves, used to receive the 

 ends of ropes, as hearts, bulVs-eyes, dead-eyes, &lc. Fig. 14* is a single 

 strap-block, j^g-. 13 a threefold cat-block, ^^. 15^ a fourfold tackle-block, 

 fig. 11a block for the arm of the main-yard, fig. 14^ a top-mast dead-eye ; 

 fig. 16 a block with a swivel-hook ; j^^. 12 a strapped twin block, and fig. 15* 

 a tail-block. 



If a rope turn on only one sheave, so that the weight is at one end and 

 the power at the other, the purchase is called a whip. Two single blocks 

 form a gun-tackle purchase ; a single and a double block form a luff-tackle 

 purchase ; fig. 8 is a luflf-tackle connected with a runner, which is a rope 

 rove through a single block, hooked to a thimble in the eye of a pennant; 

 fig. 9 represents a winding-tackle rove in threefold blocks. 



The tackles have different names, according to their place or their ser- 

 vice. PL 22, fig. 6, shows the davits with a lifting-tackle drawing up a piece 

 of cannon. The quarter-tackles hang on each side of the mast, and together 

 with the yard-arm tackles serve to hoist up boats, provisions, and other 

 heavy articles. The yard-arm tackles are fastened to the yard-arms, and 

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