46 NAVAL SCIENCES. 



back of the lower part there is another piece of timber, shaped like a wedge, 

 with the point turned upwards. To this is attached a third piece of similar 

 form. They both reach only to the surface of the water. The upper part 

 of the timber passes through the helm-port. There is a square hole in the 

 rudder-head, through which the tiller passes which turns the rudder. As 

 the tiller exerts a great power, it cannot be worked by hand. Two ropes 

 are, therefore, attached to its forward end, running on blocks along the two 

 sides of the ship. These are called tiller-ropes. They pass in opposite 

 directions over an upright wheel, with hand-spokes. As the wheel is 

 turned, one rope winds, while the other unwinds. The rudder is thus moved 

 without difficulty, and its position can be ascertained every moment by the 

 tiller rope. In large ships of war, double wheels are in use {pi. 21, Jig. 2). 

 4. Rules for Ship-Building according to Seppings's System. All 

 the timber should be thoroughly seasoned. The tenons of the timbers 

 in the largest ships should never be less than three inches thick. Where 

 timbers are to be joined together, at least two l^^-inch bolts must be used. 

 If seams should appear, on account of the timber not being thoroughly 

 seasoned, they must be closed up with great care. It must also be provided 

 that every seam should lie higher on the outside than on the inside, so that 

 if the water should get in, it may flow off towards the inside of the ship. 

 Seams of more than three inches in width are to be filled with pieces of 

 timber consisting of old oak, and altogether free from sap-wood. The 

 fibres must run parallel with those of the timbers which are to be closed. 

 Seams of less than three inches in width are filled with double wedges, 

 driven at the same time on the outside and the inside of the ship. The 

 front of these pieces while drying must be dressed with oil and tar ; for this 

 purpose, small holes are often bored in their head and oil poured in. PL 9, 

 Jig. 6, shows a seam closed up at A, an opening of less than three inches 

 at B, and an opening of more than three inches at C. D is a filling with 

 wedges, the fronts of which are both inside and outside ; E is a usual filling 

 where the fronts appear above and below ; F are seams which must be 

 caulked. All the planks are to be fastened to cross-pieces, as in Jig. 7, their 

 joinings being made to correspond. The clamps are secured to the frame- 

 work in the same manner, with the addition of vertical bolts, as in Jig. 8. 

 In order to bring the diagonal timbers as near as possible to the supporters 

 under the frame-pieces of the gun-deck, a corner of six inches may be taken 

 from the bottom of the beam of the upper course, as in Jig. 9. If frame- 

 pieces for the upper deck of sufficient breadth are not to be procured, we 

 need not hesitate to join the sides of the timbers, so as to form a wedge- 

 shaped piece connected by double notches, as in Jig. JO. In order to avoid 

 the accumulation of water on the upper side of the water-ways, they must 

 spread in from the timbers so as to lie deeper than the connecting pieces, 

 as in Jig. 11. The joinings of the water-ways must be so arranged that 

 they will fall on the centre of the kelson, and that the descending part of 

 the channel below the joining shall be in the direction of the side of the 

 beam, as in Jig. 12. The diagonal seams under the water-ways must be 

 thoroughly caulked, for which purpose the curved iron stoppers are used, 

 698 



