 |
 |
||||||||||
|
|
|||||||||||||
| Content |
George F.Campbell
"China Tea Clippers" |
Page60 | ||||||||||||
The main
trouble was that the mixture for the copper alloy was not consistent
throughout, owing to imperfect manufacturing methods, and the sheathing
nails themselves could be different, which meant that the deterioration
of the plates was piecemeal, a condition which was aggravated
progressively as the plates were renewed piecemeal also. Another cause
of plate deterioration on fully wooden hulls was puckering, and the
loosening of nails due to the twisting movement of the hull when riding
diagonally across heavy seas. Such movement could be considerable,
opening up seams on the weather side and compressing them on the lee
side.The copper plates could be nailed directly to the planking over a tar or pitch coating, or in the best work over tarred paper or felt about 1/4 in.thick. After nailing, the plates were hammered down along the exposed edges until hand smooth. The nails sometimes were hammered so that they gave a quilted effect to the sheathing, but this was considered bad practice. The varying sizes of plates and their relative positions are given in drawing (44) which shows naval and merchant ship practice. Very small craft would use smaller plates. Although the ideal system of laying the plates was to have the exposed edges of the butts facing aft, and those of the seams on the lower edge, this arrangement helping to keep a loose plate reasonably flat by gravity and water flow, it was only achieved on very small craft where probably a single gang of workmen would work progressively in one direction, as a modelmaker would plate a model. However with a large ship in drydock or on the slip this would take too long, and several gangs would be working together, some from amidships towards the bow or stern and some from the waterline downwards or keel upwards. This would mean that the exposed edge of the seams and butts would vary in their relative positions on different parts of the hull, which can sometimes be seen on contemporary photographs. With multiple gangs the shipwright would have to mark off the run of the plates carefully. The areas where gored strakes were necessary would be useful for meeting points. The standard rectangular plates were cut as little as possible, which meant that on certain hull forms the uppermost strake was not always continuous or paralleJ from stem to sternpost. If the top edges of the uppermost strake were necessarily cut to form the waterline the discarded pieces would be used as far as possible to form the gores elsewhere. The waterline for the coppering was not a true horizontal but had a gentle sheer to it, as was done with all waterlines, whether painted or coppered. It would be approximately 18 in. above the load waterline aft to 30 in. forward and drop to 12 in. amidships, on a large clipper. The appearance of the copper, varying slightly with the composition from reddish to yellowish, would be like an old copper coin, when it was freshly applied. At sea in salt water it would be bright and shiny, and in port or drydock alight green when dry, like a copper dome. An eye-witness in the mid-19th century gives a most thrilling description of a naval squadron under full sail in the Channel, majestically rising and dipping in the swell with the wet copper glinting and flashing in the setting sunshine. |
||||||||||||||
| |
||||||||||||||
