statcounter code

Wednesday, December 12, 2012

Scarf Joints: Essential in Shipbuilding

In building full-size wooden ships, it is impossible to get wood timbers long enough to make some of the structural members. In these cases, several pieces are joined together lengthwise by "scarfing": tapering the ends, lapping them and then fastening the two together.

shipbuilding, construction, ship, wooden, wood, scarph, joint, model
Types of Scarphs - illustration from
The Construction of a Wooden Ship
by Charles G. Davis
As Charles G. Davis notes in his book The Building of a Wooden Ship:

Scarfing timbers together is one of the most important processes in wooden shipbuilding and deserves detailed explanation.
The length of the scarf is shown in the plans or specifications and is usually given to the workmen by the foreman who lays out the work. The foreman also tells the workmen the depth to make the pointed end or nib, as it is called, but if he does not, 23 percent, or about one-fifth the depth of the timber, is a safe rule to cut to.
Care must be taken not to run the saw out any deeper so as to make a weak spot where the timber may split when bent. The scarf is first marked out on the timber and is then sawed out on a band saw or circular saw. If neither is available a 5-foot or 6-foot cross-cut saw may be used and several saw cuts made and the chunks of wood spilt, chopped, or dubbed out with a broadaxe. The timber is then trimmed or dubbed off. carefully to the line on the face or working side of the timber with an adz. The remaining wood is then worked off, using the carpenter's square frequently to see that too much is not cut away. The face of the scarf is finished off with a plane so that the carpenter^s square fits perfectly on its face when applied at various points across it.
There are several kinds of scarfs; the plain scarf, flat scarf, hook scarf, lock scarf, etc. The plain and flat scarf are the ones most commonly used and the hook scarf comes next. The lock scarf has an opening in which is driven an oak wedge or key for the purpose of keying and setting the ends of the scarf tightly together. The keel scarf with tenons is a combination of the plain and hook scarf and is more difficult to cut and fit. To prevent pulling apart short wooden pins, called dowels, fitted vertically in the face of the scarf, were formerly used, but nowadays the more common practice is to bore across at the seam where the two faces meet and drive in treenails, long wooden pins about the size and shape of broom handles and usually made of locust wood. Sometimes a better fit can be obtained by running a cross-cut saw through the joint. When the surfaces fit perfectly with their nibs or ends pushed tightly together by means of a jack at one end, they are either clamped together with big iron screw clamps or are wrapped with chains with wedges driven between the chains and the timber so as to draw the wood tightly together.
Vertical holes are bored and iron or steel clinched fastenings and treenails are driven by the use of compressed air tools — air drills and air hammers. In some yards electric drills are used. Where air or electric tools are not provided the holes are bored with hand augers and the dowels and treenails are driven by sledge hammers. 

These strong joints are also useful in model ships, so it is a good idea to learn how to create them in miniature.

No comments:

Post a Comment