Monday, November 21, 2011

An Abandoned Planking Method

It may seem out of place to examine the shipbuilding methods of the ancient Greeks and Romans in a blog whose subtitle is "small craft outside the Western tradition," given the fact that so much of Western culture is directly descended from those early civilizations. But the boatbuilding methods they employed ultimately went nowhere -- they died out and ended up contributing little to the boatbuilding traditions that we currently recognize as Western.

"Traditional" Western boatbuilding is characterized by one of two planking methods: carvel and clinker (or lapstrake). Carvel is the smooth-skinned method of planking, with the planks set edge-to-edge and attached to a pre-assembled framework. In clinker boatbuilding, each plank overlaps the one below it. Clinker construction proceeded shell-first. That is, after the keel, stem, and sternpost were assembled, the planks were fastened to one another, after which the ribs and other internal stiffening structures were installed. (Some modern artisan builders of lapstrake boats set up a complete temorary framework before planking.)

The ancient Greek and later Roman method differed from both of these. Planking was laid edge to edge, for a smooth skin like a carvel hull's. But construction proceeded shell-first, as in clinker construction. Most interesting was the method used to fasten the planks to one another.
A section of plank recovered from an ancient Greek shipwreck, showing tenons on both edges. Note how they overlap in places. From Lionel Casson: Ships and Seamanship in the Ancient World

Left: schematic showing the method of mortise-and-tenon joinery, with pegs to fix the planks to the tenons.
Right: a plank recovered from an ancient shipwreck, split down the middle, shows how a large percentage of the plank was taken up by the mortises and tenons.
Both images from Lionel Casson: Ships and Seafaring in Ancient Times
As can be seen in the images above, both edges of the planks were deeply mortised, and held in alignment by free tenons. The planks were then drilled through the tenons at both of their ends, and tight-fitting dowels were driven through the holes to hold the tenons in place.

In this amazingly labor-intensive fastening method, the mortises took up a large percentage -- often more than 50% -- of the length of each plank's edge. Sometimes, the mortises were staggered alternately toward the inner and outer faces of the plank, so that they actually overlapped, thus totalling more than 100% of the length of a plank's edge.

Having been used for thousands of years in trade, war, and explortation, it could hardly be said that this method of shipbuilding was a failure. But it was ultimately superseded by methods far less time-consuming to employ. The clinker method was developed in Scandinavia. The source of the carvel method is subject to dispute, but it appears to have originated in the Mediterranean independent of the Greek and Roman tradition. Both ultimately overlapped in northern Europe and made their way to the Americas.
Proposed construction cross-section of a Greek two-level fighting ship. This ship would have used the mortise-and-tenon planking method described here. From Lionel Casson: Ships and Seamanship in the Ancient World   

1 comment:

  1. The "Celtic" planking method was another "carvel" construction system described by Julius Caesar about the Veneti ships.

    Thick nails driven through carvel planks into heavy timbers, not ribs, then turned over and driven back into the timber. Planks not fastened to each other although caulked.

    Full exposition of a find in "The Barland's Farm Romano-Celtic Boat", Nigel Nayling and Sean McGrail 2004.

    See also the illustarations on Navis for the construction of the Blackfriars Ship, another example.