Clinker Boat History & Building

Historical Background

This method of constructing a watertight boat shell is thought to have originated somewhere in central Asia and travelled with its original inventors as the ice retreated and they migrated to the shores of the Baltic via the great rivers of Russia that feed into it. The early settlers in the recently ice-free countries of Scandinavia had a great need for boats. The nature of the country, mountainous, and cut by fjords and narrow arms of the sea made water the most practical form of transport. Marine Archaeologists have found very few remains of these very early craft, the perishable nature of their materials has meant that only in very unusual circumstances has anything survived to the present day. What has survived shows that the fundamental principles have changed little in two thousand years.

The clencher method of construction makes a hull very stiff for its weight and requiring only the simplest tools to build it. An Axe, wedges for splitting logs, a hammer for clenching nails and a primitive bow drill are all that are necessary to construct even the most advanced of the type, the Viking Longship. We are fortunate in having several well preserved examples of this final perfection of technique so that we can see how little it changed over the centuries. These craft were specially built to act as enormous coffins for Nordic Royalty and since they where carefully buried they survived more or less intact.

Clencher built boats of which there where several types dominated the Northern seas from Iceland and Greenland to the English Channel some travelled even further afield in the hands of the Viking corsairs who used them for their grander raids, doing the whole circuit of Europe. First south via the Bay of Biscay, through the Straits of Gibraltar and then along the coasts of the Mediterranean, raiding as they went. Through the Dardanelles and the Black Sea and finally home via the Russian river system. The light weight of the boats making the portages necessary at the heads of the rivers practicable. The method lived on well after the Viking era and clenched planking has been found on larger vessels used for trading in Northern waters. The Bremen Cog is an intermediate type with clinker side planking and a caravel bottom. Some northern Carracks where also built in this manner, and their images, the plank edges clearly visible, are preserved on the seals of many ancient ports. With the eventual adoption of the frame first method of construction for larger wooden hulls clenched planking survived as the preferred method for making smaller boats and inshore fishing craft. Its ability to be prefabricated from ready cut parts made it the ideal system for the shallops carried by the larger ships of the Age of Exploration. Carried in the hold as a Do-It-Yourself kit they could be rapidly assembled by the ships carpenter to augment or replace the ships complement of small boats.

Materials

The relatively thin planking of this type of hull means that only the most stable timbers can be used. In Europe, Northern Larch is preferred for the larger working boats where the plank thickness exceeds half an inch. For lightweight sailing dinghies with plank thickness of only five sixteenths of an inch or so only South American mahogany is stable enough to be truly satisfactory. Worries over the destruction of the Amazon forests in recent years has lead us to take great care that we only obtain our timber from legal sources and that all its documentation, certified by the Brazilian Government, is in order before it is delivered. The ribs, or more correctly the timbering, in these boats is local English oak, only partially air dried and then steamed into shape. The further curing of this timber in the boat tensions the structure adding to its stiffness. The gunwales and rubbing strakes are made from a tropical hardwood called Iroko. This timber comes to us in logs sawn into planks two inches thick the full width of the tree and this we convert to sided timber making the best use of each piece. This timber is widely distributed in both Africa and the Far East, we normally get ours from The Cameroon in East Africa. The hull is fastened with copper boat nails, square in section "clenched" i.e. riveted, over roves, the conical washers, and this system gives the method its name. Originally the Scandinavians used soft iron nails with diamond shaped flat roves, however the use of copper has been universal for a very long time since it does not rust or react chemically with the oak timbers. Finally the plank "lands" are sealed with a small amount of a synthetic rubber compound. This replaces the horse hair and "Stockholm Tar", a resinous pitch distilled from pine wood and much used by the old boatbuilders.

Stages of Construction

A considerable stock of timber is always maintained as we like it to stabilise before we use it. Timber after it is freshly sawn has wide variations of moisture content due to the uneven drying of the log. A few months stacked interleaved with drying battens prevents distortion and uneven stresses in the final boat.

Drafting

The basic design of the boat is first "lofted" on the floor to get the general layout and to enable the "molds" to be made. These form a framework on which the shell of the boat is finally built. These moulds are then set up and battens run round them to represent the edges of the hull planks, at the same time the hull shape is viewed from all angles to confirm the final shape. It is very unusual for

Half-Model

there to be no modifications at this stage. I generally lie on the floor under the boat visualising the water flow as the boat heels, trying to get a clean run without undue distortion of the waterplane area. Once confirmed the moulds are adjusted and the plank edges marked. All the timber is then cut and planed, the transom shaped and the keel, hog and centerboard case fabricated. These are then trued up on the building beam to form the spine of the boat.

The moulds are then put in place and planking can begin. Each plank is first rough cut from the timber stock which is thick enough to allow it to be split into two halves to form a pair of identical planks.  This is important in a varnished boat since it means that the planks on either side will have similar depth of colour and grain. The two halves are then planed to the final thickness ready for the next stage. Each plank is finished by hand to the final shape, the edges planed so that it fits snugly against the plank below and the "jerrolds" cut in the ends with a chisel so that each plank fairs in smoothly at the stem and transom. This is probably the most skilled part of clencher boat building since on it depends the water-tightness of the final hull. Unlike virtually all other forms of woodworking there are no straight edges or constant bevel angles, all change constantly along the run of the plank and it takes considerable experience and practice to do this part of the job both quickly and well. When fitted, the plank is steamed in a steam box to soften it. While it is hot it is clamped into position and then nailed to its predecessor. A "dolly" is used to support the head of the nail while the inside is clipped off to length and then riveted over the rove with a ball-pean hammer. To plane up, fit and fix two planks is considered to be a reasonable days work. Once the hull has been planked up the molds are removed and the inside sanded and given three coats of varnish. This is to ensure that the hull is protected under the timbers. When the varnish has hardened the timbers are steamed in and then nailed in position in the same manner as the strakes of planking. This completes the first stage of build the remainder being the fitting out. First the gunwales and the rubbing band are screwed and fixed, then the risers are put in to support the thwarts and the beam cut and shaped to support the stern thwart. The thwarts themselves are then cut and fitted, the whole being assembled to ensure a good fit. Everything is then disassembled and given four coats of varnish separately including the floor boards. The hull is also finally varnished and when all the components are dry the boat is put together for the last time. Varnishing takes a long time since each coat has to allowed to harden so that it can be rubbed down with progressively finer grades of sandpaper to ensure a brilliant and long lasting finish. Finally the spars, mast, gaff and boom are planed up from solid Colombian pine, sanded and varnished. The gunmetal fittings are now screwed to the hull and spars. The sailmaker delivers the sails and the boat is rigged with all its sheets, shrouds and blocks and we satisfy ourselves that the final result is fit to go to our customer. As you can see from the above a great deal of painstaking work goes into the building of one of our dinghies. Sadly the skills which go into producing them are getting rarer and it gives me some pleasure to know that my partners both in their early twenties will be around for a long time to practice them.