A Guide to Motor Boat Design and Construction - A Collection of Historical Articles Containing Information on the Methods and Equipment of the Boat Builder. Various

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      CONSTRUCTION OF THE HULL

      BOATS, MOTORS, AND CRUISING HINTS

      CONSTRUCTION OF THE HULL

      THE construction and design of the hull will very much depend upon the type of service to which the boat will be put.

      A boat intended for river use, for instance, would be of much lighter construction than a boat which had to contend with heavy weather at sea.

      The boats usually offered to the public and built by our leading boat builders are the result of considerable research on the part of naval architects, who have been up against many difficulties.

      It will be seen that to design a craft for either river or sea work would present little difficulty to those experienced in the work, but to design a craft that will be clean running, giving an absence of wash, for river use, and at the same time be safe and reliable at sea, is no simple undertaking.

      This problem has been tackled and overcome by designers, and the pleasure craft offered to the public to-day are not only clean running and economical, but can be safely taken to sea in even very bad weather.

      So much headway has been made and the confidence of the public gained that motor boating no longer exists in the category of rash and dangerous pastimes.

      Generally speaking, the class of boat in which the reader is likely to be interested is made of wood, although there are manufacturers specialising in the construction of hulls in metal. We shall, however, confine our attentions to the wooden variety, and see how they are constructed.

      It will be assumed that the reader desires to purchase a boat and not to attempt to build one, any more than he would contemplate building his own car.

      A knowledge of how the hull is built, and the materials of which it is composed, will interest him, and enable him to converse intelligently with the boat builder when selecting a craft to suit his requirements, or in discussing repairs and overhauls in the case of second-hand craft.

      The methods of building wooden craft are divided into two classes, known as Carvel and Clench or Clincher building.

      Carvel building is generally resorted to in the larger and more expensive class of boat, whilst clincher-built craft seldom exceed 30 ft.; dinghies, small rowing boats, and fishing craft are usually built in this manner.

      In the carvel method the planks which run from fore to aft are fitted edge to edge on the butt principle, and the seams caulked with cotton to make them watertight.

      This method results in a smooth and clean-running hull, but is, of course, the more costly.

      Carvel-built hulls may be of the single- or double-skin type. In this case the planking does not run fore to aft as in the single-skin method, but two skins are laid and run diagonally, but in opposite directions; between them a canvas lining is fitted to render the skin watertight.

      At this point it would be as well to point out that a boat’s lining must not be mistaken for a second skin. Linings are often put in a boat to neaten up the interior appearance and cover up the somewhat unsightly timbers.

      Skins in the true sense of the word are never put on the inside of the framework, but always on the outside.

      The planks are riveted with copper rivets to the frame members, which are known as timbers, but in the case of double planking they are often sewn with copper wire.

      The timbers which constitute the framework are bent to the cross-sectional design of the boat, being fastened in the centre to the keel, while the two upper extremities of the thus formed terminate in the gunwale, which is the upper edge, and consists generally of a moulding running right round.

      The planking is fixed at the fore end to the stem, a vertical piece of wood, usually a naturally grown oak crook, not unlike a hockey stick in shape. This is scarfed or jointed to the fore end of the keel.

      The planks are secured at the rear or aft end to the transom, which is really the back of the boat, and in all but the larger craft is made in one piece and fixed to the after end of the keel.

      The shape is preserved in the case of open craft by the seats, known as thwarts, which are fitted across the boat.

      In the case of cabin boats the shape is preserved by the bulkheads or partitions between the cabins, and also the deck beams.

      Fig. 1 shows a typical small open launch, and the construction is clearly shown, the vertical lines representing the timbers.

       FIG. 1.—SECTION AND PLAN OF SMALL OPEN LAUNCH.

      In Fig. 2 we have a sketch to demonstrate the lines of a boat.

      The top sketch shows it in profile, whilst the centre and lower sketches represent the cross section and plan views. By following down any of the vertical lines, A, B, C, D, E, F, G, the shape at any point can be found for the width.

      The reader would be well advised to ponder over this diagram for a few moments to make himself familiar with the various shapes of the hull at various points in its length.

      The width of a boat is known as the beam, whilst the underwater part is known as the draught, and that part above water is termed the freeboard.

       FIG. 2.—LINES OF BOAT.

       FIG. 3.—DETAIL OF CARVEL CONSTRUCTION.

      Figs. 3 and 4 show the two methods of carvel planking, namely, the single- and double-skin methods.

      It should here be pointed out that in the doubles-kin type vertical ribs are usually dispensed with, and horizontal rails called “stringers” are substituted.

       FIG. 4.—DETAIL OF MULTIPLE-SKIN CONSTRUCTION.

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