Читать книгу 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 - Страница 8

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.

The clincher or clench method of planking differs from the carvel system in that the planks are not butted, but overlap. The rivets are driven through the place where the two planks overlap; in all other respects the construction of the hull is the same as for carvel building. Fig. 5 illustrates this method.

FIG. 5.—DETAIL OF CLINCHER CONSTRUCTION.

Fig. 5 shows the clincher system of construction, in which will be noted the simple form of joint of planking.

The materials favoured for the construction of the various parts of the hull are: timbers, elm; keel, elm; stem, naturally grown oak crook; transom, oak or teak. Planking is usually carried out in mahogany, teak, or pine. All rivets used are copper.

The finish imparted to the hull depends very much on the material used and the size of the boat.

It is usual in craft up to 25 ft. in length to varnish above the waterline, whilst that portion below the water is usually painted with a special anti-fouling composition, which retards the depositing of barnacles and sludge on the bottom of the boat. This antifouling paint is usually manufactured in black, red, and green.

Larger craft and cabin boats are generally painted all over, the interior fittings, seats, etc., only being varnished.

The steering of small boats where the engine is fitted fairly well aft is accomplished by means of the ordinary tiller, but in larger craft where the helmsman could not get at the engine controls the steering is done by wheel.

The arrangement is quite simple. A wheel, to which a drum is fixed, has a steel rope wound once or twice round it, and a screw is fitted through the centre turn to fix it. The two ends are then led through a series of pulleys to the tiller. Fig. 6 should make this point clear. Turning the wheel either way shortens the steel rope on one side and pays out on the other, so pulling the tiller over.

So far we have only considered open boats, but the reader will be well advised to spend a little more money and invest in a cabin boat, known as a Cabin Cruiser.

The essential points of hull construction are adhered to, but in order to get a cabin on, say, a 25 to 30-ft. boat means that it must be built up, for there would not be sufficient depth in a craft of this length to form a cabin by merely decking a portion over.

FIG. 6.—LAYOUT OF STEERING ARRANGEMENTS.

In order to form the cabin the sides of the boat are built up for about two-thirds of the length (from bow to stern).

The height to which this can be carried will be determined by the stability of the craft in question.

In craft of considerable beam this can be done successfully, but with those of small beam more care has to be taken or the boat will be top-heavy.

The cabin work can be higher in river craft than on boats intended for use at sea, where the height of the cabin has a tendency to cause the boat to roll. With a stiff wind blowing broadside on, considerable drift or “leeway” is made, and constant correction of the course becomes necessary.

FIG. 7.—CABIN LAYOUT OF TYPICAL 30-FT. CBUISER.

As a rough guide it may be stated that a 30-ft. boat is the smallest size in which it is possible to obtain full headroom inside the cabin.

The actual layout and design of a cruiser depends upon the owner’s requirements. If the boat is intended for daytime cruising only, then one large cabin may suffice, but in the case where it is proposed to live on board additional accommodation must be provided. Fig. 7 is the layout of a typical 30-ft. cabin cruiser, suitable for week-end cruising.

A more luxurious type, however, is what is known as the bridge deck cruiser, illustrated by Fig. 8.

In this type, there is a saloon forward, then the bridge deck, aft of which is a sleeping cabin. The engine in this case is under the floor of the bridge deck.

A great feature about this type of craft is the complete protection from the weather.

The bridge deck may be provided with side curtains, thus making it into an additional cabin if required.

Fittings in the form of mooring cleats, rowlocks in small craft, and rudder bearings are usually made in bronze, gun-metal, or brass, although galvanised iron is used in cheaper quality work.

FIG. 8.—A BRIDGE DECK CRUISER.

On no account, however, must dissimilar metals be used in conjunction with each other, that is to say, a brass fitting must not be secured with iron screws, or the combination will be eaten away by galvanic action directly they become saturated with salt water. What actually happens is that the two metals form the elements of an electric battery, and the salt water the solution or electrolyte.