Boys' Book of Model Boats Part 11

CHAPTER XIV

TWO-FOOT SAILING YACHT

THE model yacht described in this Chapter is the design of Mr. W. J.

Daniels, of England, and was described by him in "Junior Mechanics." Mr.

Daniels is one of the best known and most successful English designers of model yachts, and the one here described can easily be constructed by the average boy:

In order that the reader may realize the obstacles to be surmounted in designing a model yacht that will sail in a straight line to windward, irrespective of the different pressure that the wind may expend on the sails, it must be pointed out that the boat is continuously altering the shape of the submerged part of her hull: therefore, unless the hull is so designed that harmony is retained at every angle to which the pressure of wind on the sails may heel it, the model's path through the water will be, more or less, an arc of a circle. Whether the boat sails toward the wind, or, in other words, in a curve the center of the circle of which is on the same side of the boat as the wind, or in a curve the center of the circle of which is on the opposite or leeward side, will depend upon the formation of the boat.

As these notes are intended to first initiate the reader into the subject of model yacht building and construction, the design supplied is one in which all things, as far as shape is concerned, have been considered.

It is the endeavor of every designer to produce the most powerful boat possible for a given length--that is, one that can hold her sail up in resistance to the wind-pressure best. Of course, the reader will easily realize that breadth and weight of keel will be the main features that will enable the model to achieve this object; but, as these two factors are those that tend to make a design less slender, if pushed to extremes, the designer has to compromise at a point when the excess of beam and buoyancy are detrimental to the speed lines of the hull.

But the question of design pure and simple is a complex one, and we do not intend to weary the reader just now with anything of that kind, so we will now proceed to build the hull. In order that we may correctly interpret the shape shown in the design without being expert woodcarvers, we must use our ingenuity and by mechanical means achieve our object, at the same time saving ourselves a large amount of labor, such as we should have to expend if we made this boat from a solid block of wood.

Now, as regards understanding the drawings: it is essential to remember that a line which in one view is a curve is always a straight line in the other two views. Those lines which are drawn parallel to the water-line are known as water-lines, and it will be seen that the curves shown on the deck plan represent the actual shapes of the hull at the corresponding water-lines above, below, and exactly on the load water-line.

In other words, if after the hull is made it were sunk down to these various levels, the shapes of the hole made in the surface of the water would be as shown in the plan.

Therefore, instead of making our boat from a solid block of wood, we will make our block up from several layers, the thickness of each layer being equal to the s.p.a.ce between the water-lines; but before gluing these layers together we will cut them out to the exact shape that the boat will be at their various positions.

It will not be necessary to have a separate piece of wood for each layer, as some layers below the actual water-line will be cut from the pieces of wood that have been cut out from the layers above.

In this case, the boat being 24 inches long, the top layer will be the same length and breadth as the boat, and 1 inch in thickness.

Draw down the center of the board a straight line, and other lines square to it, representing the position of the cross-sections as shown in the drawing. You have now to transfer the deck line to this board, and this is done by marking the breadth at the various sections and drawing a curve through the spots, a thin strip of straight-grained wood being used as a rule, the latter being held down by such weights as are available. For the purpose of laying off the water-lines truly, lines s.p.a.ced at 1-1/2 inches are shown; the first, it will be noticed, is half a section or 3/4 inch from the stem head.

The material required will be a board of pine about 6 feet long, 8 inches wide, and 1 inch finished thickness.

Nearly all wood-yards stock first-quality pine, but it is in planks 3 inches thick. You can no doubt pick up a short length about 4 feet long.

If so, take it to a sawmill and have two boards 1-1/4 inches thick cut and then machine-planed down to a dead inch. Perhaps you can purchase a board that is already cut, and is fully 1 inch thick, to allow for planing.

Prepare one edge of the board straight with a plane, seeing that it is square to the surface.

As a planing-machine always leaves a series of ridges across the board, varying according to the quality of the machine, it is necessary before transferring the lines to the wood to just skim the surface with a nicely sharpened plane, and set so as to just skim the wood.

[Ill.u.s.tration: FIG. 153]

The lengths required are: _A_, plank 24 inches long; _B_, plank 24 inches; _C_, plank 18-1/2 inches.

The _D_ plank will be cut from the center of _B_, but will have to be shifted two sections forward.

Having transferred the various shapes from the drawing on to their respective layers, you saw out each carefully with a bow or a keyhole-saw, care being taken not to cut inside the lines. It is better to cut full, and trim down to the lines with a chisel or plane. A good deal of trouble can be saved by the expenditure of a few cents for having them machine-sawed, in which case ask the sawyer to use his finest-toothed saw.

Having cut out layers _A_, _B_, _C_, and _D_, fresh lines are marked, as shown by the dotted lines in the plan. These indicate the shape of the inside of each layer when the boat is carved out, and save labor.

These may as well be sawed out now as carved out later. It will also facilitate gluing up, as it will allow the superfluous glue to be squeezed out, and also decrease the breadth of the joint.

In order to get these various layers glued together dead true to their positions as indicated in the design, you must choose a section about amidships, say section 11, and with a square draw a line from that section, which is, of course, still showing on the surface of the layer, down the edge on either side, joining up with a line across the opposite face. Also vertical lines at each end of the midships line must be drawn on the wood, great care being taken to get the midships line on the under face of the layers dead opposite each other.

[Ill.u.s.tration: FIG. 154]

[Ill.u.s.tration: FIG. 155]

If your outfit contains half a dozen carpenter's hand screws, these can be used; but if not, it will be necessary to purchase from a hardware store eight seven-inch bolts and nuts 3/8 inch in diameter, with one washer for each, and to make up four clamps, as shown in Fig. 156.

[Ill.u.s.tration: FIG. 156]

You will start by gluing layer _C_ to layer _D_, blocks being placed between the surface of the layers and the clamps to prevent bruising the wood. These two are then glued to layer _B_, and when this is thoroughly set they are glued to the layer _A_. The best glue to use for this job is marine glue, which does not dry too quickly, and so gives plenty of time to see that the layers have not shifted. In every case one clamp should be placed at each extreme end of the shorter layer, so as to insure the ends making contact, the other two being placed equidistant.

While waiting for the glue to set, you can be preparing the four layers (shown below _D_) for the lead keel pattern. The lines must be cut out, in this case, with a chisel, as it will be noticed that the lower faces must be left wide enough to receive the top face of the layer beneath it.

It will be noticed that the under face of each of these layers extends beyond the top face aft, and allowance must be made for this. On laying off the lines on the fin layers, do not join up with a point each end, but leave about 1/8 inch thickness, as shown on the drawing.

These layers must be drilled through to take the keel-bolts, which are made from two motorcycle spokes, twelve-gage. These should be cut to a length of 5-1/2 or 6 inches. Great care should be taken to insure that the midship lines are exactly vertical over each other when these layers are glued up.

Before gluing these four layers on to the hull proper, they should be held in position by means of the spokes, in which position they can be sawed to shape for the keel pattern. First, with a small plane or sharp chisel cut down roughly, then a rasp and different grades of sandpaper are used, working across the joints.

It will be realized that, if the pattern for the keel were cut off dead on the line indicated on the design, there would be a loss of wood through the saw cut. In order to obviate this, another line 3/16 inch below the proper lead line is drawn, and the saw cut made between these two lines. You will now plane down each face that is left rough by the saw, straight and square to each of these lines. On the top face of the pattern for the lead, glue or tack a piece 3/16 inch thick along the face, and cut down the edges flush.

You will by this means have made up for the amount of wood carried away by the saw. You will no doubt find a difficulty in holding the pieces of wood for planing in the ordinary way, but it is simple enough if you set the plane nicely, grip it in a vise or bench screw upside down, and push the work over the plane's face, instead of vice versa. But be careful of your fingers!

Take the pieces left from the spokes when cutting down to length, and put these in the holes in the keel pattern. These are for cores, and if you take your pattern to a foundry they will cast it for a small amount, with the holes in it.

Shoot the top face of the lead in the manner before described, and fit on. The hull is now ready for carving out. Screw on your bench two pieces of wood about 18 inches in length and 4 inches wide, so that they project over the edge of the bench about 10 inches. These should be about 15 inches apart. Place your hull upside down on them, and fix it by nailing upward into the top layer. After cutting off the corners of the layers roughly with a chisel you use a small plane set fairly fine, and work all over the hull evenly, taking care not to cut below any of the joints. A small gouge will be required to clear the wood from the region of the after fin, a round rasp--sandpaper being wrapped around a small stick--being used for smoothing down afterward.

Templates of the cross-sections should now be made from thick white paper. This is done by p.r.i.c.king through the design to transfer their shape onto the paper. The cross-sections have on this account been produced here actual size. If cross-lines representing the water-lines are drawn, you will have an excellent guide for fitting, as these lines will, of course, come opposite each glued joint.

Try your templates now and again as you work, and do not try to finish one spot, but keep the whole at an even stage, and you will see the hull gradually grow into shape.

The topsides (which is the name given to that part of the vessel's hull above the water-line) are responsible for the boat's appearance when afloat, and until the top sheer is cut off the boat looks very disappointing. The cross-lines being still on the upper layer, draw square lines from them down the topsides and from the drawing mark the points through which the sheer-line runs. The thickness of the deck must be allowed for, and as this will be just over 1/16 inch, the line must be drawn this much below the finished sheer-line. The arch of the transom must be marked, and the hull cut down to the sheer. To avoid the risk of splitting, a number of fine saw cuts are made down each section line and two or three at the transom.

You now proceed to carve out the inside. Pad your bench bearers and rest your hull upon them. A curved wood gouge with a fairly flat edge is the best tool. Get it nicely sharpened, and work all over the inside of hull until it is about 3/16 inch thick, the top edge being left 3/8 inch wide.

Keep holding up to the light until it is showing a blood-red color, and smooth down the gouge marks with coa.r.s.e sandpaper.

The hole for the stern-tube must now be drilled, and the tube made and fitted. The hole should be 1/4 inch in diameter. First drill a smaller hole, and then with a 1/4-inch rat-tail file slowly open it out, at the same time rubbing a groove down the stern-post. The stern-tube is made from a piece of light-gage bra.s.s tube, it being cut away with a piercing saw to leave a strip the length of the stern-post. Drill three holes in the strip at equal distance and large enough to take a 1/4 inch bra.s.s screw, No. 0 size. Temporarily screw the tube in position, and from a piece of thin bra.s.s make a plate for the inside. An oval hole will have to be made in the plate to enable it to seat flat over the tube. Solder this while in position.

Then remove the whole, and replace, after white-leading where wood touches bra.s.s.

The deck-beams, three in number and 1/4 inch square in section, must now be fitted. The sheer edge which we left 3/8 inch wide must be recessed to receive the beams, the recess being made with a 1/4-inch chisel.

Before gluing beams in, three coats of good varnish must be applied to the inside of sh.e.l.l.

The deck should now be prepared and fitted. You will require a piece of pine of ample length and breadth, 1/8 inch in thickness, and after planing finely and sand-papering, pieces of the same stuff should be glued on the under face to reinforce it where the bowsprit, keel-plate, hatch rim, and mast will be fitted. Cut these pieces to shape before gluing on.

Before doing the latter, apply a coat of clear size to the upper face of the deck; this will bring up the grain, so paper it down when dry.