Boat House and Workshop
"A Good Coat of Paint on the Shingles Will Lengthen the Life of the Roof Fully Five Years."
The next thing was to take down the heavy timbers of the barn, still standing. Fred saw at once that they were too heavy to be removed without mechanical aid or more human help, so he brought from his father's stable a rope and set of pulley-blocks like the ones shown in [Fig. 11]. Nick, who had seen some service at sea, hooked the block into a loop formed by a short piece of rope tied over a limb projecting from one of the trees. The question of lifting the timber now was an easy one, as another short rope was tied to the heavy post W, in this case the weight P being the power. Each of the blocks shown contains pulleys which make the relation of the weight to the power as one to four. The weight being sustained by six cords, each bears a sixth and a weight of six pounds will be kept in equilibrium by a power of one pound. The blocks used in a system of this character are called single if there is one pulley in each, double if there are two, treble if there are three, and quadruple if there are four.
Fred, George, Nick, and Jessie who liked to help whenever she could, counted for four times their number when they all pulled together on the rope P. It was astonishing to the youngsters how easily the heavy timbers were taken down and piled in a nice heap.
Two timbers, each about twenty-five feet long, were chosen and marked, to be used for slides or ways, on which the proposed boat could be hauled in and out of the boat house. It was quite a distance from the timber to the river end of the boat house, and, the former being heavy, Fred decided to make an inclined plane of planks—of which there was an abundance—so that the timbers could be slid or rolled down to the river. It took but a few minutes to lay the planks, and as the incline was gentle, rollers were used and the timbers went down as easily as the big rock had done. This pleased the younger children very much.
"When papa comes home," said Jessie, "I'm going to get him to tell me about the 'inclined plane' as well as the ropes and pulleys."
The two timbers were rolled into the river and floated to the boat house, where one end of each was raised to the floor level at the doorway and made fast; the other end sank to the bottom, where Nick dug down and made a bed for it to rest in. These beds were made deep enough to bury the ends, and large stones were then thrown in to keep them from moving, but these were not allowed to reach within 18 inches of the surface of the water, which was then at its lowest mark. The timbers were kept about three feet apart, ample space to admit of any ordinary launch or row boat being taken into the boat house.
"Oh, Fred," said Jessie, "do you think those two sticks will be strong enough to hold the boat while you are pulling it up?" "Why, yes; strong enough to hold a dozen boats no larger than the one we intend having made. I don't know how much weight these timbers will support, nor how heavy our boat will be with the engine in it, but I'm sure the timbers are strong enough."
Jessie's question, however, caused Fred to think over the matter, and he set to work to find out how to tell the strength of timber beams. He discovered that to be able to determine the strength of beams and wooden pillars under all sorts of conditions required considerable training in mechanics and mathematics, but that the case before him was comparatively easy. A general rule for finding the safe carrying capacity of wooden beams of any dimensions, for uniformly distributed loads, is to multiply the area of section in square inches, by the depth in inches, and divide their product by the length of the beam in feet. If the beam is of hemlock, this result is to be multiplied by seventy, ninety for spruce and white pine, one hundred and twenty for oak, and one hundred and forty for yellow pine. The product will be the number of pounds each beam will support. For short-span beams, the load may be increased considerably. Fred, who had some knowledge on the subject, acquired at the training school, determined to pursue his studies in this direction.
In talking over the matter of nails with his father, their holding power was mentioned, and Mr. Gregg told Fred of a test that had been made some time ago by the U. S. Ordnance Department, where cut and wire nails had been tested respectively, showing a decided superiority for the former, both in spruce, pine, and hemlock. Thus in spruce stock nine series of tests were made, comprising nine sizes of common nails, longest 6 inches, shortest 13⁄8 inches; the cut nails showed an average superiority of 47.51 per cent.; in the same wood six series of tests, comprising six sizes of light common nails, the longest 6 inches and the shortest 11⁄8 inches, showed an average superiority for cut nails of 47.40 per cent.; in 15 series of tests, comprising 15 sizes of finishing nails, longest 4 inches and shortest 11⁄8 inches, a superiority of 72.22 per cent. average was exhibited by the cut nails; in another six series of tests, comprising six sizes of box nails, longest 4 inches and shortest 11⁄4 inches, the cut nails showed an average superiority of 50.88 per cent.; in four series of tests, comprising four sizes of floor nails, longest 4 inches and shortest 2, an average superiority of 80.03 per cent. was shown by the cut nails. In the 40 series of tests, comprising 40 sizes of nails, longest 6 inches and shortest 11⁄8 inches the cut nails showed an average superiority of 60.50.