To find the number of planks required to form a float, to support a given weight.
1st. Find the content of one plank (vide [Practical Geometry], Part 12), and multiply it by the specific gravity of the wood; the product will be the weight of the timber.
2nd. Multiply the same solid content by the specific gravity of water: the product will be the weight of an equal bulk of water.
Then take the difference of these two products, or weight, and it will be the weight one piece of timber will support without sinking. Hence by Proportion, the number required to support the given weight may be found.
To find the number of casks required to form a raft to support a given weight.
1st. Find the solid content of one cask in cubic inches (vide [Practical Geometry]), and multiply it by the specific gravity of water; the product will be the weight of a quantity of water of equal bulk with the cask.
2nd. From this product, or weight, subtract the weight of the cask, and the remainder will be the weight it will support without sinking. Then by Proportion, the number required for the formation of the raft may be found.
To find the number of boats, or pontoons, required to support a given weight.
The burthen a boat, or pontoon, will support without sinking beyond a given depth (the form of the boat, or pontoon being known) must first be found, thus—
1st. Find the solid content of the part to be sunk, in cubic feet (vide [Practical Geometry], Part 12), and multiply it by the specific gravity of water (vide [Gravity], Part 12).