Depth in the Hold to Displacement

The height between the floor and the lower deck. This is one of the principal dimensions given for the construction of a ship. It varies according to the height at which the guns are required to be carried from the water, or according to the trade for which a vessel is designed.

The art of designing as distinguished from making a block model by the eye and building a boat from it first attracted public attention about twenty years ago. At this time the iron cutter yacht Vindex was brought out. The Vindex was designed on a drawing board and the lines made to the outside of the plank, while the displacement, centre of gravity of the same, centre of lateral resistance and various other elements were calculated before the model was made, and when these matters were settled the model was made, but the boat was built from the lines as drawn. Shortly after this other boats were built after the new method, and though the battle was fought by the model makers with great vigor, the new method has conquered and now naval architecture is a fashionable profession. The drawing board method is to assume a load water line, and all other dimensions are proportionate to this dimension. The plan is drawn to the outside of plank, and the model, when made from the lines, is exactly like the proposed boat. The displacement centre of gravity of the same, centre of lateral resistance, area of cross sections and other elements are all predetermined points. This seems to be but common sense, but the block model system was so strongly intrenched in the affections of yachts-men that no amount of ridicule was enough to heap on the heads of the "paper boat builders."

A line cutting the body-plan diagonally from the timbers to the middle line. It is square with, or perpendicular to, the shape of the timbers, or nearly so, till it meets the middle line.

A narrow plank, made to a line formed on the half-breadth plan, by taking the intersections of the diagonal line with the timbers in the body-plan to where it cuts the middle line in its direction, and applying it to their respective stations on the half-breadth-plan, which forms a curve to which the ribband is made as far as the cant-body extends, and the square frame adjoining.

The weight of water displaced by the bottom and the sides of a vessel below the water line. The displacement is a predetermined quantity and time and care are taken to figure it correctly.

One way is to set off at the station of cross section the area in linear feet, on a small scale for convenience; then make a curve of versed sines for the forward body. The after body being a trochoidal curve, based upon a radius of one-tenth of the length of the after body. A curve is drawn to take in these points and the L W L divided up by ordinates and a calculation made of the contents. As the linear feet at cross section represents the area of that section, so does every point in the curve represent the area of a section at that point, and the result of the calculation is the half displacement. It has been found that the displacement, as shown on this curve, comes very close to that of the best boats and may be accepted as a law.

This method was outlined by Mr. John Hyslop, of New York, about the time that it was presented to the public by Mr. Colin Archer, of Norway, and we are indebted to the labors of these gentlemen for a displacement shown on one line.

The theory is that the line of least resistance is a curve of versed sines for the fore body and a trochoidal curve for the after body, and this idea is applied to the cross sections and not to the water lines. For, though there have been large vessels that had a true versed since curve below the water line no rule could be given as to how much or how little should be taken off the fine end of the curve for a water line for a small boat, and moreover this line could only be applied to a boat of great beam and shallow body, and this type of model is a poor sea boat and unsafe.

If the displacement should be too small a larger cross section must be made and the curve projected anew and a new calculation made. The draught of water power to carry sail and general behavior of the boat depends upon the displacement.