What Are Offsets on a Kayak?

Offsets are groups of numbers that describe the shape of a kayak. Because the data is difficult to process in its basic form, offsets are usually put into tables to help understand the design of the kayak more easily. From the table, a simple drawing can be created in the form of a graph to show the actual shape and dimensions of the kayak.

  1. Offset Table Axes

    • The height and half-breadth tables perform the same function, providing an x coordinate for a given y coordinate. The offset number format is like this: 1-10-2+. The first number is the distance in feet from the baseline. The second number is distance in inches from the baseline. The third number is distance in eighth-inches from the baseline. For example, according to Bear Mountain Boats, 1-03-7+ equals one foot, three inches, seven-eighths and a sixteenth, giving a total of 15 and 15/16 inches. Height gives the altitude off the strong-back at any given buttocks -- the vertical slices parallel to the center line -- and half-breadths indicate the distance from the center point at any chosen waterline.

    Plotting From Offsets

    • Lay out a grid with waterlines spaced every 2 inches for the half-breadths. Add buttock lines spaced at 2-inch intervals for the heights, and use the same center line and baseline to join the two portions of the graph together. Waterlines can be incremental, increasing by 2 inches each time to give 2-inch, 4-inch, 6-inch, 8-inch, 10-inch, 12-inch and 14-inch separations. The table heights are then plotted on the buttock lines and are measured downward from the baseline to create a pattern of dots or small crosses which can then be joined into a smooth line. The same baselines are used for both hull and deck offsets.

    Shape of Curve

    • According to Bear Mountain Boats, a fair curve should pass within 1/32-inch of each plotted point, and this gives an allowance in measurement for the 1/4-inch strips. The final drawn station is the true shape required for cutting of the station mold and should give a smooth result in practice. Stem mold offsets are measured forward from a predetermined station and are to the front edge of the inside stem. The ideal thickness of the inside stem for kayaks is given as 1 inch, so the ideal line must be drawn back from the plotted line to produce a true stem shape, which can then be transferred from the plan to the physical object.

    Half-Forms and Symmetry

    • The half-form of a kayak drawing shows the center point, about which the two halves of the built boat will have symmetry. One half-form mirrors the other half-form, and makes kayak building more straightforward than a boat with unequal halves. When drawing out the shape of a kayak using the offsets, it is important to keep the lines of the graph gently curving and symmetrical. Sometimes, a successful plan is created by plotting only on the right or left half of the graph first, then reproducing the mirror image later. This helps when the plan is transferred to board. High levels of symmetry can help when dealing with the forces involved in using a kayak, as described by the San Onofre Paddle Surfing Association.