Camber and other curves, How do we draw them?
Camber and other curves, how do we draw them?
In most of our drawings, we refer to "camber". This means a
curve going through three points, an arc of a circle. It is a very
simple curve that can be drawn with a batten or PVC pipe.
(Picture courtesy of Justin Pipkorn)
Camber is used in different places: for the molds (= stations = frames = bulkheads) or for other parts of the boat like the sole (cockpit floor) or seat tops.
Let's look at some examples:
In this drawing of a floor frame, we show that the bottom side has camber: 1-1/8" ( 28 mm).
To draw that curve:
- First draw the part with straight lines
-Mark the middle of the bottom side.
- Mark a point 1-1/8" offset from the middle.
- Draw a curve between the three points: the two end points and the offset middle point.
- That's all there is to it!
This is a seat top panel for a bow rider. All sides are straight except for the one along the hull: it has camber. The procedure is the same than for the floor frame above:
- Draw the complete outline with straight lines.
- Along the hull side edge, mark the middle.
- Offset that point 5".
- Draw a curve between the three points.
Next, the deck camber.
In the case of a station, we may not show the two sides of a part. This is customary in boat design: boats are supposed to be symmetrical, why complicate the drawing with unnecessary lines? The drawing shows a typical forward frame of a power boat with a small deck. All dimensions not relevant to this discussion were removed for clarity. Note that all dimensions are always taken from the baseline and the centerline.
Draw the outline for the frame, two sides, without the deck.
Mark the height of the center, draw the curve of the deck.
Last example, a transom with motorwell.
Draw the outline without deck.
Ddraw the deck curve.
Draw the motorwell cut.
Taking it one step at a time makes it simple.
Unless marked otherwise, camber is always measured from the middle of a line.
Cambered curves may be an approximation of the exact shape but the curves are always within 1/8" of the true curves.
We try to restrict our hull lines to second or third degree polynomials and this produces very fair cross section curves: conicals or plain arcs.