Deadrise is measured two ways, by linear measurement like inches or centimeters and by expressing it as an angle.
Let’s look at the angular measurement first. Looking at the cross section of a hull, draw a vertical line through the center of the vessel to the bottom of the keel. The top of this vertical line should be even with the chine, which is where the hull meets the topsides.
Now draw a horizontal line which intersects both sides of the chine and the top of the vertical line you drew before.
You should now have a 90 degree angle formed by the vertical and horizontal lines. Draw one more line from the point where your horizontal line meets the chine to the bottom of your vertical line at the bottom center of the keel.
The triangle you formed is made up of three angles. Deadrise expressed as an angle is the measurement in degrees of the bottom of the triangle.
To calculate deadrise in linear terms you will use the same triangle as above but now you will be using a ratio to express the deadrise. Much like the roof of a building, deadrise in linear terms is written as inches per foot.
First determine the number of inches from the 90 degree angle of the triangle along the horizontal leg to the chine. Next determine the measurement in feet from the bottom of the keel to the 90 degree angle of the triangle. Take the results and write then as inches/foot.
Deadrise is only a measurement at a single point on a vessel’s hull. Construction plans will note the deadrise at regular intervals along the length of the hull.
Since deadrise is a measurement based on the position of the chine it is possible to have complex expressions of deadrise because of multi-chine and planning hulls.
If you are asked to measure deadrise you should be given a point to make your measurement. For example; deadrise at 20 feet from bow, or deadrise at rear buklhead.