Deadrise - Measuring a Vessel's Hull

Boat on the water at sunset
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Definition

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 bulkhead.

Alternate Spellings

Dead Rise

Common Misspellings

Dead Rise

One way to make a quick assessment about the purpose and ride quality of a vessel is to view the stern from the rear so you can see the transition from chine to keel.

If it's a sharp V shape below the water means the ride will be smooth but the ship may wallow back and forth ferries and river boats have this design so they can operate in both directions without turning around.

 If the deadrise is shallow or flat at the stern the vessel will not have much roll or wallow but it will slap into the surface with each wave. A V shape allows a smooth transition while a shallower deadrise causes a sudden impact with each wave. The flat design has less drag and therefore is found on cargo ships and other low drag vessels. Cushion effect can be a problem for some heavily loaded cargo ships in shallow waters like canals.

A rolled, or soft, chine means the vessel is meant to lean and roll smoothly. This is true of most sail powered vessels where there is a counterweight in a deep keel.

Take a look at all kinds of common hull shapes to understand more about their uses. The definition of draft will also be useful when learning about naval architecture.

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Bruno, Paul. "Deadrise - Measuring a Vessel's Hull." ThoughtCo, Jul. 15, 2016, thoughtco.com/deadrise-measuring-a-vessels-hull-2292970. Bruno, Paul. (2016, July 15). Deadrise - Measuring a Vessel's Hull. Retrieved from https://www.thoughtco.com/deadrise-measuring-a-vessels-hull-2292970 Bruno, Paul. "Deadrise - Measuring a Vessel's Hull." ThoughtCo. https://www.thoughtco.com/deadrise-measuring-a-vessels-hull-2292970 (accessed May 22, 2018).