Boating term of the day: what is Deadrise?

Thanks to Weldcraft and Tom George for this:

You may have heard the boating term Deadrise before but if somebody were to challenge you to fully explain it, could you? Well, now you can!

The deadrise of a boat is the angle measurement between the boat bottom and a horizontal plane on either side of the center keel.

The deadrise of a flat bottom boat is much lower (or zero) compared to a vessel with a deep-V hull.

It is also sometimes defined as the angle of the V on a hull, and is measured from one half of the hull’s rise from keel to chine against the horizontal. (19 degrees deadrise= 19 degree angle up from horizontal).

When someone mentions a boat’s deadrise, they’re usually talking about the angle at the transom, though deadrise can refer to the angle at any point along the hull. Most folks refer to the deadrise at the bow as the “entry“.

The amount of deadrise is an important metric because it gives the boat owner an idea of how well the boat will run or cut through rougher seas.

A larger deadrise value will cut through seas easier and generally provide a softer ride.

Understanding how a hull’s shape is constructed is a critical factor in selecting the boat that will best fit your needs. A key factor to understand is deadrise.

Deadrise is a measurement of the degree of angle between two surfaces. A boat’s deadrise is the amount of angle that forms between the boat bottom and a horizontal plane on either side of center keel.

The deadrise angle is the least (meaning flattest) at the transom and gradually increases (more vee) as the bottom goes forward and then increases at a greater rate at the bow.

Most manufacturers list only a single deadrise measurement. This can be very misleading as the exact point at which the measurement is taken can vary dramatically from model to model.

The transom deadrise is the most commonly cited deadrise value, however, because most boats run on the aft 30-50% portion of the hull.

Occasionally, a manufacturer will only provide the highest (steepest) deadrise measurement, which most often occurs at the furthest point forward on the bow.

This measurement point is misleading as it is above the waterline and would only have an effect on performance in extreme conditions.

Is there a downside to a large deadrise value? The tradeoff of cutting through chop with ease while running the boat typically comes when the boat is going slow or is at rest.

While the deeper-V hulls can cut better through water, a flatter bottom boat will be more stable at slow speeds or when not moving. 

Many manufacturers attempt to find a happy medium where the boat will carve nicely through rougher seas but also maintain good stability while at rest or when trolling.

It’s worth noting that deadrise isn’t the only factor in stability and a soft ride. Beam width can also have an effect on both ride and stability. A wider boat, generally, will begin to “pound” on the water sooner than a more narrow boat with the same deadrise. Similarly, a wider beam boat will typically have more stability at rest.

As multiple characteristics of the boat can affect ride comfort and performance, the importance of sea trials is always worth mentioning. Getting out in the open water with a boat is the best way to compare how vessels in various conditions. Experienced boaters know that while specifications on each boat are important, assumptions based on such numbers can be mistaken once the boater gets a feel for the boat out on the water.

Weldcraft Deadrises