Deadrise

Deadrise is the angle between the bottom of a hull and the horizontal, measured in a cross-section.

Always name the station

Deadrise usually changes along the hull, steepest toward the bow; a hull called constant deadrise keeps one angle over its after part. Variable deadrise names a bottom that is sharp at the bow and flattens toward the transom; one boating magazine calls that shape a warped plane. The atlas above shows how much the angle changes from one station to the next. The ITTC dictionary lists deadrise at midship and deadrise at the transom as separate quantities. When a spec sheet prints a single figure, boating writers say it is typically the transom angle. The atlas gives both stations for every hull, so a transom figure never gets read as the angle along the whole bottom.

The range

Industry guides and boating writers typically describe deadrise as zero or close to it on a flat bottom and as much as about 25 degrees at the transom of a deep V. A naval architect writing for BoatUS puts a deep-vee at more than 20 degrees, with a modified-vee between that and flat. The four hulls in the atlas step through that range at the same scale, so you can see what 0, 9, 15 and 22 degrees look like at the transom.

The trade-off, as sources describe it

Boating-course guides say a deep-vee hull tends to ride more smoothly than a flat bottom in rough water, and takes more power to move at the same speed. A flat bottom tends to use its whole surface for lift, with no shape left to soften slamming. The same BoatUS writer adds that a deep-vee tends to be most comfortable in a seaway and least comfortable lying at the fuel dock.

Those are tendencies of whole hulls at speed. Weight, speed, length, loading and the sea all change how a boat rides.

The other deadrise

On the Chesapeake Bay, a deadrise is also a V-bottomed workboat used by watermen, and Virginia law names it the official state boat. Everything else on this page is about the angle.