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Re: Seeking: Deadrise? For boats in general
By:John B.
Date: 3/5/2003, 11:04 pm
In Response To: Seeking: Deadrise? (Terry Hanson)

:Not In regards to the Cormmarant 16, but interesting anyway....

Bow deadrise
Deadrise is the angle of the boat's bottom to the horizontal. It is measured at both the bow and the transom. The relatively high bow deadrise seen here gives the boat a softer ride in a seaway. Knowing a boat's bow deadrise gives a feel for its seakeeping abilities. For example, a boat with a generous deadrise angle at the bow, maybe 60 degrees, will cut deeply into a sea as the bow drives downward. Imagine a knife cutting through butter. The sharp edge goes through easily, but the wide, flat side mashes the butter. A compromise is a wedge shape where the wider the wedge gets the less the knife penetrates. A boat's bow is similar to the wedge shape, which stops it from going too deeply into the water. When a boat has to drive into large waves, bow immersion is resisted by a large, flat chine (as shown here) and flared bow sections above the chine (as seen on a Carolina-style hull). A boat with low deadrise at the bow will plow through waves and slam.

Stern deadrise
Deadrise varies over the length of the hull. However, it is generally accepted that if the deadrise remains fairly constant from station six to the transom, as shown here, lift is appreciably greater and drag is reduced. The transom deadrise of this boat is 14 degrees. Deadrise gives the boat directional stability and reduces wetted surface as the boat rises onto a plane.

In rough terms, boats with:
transom deadrise angles of 0 to 5 degrees are better in flat waters
transom deadrise angles of 5 to 10 degrees generally stay close to shore
transom deadrise angles 10 to 19 degrees combine good seakeeping, fuel efficiency and speed in waves (think sportfishing boats)
transom deadrise angles greater than 19 degrees tend to be high-speed deep-vee craft
In general a lower transom deadrise angle results in a boat that is easier to get on plane and is very stable when stopped. However, it will have poorer seakeeping abilities when powering into a seaway. Boats with deadrise angles greater than 20 degrees generally perform best in a seaway, but they also tend to roll when stopped.

Messages In This Thread

Seeking: Deadrise?
Terry Hanson -- 3/5/2003, 10:55 am
Re: Seeking: Deadrise? For boats in general
John B. -- 3/5/2003, 11:04 pm
Re: Seeking: Deadrise?
Mark Woodhead -- 3/5/2003, 9:10 pm
Re: Seeking: Deadrise?
Kurt Loup, Baton Rouge -- 3/5/2003, 1:50 pm
Re: Seeking: Deadrise?
Tom Yost -- 3/5/2003, 11:18 am