Quote:
|
Originally Posted by Bajan
Forgive my ignorance, but what is deadrise?
|
Since none of the 'experts' know what deadrise is I will enlighten the forum:
Bow deadrise
Deadrise is the angle of the boat's bottom to the horizontal. It is measured at both the bow and the transom. 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, lift is appreciably greater and drag is reduced. If 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.
In conclusion then, deadrise is the angle of a boat's bottom relative to the horizontal, and is measured at the boat's transom to determine the "V" of the boat. Modern "Deep V" boats have more than 20 degrees of deadrise, "Modified V's" have more than 15 degrees of deadrise, and "Semi V's" have 12 or more. It gets confusing because as new designs come out with deeper hulls, the definition shift. Some years ago 18 degrees was considered a real deep V. Now 24 or 25 degrees is a real deep V and 18 degrees is a modified V. A deeper V takes more power to get on plane, and usually pounds less in rough seas at speed. A deeper V is often less stable at rest, like when drifting, and has different handling characteristics at all speeds than a shallower V hull of the same length.
Hopefully the forum 'experts' will add and elaborate on my comments
u R right is from a book but are my comments cause I wrote them 
