On 20 Jan 2006 20:23:12 -0800, "markvictor"
wrote:

Dan Krueger wrote:
markvictor wrote:
Gene Kearns wrote:

So, have a great day Skipper. I'll think about you as the waves lap
against my 20 degree deadrise transom on my "dilapidated, age stained
and grungy" boat.... and wonder if deadrise on a perpetually dry boat
matters at all!


Your "deadrise" is measured on the bottom of your hull...not the
transom...


Deadrise is the angle of the hull at the transom. You can't measure it
at the bottom of the hull.

Dan

Sorry Dan, I can't agree with you. Having installed 100+ transducers
on just about every type of hull imaginable, I can tell you without
reserve that you absolutely can measure deadrise angle on the bottom of
the boat, the DIY ers use a level and a framing protractor, or a
level,two straightedges, a calculator,and a little guidance by
Pythagorus...I , on the other hand, use an electronic inclinometer, it
takes all of 2 or 3 seconds...
This is to ensure that the sounder or FF is looking at the bottom under
the boat it is installed on, not 50 ft. to 1 side or the other. When
the deadrise spec. is given for a boat ,it is essentially telling you
how deeply a hull is "Vee'd" You can measure deadrise at the transom,
but this will not always give you the construction specification
deadrise value, rather it will give you the deadrise of the aftermost
portion of your bottom, but regardless, deadrise is your bottom's
angle, not your transom's angle. But you don't need to take my word
for it, here's what the ABYC standard says:

"Deadrise Angle" is the angle, taken at midship, at which the hull
slopes up from the horizontal (e.g., A flat bottom vessel has a
deadrise angle of zero degrees; a high deadrise angle value indicates
a deep V-hull);
Regards,
markv

"Midship"! That blows me out of the water. I'd always thought it was
measured at the transom too. Thanks for the enlightenment.
--
John H

******Have a spectacular day!******

"The first part of the answer in determining how deadrise affects
performance is another question: deadrise measured where? If the angle
between a horizontal plane tangent to the keel and the chine is
measured just aft of the bow, most modern boats will measure around
45° or more. If measured just forward of the stern, the deadrise may
be as little as 5°. The days when deep-V hulls carried the same high
angle of deadrise nearly constantly from bow to stern is long gone.
Why? Because they didn't perform very well."

Hey John, this is a pretty fair explanation of the reason for using a
measurement somewhat forward of the transom for a published spec...It's
not so much of an average angle, as it is the angle at the widest
"wetted" area of the hull at speed..the low deadrise at stern provides
stability, especially with engines mounted well aft.. a high angle
carried all the way aft tends to make a boat "porpoise" at speed...too
low an angle causes instability when turning at speet, too rapid a
transition and you get a boat that meanders at low speed, and can
develop low pressure areas at speed that can negate lift or planing
ability..

On 21 Jan 2006 09:31:38 -0800, "markvictor"
wrote:

"The first part of the answer in determining how deadrise affects
performance is another question: deadrise measured where? If the angle
between a horizontal plane tangent to the keel and the chine is
measured just aft of the bow, most modern boats will measure around
45° or more. If measured just forward of the stern, the deadrise may
be as little as 5°. The days when deep-V hulls carried the same high
angle of deadrise nearly constantly from bow to stern is long gone.
Why? Because they didn't perform very well."

Hey John, this is a pretty fair explanation of the reason for using a
measurement somewhat forward of the transom for a published spec...It's
not so much of an average angle, as it is the angle at the widest
"wetted" area of the hull at speed..the low deadrise at stern provides
stability, especially with engines mounted well aft.. a high angle
carried all the way aft tends to make a boat "porpoise" at speed...too
low an angle causes instability when turning at speet, too rapid a
transition and you get a boat that meanders at low speed, and can
develop low pressure areas at speed that can negate lift or planing
ability..

The definition you provided makes perfect sense! I've just always thought
incorrectly. Thanks for screwing my head on properly.
--
John H

******Have a spectacular day!******

JohnH wrote:
On 21 Jan 2006 09:31:38 -0800, "markvictor"
wrote:


"The first part of the answer in determining how deadrise affects
performance is another question: deadrise measured where? If the angle
between a horizontal plane tangent to the keel and the chine is
measured just aft of the bow, most modern boats will measure around
45° or more. If measured just forward of the stern, the deadrise may
be as little as 5°. The days when deep-V hulls carried the same high
angle of deadrise nearly constantly from bow to stern is long gone.
Why? Because they didn't perform very well."

Hey John, this is a pretty fair explanation of the reason for using a
measurement somewhat forward of the transom for a published spec...It's
not so much of an average angle, as it is the angle at the widest
"wetted" area of the hull at speed..the low deadrise at stern provides
stability, especially with engines mounted well aft.. a high angle
carried all the way aft tends to make a boat "porpoise" at speed...too
low an angle causes instability when turning at speet, too rapid a
transition and you get a boat that meanders at low speed, and can
develop low pressure areas at speed that can negate lift or planing
ability..


The definition you provided makes perfect sense! I've just always thought
incorrectly. Thanks for screwing my head on properly.
--
John H

******Have a spectacular day!******

Evidently deadrise must only refer to the angle of the hull at no
specific point. Every spec I've read in new boat catalogs reference the
"deadrise at transom". This definition agrees:

http://www.boats.com/glossary/D.jsp

There are others that refer to the widest part of the boat. I guess the
moral of this story is no one can simply refer to "deadrise" without
adding the point on the hull where it was measured.

Dan

41. markvictor
Jan 21, 9:31 am show options
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From: "markvictor" - Find messages by this
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Date: 21 Jan 2006 09:31:38 -0800
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Subject: Boaters Jeopardy
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"The first part of the answer in determining how deadrise affects
performance is another question: deadrise measured where? If the angle
between a horizontal plane tangent to the keel and the chine is
measured just aft of the bow, most modern boats will measure around
45° or more. If measured just forward of the stern, the deadrise may
be as little as 5°. The days when deep-V hulls carried the same high
angle of deadrise nearly constantly from bow to stern is long gone.
Why? Because they didn't perform very well."

Hey John, this is a pretty fair explanation of the reason for using a
measurement somewhat forward of the transom for a published spec...It's
not so much of an average angle, as it is the angle at the widest
"wetted" area of the hull at speed..the low deadrise at the stern
provides
stability, especially with engines mounted well aft.. a high angle
carried all the way aft tends to make a boat "porpoise" at speed...too
low an angle causes instability when turning at speed, too rapid a
transition and you get a boat that meanders at low speed, and can
develop low pressure areas at speed that can negate lift or planing
ability..

Reply

"The first part of the answer in determining how deadrise affects
performance is another question: deadrise measured where? If the angle
between a horizontal plane tangent to the keel and the chine is
measured just aft of the bow, most modern boats will measure around
45° or more. If measured just forward of the stern, the deadrise may
be as little as 5°. The days when deep-V hulls carried the same high
angle of deadrise nearly constantly from bow to stern is long gone.
Why? Because they didn't perform very well."

Hey John, this is a pretty fair explanation of the reason for using a
measurement somewhat forward of the transom for a published spec...It's
not so much of an average angle, as it is the angle at the widest
"wetted" area of the hull at speed..the low deadrise at the stern
provides
stability, especially with engines mounted well aft.. a high angle
carried all the way aft tends to make a boat "porpoise" at speed...too
low an angle causes instability when turning at speed, too rapid a
transition and you get a boat that meanders at low speed, and can
develop low pressure areas at speed that can negate lift or planing
ability.