Actively variable deadrise
 

On Mar 21, 9:00*pm, Frogwatch wrote:
On Mar 21, 7:22 pm, Monkey Butler wrote:





- Show quoted text -

In theory the concept of mechanically variable deadrise should work
but in practice the complexity is too *much of an obstacle in a small
boat so it makes more sense to have a different boat design for
different conditions and/or operational parameters. In a larger craft
the objective is more easily achieved with designs such as SWATH,
catamarans, or hydrofoils. Current high speed ferries are good
examples, and the Russians have built some neat hydrofoils .

I took the Westlawn course for my own entertainment and while much of
the facts and figures that I learned have been lost most of the
concepts are still clear. *A couple of points… At rest your boat stays
above the surface of the water because of the hull’s buoyancy and by
virtue of its static displacement. Once you start moving your hull
will generate a series of waves in the medium that it is floating in.
At a point called hull speed your boat will be traveling in a trough
between the bow wave and the stern wave. As you increase speed further
the bow will rise as it attempts to climb the bow wave and at some
point Newton’s Third Law will kick in and the action of the water
meeting you hull surface will result in a equal reaction that will
lift the hull of your boat. *Then, at some point the flow of water
against the hull will separate from one stream flowing under your hull
into two, one flowing under the hull and another flowing forward of
the hull as spray. This is the stagnation point, the point where
maximum lift is generated. Any water striking the hull at this point
is converted into 100 percent lift. Anything forward is wasted as
spray and anything aft will act on the rear planing surface and affect
the angle of attack. As speed increases the stagnation point will move
aft and at the same time the CG of the hull will move up. (BTW, This
is where trim tabs come in. They can be used to adjust the trimming
force and thus the angle of attack, but they will not create lift…).
Eventually the weight of your boat is no longer being supported by the
displacement of water but by the dynamic force of the water striking
its planing surface. *A perfectly flat bottom means that the lift is
vertical. A vee bottom wastes a percentage of the energy as spray
deflected to the side.

If any of the above makes sense then it would seem that we would need
to adjust the deadrise at the stagnation point to avoid pounding. The
problem is that with any small boat running in a sea this point moves
fore and aft on the hull due to the waves that it encounters. Most
modern hulls deal with this by having a sharper vee at the bow and
less dead rise at the stern so I guess the answer to your original
question is that your radical idea has already been incorporated into
almost every hull design! In reality we know that every hull is a
compromise and the overall deadrise is always a tradeoff between sea
keeping and efficiency. I know that Seacraft for one advertised
variable deadrise as being a change in angle from keel to chine but in
normal marine architects language this is a term that refers to the
variation in dead rise angle measured at different points from bow to
stern. Constant dead rise hulls are referred to as Monohedron versus a
variable dead rise called a warped plane. Warped planes have their
limits as far as how much you can “warp” them before you trade off
performance especially if we are talking “Miami Vice” type boats.

Lobster boats or Downeast designs stretch the warped plane idea. They
have a very sharp entry forward but an almost flat bottom aft. *This
limits their performance but it is the main reason for their famed
ride. Round bilges and full keels have nothing to do with it.

Steve P.

Steve:

Ok, I got most of that, but, why does a boat make a stern wave?- Hide quoted text -

- Show quoted text -

???

Why wouldn't it?

Actively variable deadrise
 

On Sat, 21 Mar 2009 18:00:36 -0700 (PDT), Frogwatch
wrote:

why does a boat make a stern wave?

Not very scientific but I view it as sort of a rebound effect as the
water that has been displaced downward by passage of the hull, now
springs back up behind the boat and overshoots the surface due to
inertia.

Actively variable deadrise
 

On Mar 22, 12:26*am, Wayne.B wrote:
On Sat, 21 Mar 2009 18:00:36 -0700 (PDT), Frogwatch

wrote:
why does a boat make a stern wave?

Not very scientific but I view it as sort of a rebound effect as the
water that has been displaced downward by passage of the hull, now
springs back up behind the boat and overshoots the surface due to
inertia.

Actively variable deadrise
 

On Mar 22, 12:26*am, Wayne.B wrote:
On Sat, 21 Mar 2009 18:00:36 -0700 (PDT), Frogwatch

wrote:
why does a boat make a stern wave?

Not very scientific but I view it as sort of a rebound effect as the
water that has been displaced downward by passage of the hull, now
springs back up behind the boat and overshoots the surface due to
inertia.

Hope this isn't a double post, Goggle Groups is a PITA


Wayne, this is true but you can’t concentrate on just the stern wave.
Any time you disturb a fluid you will transfer the energy via a series
of waves. Drop a stone in a pool, does it create just one wave? No,
and neither does a boat hull.

I find it fascinating to observe the “wake” left by a small duck
paddling along in glass smooth water on a calm morning. If you look
at the total amount of surface area that he can affect it is amazing
considering his size and weight. If he swims by another duck then that
duck will bob up and down in his wake so duck number two must be
absorbing the wave energy that duck one put into the water, right? But
if duck one paddles through a flotilla of one hundred ducks they all
bob up and down. Go figure.

Actively variable deadrise
 

On Mar 21, 2:24*pm, wrote:
On Mar 21, 1:27*pm, "Don White" wrote:





wrote in message

....
On Mar 21, 12:28 pm, "Don White" wrote:

wrote in message

....
On Mar 20, 10:25 am, "Don White" wrote:

wrote in message

...
On Mar 19, 5:24 pm, "Don White" wrote:

"Vic Smith" wrote in message

.. .

Not bad when you consider it took Edward G. Robinson 606 tries
before
he arrived at the "magic bullet" cure for syphilis.
Killed a lot of people doing it too.

--Vic

So it's not a good idea for JohnnyPrepH to lubricate/winterize his
outboards
cylinders with WD-40?

Cylinders don't have bearings, idiot.

************************************************

I didn't say they did jackass.- Hide quoted text -

- Show quoted text -

Oh, I take it you didn't understand the sentence you quoted,
then......
Here is what was said:
"Just like WD-40 is still killing bearings."

To which you idiotically replied....

So it's not a good idea for JohnnyPrepH to lubricate/winterize his
outboards cylinders with WD-40?

So......why did you make such a statement directly replying to a
statement about....BEARINGS?

************************************************** *

For the sake of the children.......quit growin' & smokin' that Georgia
Bud!- Hide quoted text -

- Show quoted text -

What on earth are you babbling about now? You've learned from your
lover/master/clone Harry how to deflect with idiotic comments when
someone shows just how stupid you are. Or do you have some mental
incapacity that makes you wander off on different tangents, not being
able to keep on the topic at hand?

************************************

Not at all. I just deal with the facts as they are revealed to me.
Drop the weed...for the kids!- Hide quoted text -

- Show quoted text -

Well, then, give me the facts. WHAT WEED, dummy? What "facts" were
"revealed" to you? By whom? Who told you I smoke "grow and smoke"
ANYTHING? We'll see how good you do with "facts"......- Hide quoted text -

- Show quoted text -

crickets............

Actively variable deadrise
 

On Sat, 21 Mar 2009 23:43:31 -0700 (PDT), Monkey Butler
wrote:

On Mar 22, 12:26*am, Wayne.B wrote:
On Sat, 21 Mar 2009 18:00:36 -0700 (PDT), Frogwatch

wrote:
why does a boat make a stern wave?

Not very scientific but I view it as sort of a rebound effect as the
water that has been displaced downward by passage of the hull, now
springs back up behind the boat and overshoots the surface due to
inertia.

Hope this isn't a double post, Goggle Groups is a PITA


Wayne, this is true but you can’t concentrate on just the stern wave.
Any time you disturb a fluid you will transfer the energy via a series
of waves. Drop a stone in a pool, does it create just one wave? No,
and neither does a boat hull.

I find it fascinating to observe the “wake” left by a small duck
paddling along in glass smooth water on a calm morning. If you look
at the total amount of surface area that he can affect it is amazing
considering his size and weight. If he swims by another duck then that
duck will bob up and down in his wake so duck number two must be
absorbing the wave energy that duck one put into the water, right? But
if duck one paddles through a flotilla of one hundred ducks they all
bob up and down. Go figure.

It's classic harmonic oscillation and wave propagation. The first
rebound creates the first wave, displaced water over shoots and
creates the second wave, etc. Since it is a damped oscillation,
limited by the viscosity of the fluid and energy imparted to the wave
train, the number of waves created is relatively small.

Actively variable deadrise
 

Why not some mechanism that would consist of another
outer variable hull layer that would be hinged at the chines allowing
the keel portion to move downward to increase deadrise. It would have
a flexible stiff plastic piece at the front to keep water out of the
area between the two hulls. Is this simply too complex for too little
benefit?
The semi-rigid inflatable boats have much of the operational pieces you
would need to test out a variable deadrise hull; i.e, a planing hull and the
inflatable bladders on the sides.

You would take a regular boat hull and build on an extended keel. Take your
semi-rigid hull, cut it in half, attach a hinge to the centerline and then
attach that hinge to the extended keel of the test boat.
Then, by changing the pressure on the bladders, the rigid part of the add-on
hull would be forced down into a flatter bottom with less deadrise. The
beauty of the design is that you could change the deadrise for existing
conditions, and the bladders would add an extra amount of cushioning from
wave hits.
You would of course need to experiment with hull and bladder shapes and
sizes, but it might work.

An energy-saving green hull design like this might be elgible for some of
that stimulus money, no?

Actively variable deadrise
 

"Floyd" wrote in message
...
Why not some mechanism that would consist of another
outer variable hull layer that would be hinged at the chines allowing
the keel portion to move downward to increase deadrise. It would have
a flexible stiff plastic piece at the front to keep water out of the
area between the two hulls. Is this simply too complex for too little
benefit?
The semi-rigid inflatable boats have much of the operational pieces you
would need to test out a variable deadrise hull; i.e, a planing hull and
the inflatable bladders on the sides.

You would take a regular boat hull and build on an extended keel. Take
your semi-rigid hull, cut it in half, attach a hinge to the centerline
and then attach that hinge to the extended keel of the test boat.
Then, by changing the pressure on the bladders, the rigid part of the
add-on hull would be forced down into a flatter bottom with less deadrise.
The beauty of the design is that you could change the deadrise for
existing conditions, and the bladders would add an extra amount of
cushioning from wave hits.
You would of course need to experiment with hull and bladder shapes and
sizes, but it might work.

An energy-saving green hull design like this might be elgible for some of
that stimulus money, no?


Wonder if you could consider the wings that the America's Cup boats have on
the keel as an Active Variable Deadrise device?

Actively variable deadrise
 

On Tue, 24 Mar 2009 17:02:21 -0800, "Calif Bill"
wrote:

Wonder if you could consider the wings that the America's Cup boats have on
the keel as an Active Variable Deadrise device?

Don't think so. The wings on AC boats were a rule beating device
which allowed the designer to increase the righting moment/stability
without exceeding the draft limit imposed by the 12 meter rule.

A lot of cruising boat builders thought if would be trendy if they
offered a wing keel also but then people found out what happens when
you run aground in a boat that increases its draft as you incline it.

Actively variable deadrise
 

"Wayne.B" wrote in message
...
On Tue, 24 Mar 2009 17:02:21 -0800, "Calif Bill"
wrote:

Wonder if you could consider the wings that the America's Cup boats have
on
the keel as an Active Variable Deadrise device?

Don't think so. The wings on AC boats were a rule beating device
which allowed the designer to increase the righting moment/stability
without exceeding the draft limit imposed by the 12 meter rule.

A lot of cruising boat builders thought if would be trendy if they
offered a wing keel also but then people found out what happens when
you run aground in a boat that increases its draft as you incline it.


I know what they do. But was wondering if they could be made movable and be
equivalent to changing the deadrise.