HK wrote in
:

Jim Willemin wrote:
Frogwatch wrote in
news:571e39b1-f812-459a-b9e6-
:

It seems that deadrise has a radical effect on the ability of a boat
to get on plane quickly and thus use less fuel. More deadrise makes
a boat punch through waves better but increases draft and reduces
fuel economy in smaller seas. I assume that variable deadrise has
been tried. Of course there are boats that try to use hull shape to
accomodate varying conditions but not too successfully.
My Tolman has about 10 degree deadrise and is very light so is very
fuel efficient but pounds a lot in chop so I have to slow down to
about 12 kts. 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?


Having pondered this for a couple of days, I am struck by the problem
of changing the area of the floor between the keel and the chine.
This might be tractable near the transom (overlapping leaves,
perhaps, kinda like a 'sliding lapstrake' construction), but as you
get near the stem you gotta worry about major changes in geometry as
well as area. I imagine a really clever designer could do it. I
suppose the question is where in the hull would variable deadrise be
most effective in the transition to planing? That might make an
interesting thesis for someone...



Bring a lifejacket.


I was thinking more of models in a wavetank. But seriously: where in
the hull is deadrise most important to achieving planing status? Is it
in the forward third, the midships third, or the aft third? Since
planing is essentially the result of climbing one's own bow wake, or the
wave whose wavelength is equal to your waterline length, my hunch is
that the geometry near the stem is probably most significant in
acheiving planing. But there has to be some kind of optimum - it seems
to me that a flatiron skiff, say, would take more energy to achieve
planing mode than a runabout of identical length. So if the critical
region is in the forward third of the hull, where major changes in both
hull geometry and hull area occur as you mess with deadrise, it seems to
me probably not worth the effort.

Jim Willemin wrote:
HK wrote in
:

Jim Willemin wrote:
Frogwatch wrote in
news:571e39b1-f812-459a-b9e6-
:

It seems that deadrise has a radical effect on the ability of a boat
to get on plane quickly and thus use less fuel. More deadrise makes
a boat punch through waves better but increases draft and reduces
fuel economy in smaller seas. I assume that variable deadrise has
been tried. Of course there are boats that try to use hull shape to
accomodate varying conditions but not too successfully.
My Tolman has about 10 degree deadrise and is very light so is very
fuel efficient but pounds a lot in chop so I have to slow down to
about 12 kts. 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?

Having pondered this for a couple of days, I am struck by the problem
of changing the area of the floor between the keel and the chine.
This might be tractable near the transom (overlapping leaves,
perhaps, kinda like a 'sliding lapstrake' construction), but as you
get near the stem you gotta worry about major changes in geometry as
well as area. I imagine a really clever designer could do it. I
suppose the question is where in the hull would variable deadrise be
most effective in the transition to planing? That might make an
interesting thesis for someone...


Bring a lifejacket.


I was thinking more of models in a wavetank. But seriously: where in
the hull is deadrise most important to achieving planing status? Is it
in the forward third, the midships third, or the aft third? Since
planing is essentially the result of climbing one's own bow wake, or the
wave whose wavelength is equal to your waterline length, my hunch is
that the geometry near the stem is probably most significant in
acheiving planing. But there has to be some kind of optimum - it seems
to me that a flatiron skiff, say, would take more energy to achieve
planing mode than a runabout of identical length. So if the critical
region is in the forward third of the hull, where major changes in both
hull geometry and hull area occur as you mess with deadrise, it seems to
me probably not worth the effort.

Deadrise isn't important in achieving planing status: a flat-bottomed
boat will plane just fine. The more deadrise, the more power it takes to
get a boat up on plane.

On Fri, 20 Mar 2009 12:25:30 -0400, HK wrote:

Jim Willemin wrote:
HK wrote in
:

Jim Willemin wrote:
Frogwatch wrote in
news:571e39b1-f812-459a-b9e6-
:

It seems that deadrise has a radical effect on the ability of a boat
to get on plane quickly and thus use less fuel. More deadrise makes
a boat punch through waves better but increases draft and reduces
fuel economy in smaller seas. I assume that variable deadrise has
been tried. Of course there are boats that try to use hull shape to
accomodate varying conditions but not too successfully.
My Tolman has about 10 degree deadrise and is very light so is very
fuel efficient but pounds a lot in chop so I have to slow down to
about 12 kts. 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?

Having pondered this for a couple of days, I am struck by the problem
of changing the area of the floor between the keel and the chine.
This might be tractable near the transom (overlapping leaves,
perhaps, kinda like a 'sliding lapstrake' construction), but as you
get near the stem you gotta worry about major changes in geometry as
well as area. I imagine a really clever designer could do it. I
suppose the question is where in the hull would variable deadrise be
most effective in the transition to planing? That might make an
interesting thesis for someone...


Bring a lifejacket.


I was thinking more of models in a wavetank. But seriously: where in
the hull is deadrise most important to achieving planing status? Is it
in the forward third, the midships third, or the aft third? Since
planing is essentially the result of climbing one's own bow wake, or the
wave whose wavelength is equal to your waterline length, my hunch is
that the geometry near the stem is probably most significant in
acheiving planing. But there has to be some kind of optimum - it seems
to me that a flatiron skiff, say, would take more energy to achieve
planing mode than a runabout of identical length. So if the critical
region is in the forward third of the hull, where major changes in both
hull geometry and hull area occur as you mess with deadrise, it seems to
me probably not worth the effort.

Deadrise isn't important in achieving planing status: a flat-bottomed
boat will plane just fine. The more deadrise, the more power it takes to
get a boat up on plane.

....therefore, deadrise *is* important in achieving planing status. The
more deadrise, the more difficult to achieve plane.

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?

"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?

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.

"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.

Calif Bill wrote:
"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.



Winged keels with movable wings and winglets appeared in a later
generation of America's Cup yachts.

How about a hydrofoil boat...with variable and adjustable "deadrise" on
the foils?