otnmbrd wrote:
Will be interesting to find out what happened. If someone accidently hit
the wrong button during a course change it's one thing, but if there is a
control glitch..... yikes.

Does this ship steerable props (such as the Azi-Pod)? If so,
then there's no way the helmsman could make the ship roll no
matter how hard he turned.


Other possible contributor would be "stabilizers".

Bingo

As for "top heavy".... she does look it, but the reality is that she
probably isn't.


I dunno, the ABS has recently decided that use of active
stabilizers counts for stability. Maybe they have some sort
of absolute guarantee that the system never goes down? In
any event, the standards for ship's metacenter has been
changed. Maybe when one of them falls on it's side and the
crew has to right it like a Laser,
http://www.willamettesailingclub.com...os/capsize.jpg
the standards will change back again?

Fresh Breezes- Doug King

DSK wrote:
otnmbrd wrote:
Will be interesting to find out what happened. If someone accidently hit
the wrong button during a course change it's one thing, but if there is a
control glitch..... yikes.

Does this ship steerable props (such as the Azi-Pod)? If so,
then there's no way the helmsman could make the ship roll no
matter how hard he turned.


What? I call BS.!

Are you telling me could not induce a roll on ship with pods? These are
electric outboards engnes in pods, the pods turn so rudders are not
needed. I say... I could make a ship roll faster and harder with pods
if she has any weight up top. Its a matter of sway, not propulsion.

Joe


Other possible contributor would be "stabilizers".

Bingo

As for "top heavy".... she does look it, but the reality is that she
probably isn't.


I dunno, the ABS has recently decided that use of active
stabilizers counts for stability. Maybe they have some sort
of absolute guarantee that the system never goes down? In
any event, the standards for ship's metacenter has been
changed. Maybe when one of them falls on it's side and the
crew has to right it like a Laser,
http://www.willamettesailingclub.com...os/capsize.jpg
the standards will change back again?

Fresh Breezes- Doug King

Does this ship steerable props (such as the Azi-Pod)? If so,
then there's no way the helmsman could make the ship roll no
matter how hard he turned.


Joe wrote:
What? I call BS.!

Are you telling me could not induce a roll on ship with pods?

I don't know if it's impossible to make the ship roll *any*
but it will certainly roll a heck of a lot less.


... Its a matter of sway, not propulsion.


No, it's a matter of forces around the centers of mass &
resistance. A rudder will make a ship roll because it is far
down below the waterline, and it only creates a force in one
direction. With an Azipod the ship is pulled (or pushed)
into a turn with much less heeling force generated. It's one
of the purposes of building it that way.

I suppose it follows that if the azipod (or any other
steerable prop) is used the exact opposite of how it should
be, the ship could roll even more... maybe that's what happened!

Anyway, google up the design brief on azipods if you think
I'm BSing.

Fresh Breezes- Doug King

DSK wrote:

Yeah sure agreed

Anyway, google up the design brief on azipods if you think
I'm BSing.


Sure the design is superior in moving any direction. The reason pods
are used on ships is to avoid harbor tugs and allow tight manuvering in
harbor, and they are a more fuel efficent diesel electric set-up. Has
nothing to do with stability of a cruise ship IMO.

Little experment, take a 4x8 sheet of plywood on edge, set course
straight down the street, then as you get up to speed push the aft
section left or right and see how the plywood sways. You turn something
that heavy fast it is going to sway, do a quick S you could induce a
very nice (even un-expected and deadly) roll with such a top heavy pig.

Joe


Fresh Breezes- Doug King

Anyway, google up the design brief on azipods if you think
I'm BSing.


Joe wrote:
Sure the design is superior in moving any direction. The reason pods
are used on ships is to avoid harbor tugs and allow tight manuvering in
harbor, and they are a more fuel efficent diesel electric set-up. Has
nothing to do with stability of a cruise ship IMO.


That's not the main purpose, agreed.
But it is a fact that an azipod will induce less rolling
moment on a ship because it can generate a force along any
vector, not just sideways very far below the ship's center
of mass like a rudder.


Little experment, take a 4x8 sheet of plywood on edge, set course
straight down the street, then as you get up to speed push the aft
section left or right and see how the plywood sways. You turn something
that heavy fast it is going to sway,

Wrong.

It sways because the force is not aligned on the horizontal
axis. In order to turn the object, the force must be either
forward or aft of the center of lateral resistance, and
since that's not necessarily the same place as the center of
mass.

In your example, will the plywood sway in the exact same
manner if the plywood is pushed from the bottom or from the
top? How about if it's pulled instead of pushed? How about
if the push (or pull) to turn it is aligned exactly along
the vertical center?

... do a quick S you could induce a
very nice (even un-expected and deadly) roll with such a top heavy pig.


I thought you and OTN were saying they're not that top
heavy? Anyway, a containership stacked as high as the bridge
will be very top heavy too.

DSK

DSK wrote:


I thought you and OTN were saying they're not that top
heavy? Anyway, a containership stacked as high as the bridge
will be very top heavy too.


Not me! Otn said that.

One look at that monster with all it's air borne swimming pools and
buffet carts one can assume she sways like a french girls ass if great
care in not taken to avoid it.

Joe

..
DSK

"DSK" wrote in message
news
otnmbrd wrote:
Will be interesting to find out what happened. If someone accidently hit
the wrong button during a course change it's one thing, but if there is a
control glitch..... yikes.

Does this ship steerable props (such as the Azi-Pod)? If so, then there's
no way the helmsman could make the ship roll no matter how hard he turned.


Would tend to disagree here. You put a ship into a hard turn, the mass of
the ship is going to make it lean towards the outside line of the
turn.....no matter what the propulsion.
Now, I also doubt that the angle they achieved was really as high as
speculated (that high up and it will seem much worse that it is) but it
doesn't take much of a roll which is not expected to start throwing people
and things around, but back to your point.... although Z-drive and azipod
are different, I know a Z-drive will lay itself over in a hard turn but I've
never been on an azipod unit when making one and I would have to think that
on these ships, the stabilizer (if working) would tend to minimize the roll
angle ..... a lot of speculation on my part and why I'm going to be
interested to hear the final reports.


Other possible contributor would be "stabilizers".

Bingo

As for "top heavy".... she does look it, but the reality is that she
probably isn't.


I dunno, the ABS has recently decided that use of active stabilizers
counts for stability. Maybe they have some sort of absolute guarantee that
the system never goes down? In any event, the standards for ship's
metacenter has been changed. Maybe when one of them falls on it's side and
the crew has to right it like a Laser,
http://www.willamettesailingclub.com...os/capsize.jpg
the standards will change back again?

Counts in what way? I can't imagine that it in anyway could count for
initial or damage stability, but may allow a slightly reduced one under
certain operating conditions. As for "top heavy", be it a cruise ship or a
car carrier most of that space is relatively empty (i.e., not a lot of solid
weight) so that looks aside I'm betting they still have a pretty good GM
..... course, as with the car carrier Tricolor, it doesn't take much water to
play hell with that GM.


otn