DDG-1000 Stability
John Dallman
destroyers, I wondered what they were like, took a look at the info on
www.globalsecurity.org and began to wonder about their stability. My
knowledge of this is confined to having read a couple of books on
shipbuilding, but is not actually zero. A little Googling reveals that
I'm by no means alone in this worry, but that the USN says they meet all
the applicable safety standards.
OK, I'll believe that for the sake of argument. But the tumblehome hull
means that as they start to heel, their righting moment won't grow as
fast as a conventional hull. So if they actually meet safety standards
in plausible damaged conditions, they must be very "stiff" undamaged -
with their centres of buoyancy a long way above their centres of gravity
- which means their normal roll in waves will be short and sharp. Unless
someone's been very clever indeed. Such stiffness isn't going to be a
problem for weapons use, with modern fire-control, but it may be a bit
hard on the crew.
Presumably stability figures and graphs for current and planned USN
ships are classified information?
--
John Dallman, j...@cix.co.uk, HTML mail is treated as probable spam.
dott.Piergiorgio
> Presumably stability figures and graphs for current and planned USN
> ships are classified information?
In some cases (nuclear ships) there's nuch less architectural data
publicly available; but in general a sailor worth his salt can get the
seakeeping & stability qualities of a ship at a glance on pier, more so
if the ship was moored Mediterranean-style, that is, by stern.
So, for example, isn't that secret that the Ticos are a bit top-heavy
because everyone in the field can observe & evaluate their roll.
ISTR recently here was a lively discussion of actual capability of the
Ticos in the north atlantic conditions.
Personally, my doubts on Zumwalts are about the wetness of the no,1 gun
& forward VLSs, a tumblehome coupled with a ram bow is the sure way for
a wery wet fore deck.....
Best regards from Italy,
Dott. Piergiorgio.
g lof2
like one.
The answer to the first question is that with out help the DDG-1000
will be stiff according to published reports, but only when not
underway. When underway they use automatic stabizers like cruise ships
do that counteracts the roll.
John Dallman
<a1ebbd71-eccf-4dd1...@r35g2000prm.googlegroups.com>,
glof...@msn.com (g lof2) wrote:
> On Aug 16, 1:22 pm, "dott.Piergiorgio"
> <dott.PiergiorgioNI...@KAIGUN.fastwebnet.it> wrote:
> > John Dallman ha scritto:
> > Personally, my doubts on Zumwalts are about the wetness of the no,1
> > gun & forward VLSs, a tumblehome coupled with a ram bow is the sure
> > way for a wery wet fore deck.....
Indeed. Given their main purpose is supposed to be land attack, it might
be claimed that they won't be trying to use their weapons in weather
conditions too bad for a landing.
> The answer to the first question is that without help the DDG-1000
> will be stiff according to published reports, but only when not
> underway. When underway they use automatic stabizers like cruise ships
> do that counteracts the roll.
Right. Of course, if you lose the stabilisers to damage, your damage
control in bad weather just got rather harder. But then, I'm used to
British Isles weather, where you can simply assume a gale will be
blowing any time you want to do anything at sea, and rarely be wrong.
These ships do rather seem like a leap of faith, where lots of new
technologies all have to work right. I'm not surprised that the USN has
got cold feet, considering their cost.
g lof2
> In article
> <a1ebbd71-eccf-4dd1-9470-28a5d1d02...@r35g2000prm.googlegroups.com>,
>
> glof_...@msn.com (g lof2) wrote:
> > On Aug 16, 1:22 pm, "dott.Piergiorgio"
> > <dott.PiergiorgioNI...@KAIGUN.fastwebnet.it> wrote:
> > > John Dallman ha scritto:
> > > Personally, my doubts on Zumwalts are about the wetness of the no,1
> > > gun & forward VLSs, a tumblehome coupled with a ram bow is the sure
> > > way for a wery wet fore deck.....
>
> Indeed. Given their main purpose is supposed to be land attack, it might
> be claimed that they won't be trying to use their weapons in weather
> conditions too bad for a landing.
>
> > The answer to the first question is that without help the DDG-1000
> > will be stiff according to published reports, but only when not
> > underway. When underway they use automatic stabizers like cruise ships
> > do that counteracts the roll.
>
> Right. Of course, if you lose the stabilisers to damage, your damage
> control in bad weather just got rather harder. But then, I'm used to
> British Isles weather, where you can simply assume a gale will be
> blowing any time you want to do anything at sea, and rarely be wrong.
>
> These ships do rather seem like a leap of faith, where lots of new
> technologies all have to work right. I'm not surprised that the USN has
> got cold feet, considering their cost.
>
with sails if the engines break down, and masses of AA guns if the
missile system fail?
OK I will repeat what I told other people.
Engineering is the art of compromize, trading one thing for another.
The hull of the Zumwalt is designed to reduce greatly the odds it will
hit by anti-ship missile. Modern anti-ship missiles are estimated to
have a +50% fatality ratio, that is if it hits it target, it will
kill the ship over half the time, so avoiding getting hit is much more
important than possibly survivally of the ship after it is damaged.
Therefore any argument that we should not build the the Zumwalt
because of their hull shape is basic on ignorance of the engineering
facts, and not one any real knowledge of the design history.
John Dallman
<71088938-f745-4c59...@r15g2000prd.googlegroups.com>,
glof...@msn.com (g lof2) wrote:
> The hull of the Zumwalt is designed to reduce greatly the odds it will
> hit by anti-ship missile. Modern anti-ship missiles are estimated to
> have a +50% fatality ratio, that is if it hits it target, it will
> kill the ship over half the time, so avoiding getting hit is much more
> important than possibly survivally of the ship after it is damaged.
Makes good sense if you're sure that is your major threat. Over-
specialising in defence against one threat has been known to cause
designers to neglect vulnerability to other threats. Uncharted rocks
don't care about radar cross-sections, and neither do suicide boats in
port. Ships have to be functional ships as well as weapon systems.
> Therefore any argument that we should not build the the Zumwalt
> because of their hull shape is basic on ignorance of the engineering
> facts, and not one any real knowledge of the design history.
I wasn't arguing that. I didn't have the benefit of reading your earlier
posts on the subject. I was originally expressing reservations and
asking for information; having got some, I acknowledged that the USN's
decision to stop after two ships may not be entirely crazy. Once it's
been seen how they work in practice, some more can be bought.
This might turn out like USN submarine procurement: the SSN-21 Seawolf
class was intended to be the replacement for Los Angeles boats, but
proved to be too expensive, so the Virginias, using more developed
technology at lower cost, ended up being bought.
Tiger
The complaints sems to be over sea keeping, not damage control. A ship
is more likely to fight the sea than a anti ship missile.
g lof2
>
> glof_...@msn.com (g lof2) wrote:
> > The hull of the Zumwalt is designed to reduce greatly the odds it will
> > hit by anti-ship missile. Modern anti-ship missiles are estimated to
> > have a +50% fatality ratio, that is if it hits it target, it will
> > kill the ship over half the time, so avoiding getting hit is much more
> > important than possibly survivally of the ship after it is damaged.
>
> Makes good sense if you're sure that is your major threat. Over-
> specialising in defence against one threat has been known to cause
> designers to neglect vulnerability to other threats. Uncharted rocks
> don't care about radar cross-sections, and neither do suicide boats in
> port. Ships have to be functional ships as well as weapon systems.
>
and not a major one. Remember that the Zumwalts are far larger than
their predecessors, have better compartmentalization, and superior
double hull design. All this because they are warship, and good old
under the kell shots (mines and torpedoes) scare sailors more than
missile any day. So I assure you, the NARCH (Naval Archietects) did
considers things flooding and big holes in the side when the designed
the Zumwalts.
The worst critic can come up with so far, is that if the ship is not
under way, in heavy following seas, then the ship will pitch
excessivily, but then so will most sail boats.
> > Therefore any argument that we should not build the the Zumwalt
> > because of their hull shape is basic on ignorance of the engineering
> > facts, and not one any real knowledge of the design history.
>
> I wasn't arguing that. I didn't have the benefit of reading your earlier
> posts on the subject. I was originally expressing reservations and
> asking for information; having got some, I acknowledged that the USN's
> decision to stop after two ships may not be entirely crazy. Once it's
> been seen how they work in practice, some more can be bought.
>
But only with a great deal money. Stopping the Zumwalt will force the
navy to spend billions building ships they not only don't need, but
that they can not afford to run in the long term. In fact I am
considered that we built too many Burke types already, almost 2/3 of
your first line ship are Burkes, and contra to what some would have
you believe, thay are far from perfect warships. They have flaws in
their hulls, they main drive is obsolete and expose them to those many
of the danger you worry about. An if an enemy discover a major defect
they can exploit, then the USN may find itself with out the majority
of it surface fighting power.
Now I an not saying the Zumwalts are perfect, their design has taken a
lot of hits, and engineering is the are of compromise. If I had them,
thay still have all their missile and magazine, their original four
shafts, the second full helo pad plus third hanger, and that big boat
hanger. That would have made them far more cost effective than the
current design. Ans as ships go, it will be hard ride, but it a
warship after all, not a cruise ship.
> This might turn out like USN submarine procurement: the SSN-21 Seawolf
> class was intended to be the replacement for Los Angeles boats, but
> proved to be too expensive, so the Virginias, using more developed
> technology at lower cost, ended up being bought.
>
I not to sure about that, the development cost of the Virginias would
have paid for alot of Seawolfs, which are still better boats according
to some people I read (their opinions not necessarially mine.) Sure
the Virginia technology is new, but it that does not make it better.
And we lost a lot of possible improvments to weapons by abandoning the
Seawolfs larger weapons rooms and tubes.