From: gherbert@crl.crl.com (George Herbert)
Newsgroups: sci.military.naval
Subject: Re: Titanium sub
Date: 31 Jan 2000 12:27:02 -0800

Andy McCruden  <Useless@beyond-comprehension.fsnet.co.uk> wrote:
>Iberian wrote:
>> >       I also remember reading someplace that American companies were
>> > incapable of producing a welded titanium hull.  Once again, True or False?
>>
>> Probably false.
>
>Actaully It is about 50-50, they would be incable of stating to build
>one tomorow, but the capabiltiy could have been realistically developed
>in a relatively short timescale IIRC

There's plenty of Titanium welding equipment out there (same stuff you
weld Aluminum with), but almost nobody qualified to weld it compared to
experience with Steel or Aluminum.  You'd have to retrain all the welders.
The skills exist, we know *how* to do it, but you need to have a thousand
shipyard skilled welders with the skill, not a few (hundreds?) in aerospace
and specialty metal shops.

>> >       If titanium hulls are superior, why do we not produce one?
>>
>> I'm not totally familiar with the American military budget or policy, but if
>> things over there are similar than in Europe, the only realistic answer is:
>> Money. In addition to that, submarines are built to fulfill and overall
>> strategic plan/policy. In that strategic planning, the capability of
>> reaching 1500 m. may be not worthwhile in a strict cost/capability relation.
>
>Also titanium hulls are far less resitant to shock as titanium is much
>"stiffer" than Steel and warships tend to get subjected to shock quite a
>bit in combat.

By that logic, Aluminum would be even worse.  I haven't heard of any
particular problems with Aluminum hulled vessels passing shock testing...
Anyone have better info?

The number one issue of course is cost.  Titanium sponge (not alloy)
is over $5/lb.  Good Ti alloy plating is up to twice that.  Welding it
takes longer than welding steel, uses different skills, has to be
done under inert gases like CO2 or Argon or Helium (not Nitrogen,
Titanium burns in Nitrogen...).  The hull material cost is fairly
low percentage of fab cost for warships, but Titanium would probably
at least double the manhours required to fabricate the hull and add
something like 50% more for additional materials costs.  With prior
classes, the hull cost was a large fraction of the vessel... it doesn't
make much sense to add more systems by saving hull weight when it will
cost more than the gain.  Current ships might be a different case,
but I haven't seen any serious proposals to go to Titanium.


-george william herbert
gherbert@crl.com

From: gherbert@crl.crl.com (George Herbert)
Newsgroups: sci.military.naval
Subject: Re: Titanium sub
Date: 31 Jan 2000 15:21:51 -0800

Andrew C. Toppan <actoppan@gwi.net> wrote:
>Len Maxwell (lenlee@waypt.com) was seen to write:
>>       I have read that the Russian Alfa class could dive much deeper and
>> was faster than American subs, largely due to having a welded titanium
>> hull.  True or false?
>
>Deeper because of titanium, true.
>Faster because of titanium, false.  Speed is a function of size and power; the
>Alfas achieved great power in a compact size by using a reactor that would be
>deemed unsafe by any rational standard.

Minor disagreement here.  US subs used HY-80 steel, the Alfa reportedly
was 120 KSI Titanium.  Ti has a density of 4.2, Steel has a density of 7.8.
The strength/weight ratios (tens yield KSI/dens) are 10.25 and 28.57
respectively.  For a simple analysis, assuming that strength is purely
a function of the material yield, compression and tension yields are
around the same, and that buckling isn't treated in detail...
The Alfa is able to dive about twice as deep (perhaps a bit less;
rumors unclear) than US 668 SSNs are.  So it still saves around 1/3 of
the relative hull mass over a steel USN sub.  In round numbers,
US Los Angeles subs are 35% hull mass and 35% reactor, so you
save about 12% of gross weight in the hull giving you that much
more to spend on reactor or on other systems.  That assuming the
same reactor tech, that's a 1/3 boost in reactor power, or a speed
increase of something like 10%.

It is true that the Alfa reactor was higher power/weight ratio
than US reactors or even normal Russian reactors, at the expense
of safety and reliability.

>>       If titanium hulls are superior, why do we not produce one?
>
>Because "deeper-diving" is not the sole measure of "superior".  I've yet to
>see anyone make an argument that titanium hulls are inherently "superior" to
>steel hulls.

If price were no object, the weight savings, relative stiffness,
ballistic protection and corrosion resistance would likely make
its use highly common.  In the Real World, price always is very
much a major factor.


-george william herbert
gherbert@crl.com