Uma achega de uma mailling list que subscrevo, parece que as Perry têm a mania de rachar num determinado ponto devido à falta de uma junta de dilatação.
"Couple of points, and replies...
First, the reason why US Navy (and of course, other warships) used aluminum
for superstructures, was top hamper. All those radars and antennas, SRBOCs,
SLQ-32s, and associated masts make for one hell of a metacentric height
problem. Aluminum solved this problem. Yes, it takes less motive power to
move an aluminum ship, and entirely due to weight.
Second, aluminum cannot be welded by any "normal" process to carbon steel.
The actual joint that connects aluminum to steel is a special plate, one
side steel, one side aluminum. They are joined by explosive bonding.
Basically, you take a plate of one, and one of the other, with a very fine
sawtooth grooving in both, and bring them out to the desert. You pour a few
inches of C-4 on the bottom, lay the plates down, and a few more on top.
Toss several layers of sandbags, along with precisely placed detonators.
You move to a safe distance, press the firing key, and voila, you have a
sheet of bi-metallic. Curiously, this joint of dissimilar metals almost
never corrodes, such as is described, and unlike what would be expected if
one did not put a minimum four mils of non-conductive material between the
two metals.
The Perrys seldom have problems with the bi-metallic delaminating. The
problem I discussed earlier is a design flaw, induced by a lack of
expansion joint in the superstructure at Frame 196, or, the approximate
mid-point of the ships long weight distribution. Because of another design
oddity, that does not allow for an expansion joint, the Navy just had to
suck it up, and try various methods to reduce the cracking in this area.
Since I first started working on FFGs in the mid-80s, I haven't seen them
come up with a cure yet.
Lastly, speaking from the deckplates, getting a checkpoint off for steel,
whether it be A-36, DH-36, HTS, STS, or HY-80, is relatively painless
compared to getting the Navy's 146K aluminum checkpoint off<G>. LOTS of
grinding....LOTS"
PS: a referida mailling list é constituída, maioritariamente, pelos jogadores e criadores de uma simulação naval, chamada Harpoon. Vale a pena subscrever mesmo que não joguem o referido jogo, porque há por lá uns cromos muito interessantes, ligados ao meio naval (USN, fabricantes e 'contractors'); a maiorira são americanos, mas tb há uns ingleses, australianos, canadianos e até europeus não anglo-saxónicos.
http://www.teuton.org/mailman/listinfo/hull