Alfa max depth? - Confused by Polmar's remark

[gerwalk]

Let me return to the

Let me return to the origine of this topic. The comments on my posting by Tom Dougherty made me return to the Cold War Submarines book to search for an explanation on the use of Ti in the Alfas. Polmar mentions these as the reasons (p. 141, hardcover edtion)]http://www.subcommittee.com/forum/icon_cool.gif[/img]

[anonymous]

The Alfa topic is very

The Alfa topic is very interesting. I'm still at a total loss as to why the Russians went to all the enormous trouble & expense to build titanium hull submarines that didn't dive any deeper than US contemporary HY-80 hulls. Although the thickness of the HY-80 hull was once classified, they had a piece of Trepang's hull (SSN-674) on display at the Submarine Force's 100th Birthday at the Smithsonian Institute. I had a pamphlet for the display in my hand and a pen, so I sort of used the pamphlet as a ruler and marked off the thickness of the hull piece with two ink marks along the edge of the pamphlet. (It's roughly a bit over two inches thick, about 5.5 cms). I have no idea what the thickness of the Alfa hull is, but even if you shave a whole 2.5 cms off that figure, it won't give you much in the way of additional hull volume. Jeff’s point about the hulls frames is a possibility. You could either make them smaller or space them out, and this would squeeze out a bit more internal room. Alternatively, I believe he was also suggesting that the hull frames, an integral component of the hull, might not have been as robust as the hull metal, hence limiting diving depth (?) Possible, but again why expend an enormous effort & expense in building the hull and cheap out on the framing?

Make no mistake, the Ti hulls were out there on the edge of metallurgical technology in the late 1960’s when the first Alfa was built. Welding the titanium hull alloy was very difficult, and they built a special airtight construction hull with argon purge above atmospheric pressure to reduce oxygen down to a low level. All workers had to wear breather packs to work on the hulls in these halls. So, given that titanium is very hard to weld and very expensive to mine and refine, why did they bother? One thought I had was that the liquid metal (lead-bismuth) reactor system required heavy shielding and a metal coolant dump tank (as did the liquid sodium reactor in the Seawolf, SSN-575). Liquid metal reactors give a higher power density (and more speed), but the radiation from the liquid metal is much more problematic than that with light water reactors. Increased shielding of components and a dump tank for the liquid metal may have added considerable weight to the submarine, and hence they had a weight margin to make up, and did that with a lighter hull to maintain reserve buoyancy. That would mean that the titanium hull was used solely to compensate for a heavier propulsion system, and the thickness of Ti used (which was dictated by permissible weight margins) supported diving to 300 meters.

The Alfa may have been conceived as a response to American musings in the late 1950’s about 50 knot submarines in a few years, based on the enormous increase in speed seen with the Skipjack class. The Alfa hull is certainly somewhat similar to the Skipjack “body of revolution” design. In any case, the US Navy’s concerns about potential operational depth of a Ti hull submarine like the Alfa led to the modification of the Mk 48 torpedo to the Mk 48 ADCAP, which featured increased depth capabilities.

Tom

[gerwalk]

I think that Tom's idea

I think that Tom's idea on the reactor weight is very interesting and deserves a lot of attention.

The use of liquid metal requires the reactor to be kept running to produce heat in order to avoid "freezing" of the alloy inside the reactor. The soviets even constructed a special dock facility for injecting hot steam to keep the metal in liquid state (IIRC around 150°C or 130°) There was a tender that can provide hot steam to the Alfas too.