Shortfin Barracuda Bid Maybe Competitive But Still Sketchy

Comments from HK (representing French views) for Submarine Matters' article Shortfin Will th Shortfin Barracuda Design Be Too Heavy = Costly? of August 31, 2015 indicated that the Shortfin Barracuda bid was still subject to considerable change:

HK commented September 1, 2015 at 3:41 PM: 

"Having given it some more thought, Shortfin Barracuda could well displace only ~4,200 tons (surfaced) [565 tons less than the Barracuda SSN figure] .

DCNS are on record saying that Shortfin is smaller than Barracuda. So... the obvious solution is to remove the nuclear reactor module. See [Diagram A] below, from the excellent Navy Recognition website: this ~8m long module (under the deck shelter) is not needed in the SSK. In SMX Ocean it was converted to a VLS launcher (with space to spare - likely for part of the AIP fuel cell/battery modules).

Diagram A - A blurry and difficult to read and understand publicity sketch of Barracuda SSN (Courtesy French Navy on Navy Recognition website). 

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Delete it, and voila! That's ~500m3 saved... or 500t in displacement, as designers typically aim for neutral buoyancy.

This does have the unfortunate consequence of eliminating AIP, however. Also likely to reduce fuel, and therefore range.

As for the rest of the sub, the forward sections up to the deck shelter are likely common to both the SSK and SSN designs. The steam turbine propulsion module in the rear is big enough to accommodate 6 diesels, with space below for more batteries (in pink) and fuel. The electric module (in red) is sized for ~10MW, and probably does not need to be changed much.

If true, this would cut down Shortfin's design and production costs, as well as risk.

HK commented September 2, 2015 at 5:02 AM: 

Regarding Barracuda's power train, the E-motor is directly coupled to the propeller, for acoustic reasons. The reduction gear is only mechanically engaged to shaft and steam turbine at high speeds (likely ~20+kts).

So switching from SSN to SSK is easy: keep the e-motor, eliminate the reduction gear, steam turbine, turbo generators, and associated steam cycle equipment. Replace with 6 diesel generators. These are much more compact and can all fit on one deck. The batteries and fuel tanks go underneath.

Not sure what the thinking will be on whether to keep the 2 back-up 480kw generators currently located amidships [see Diagram B]. Makes sense to replace them with batteries IMHO."

Archimedes commented September 1, 2015 at 10:24 PM:

[along the lines] the TKMS Type 216 is even more risky than Soryu or Shortfin Barracuda as the 216 is definitely a paper submarine compared to the others. 

The Germans may not be as advanced in methanol reformer fuel cell AIP as the French solution. 

CRITIQUES

Concerns about HK's comments above included:

1.  To be compliant with Australia desire for a 4,000 ton (surfaced) submarine - scaling down the Barracuda SSN from 4,765 tons (surfaced) to a 4,200 ton Shortfin will not be easy. Many difficult recalculations of component size, hull thickness, acoustics and buoyancy-balance will need to be made.

1(a).  Space and balance calculations for more batteries and diesel fuel tanks need to be made.

1(b).  As the Shortfin, with its diesel engines, will not be as long as the Barracuda SSN this will alter the length to diameter ratio making the ratio a design problem.

2.  Will the Shortfin be allowed to incorporate the US combat/weapons system - a political and security issue - and will Shortfin include a VLS that can accommodate US made weapons?

3.  The power transfer to submarine's propeller in case of the Barracuda SSN is about 10 MW (or even 2 x 10 MW). That is 3 times the power of the electric motor on the 2,000 ton Type 212/Dolphin-class. Oversized tools or capabilities will not come for free.

3(a).  The Shortfin would need a complete new propulsion system because the whole system has to be reduced to electricity only (with no reactor-steam turbine input). 

4.  How developed is the methanol reformer fuel cell AIP proposed for Shortfin? 
      See DCNS Youtube A below.

Youtube A - DCNS' three air independent technologies to extend fully submerged time/range. 
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Here are two very detailed January 2015 analyses of the second generation methanol reformer – fuel cell AIP that may be being proposed for Shortfin

-  http://www.bakstengineering.com/dfatr-pemfc-the-probable-aip-structure-of-submarine-smx-ocean-concept-part-1-2/  and 

-  http://www.bakstengineering.com/bakst-a-dfatr-sofc-the-supposed-aip-structure-of-submarine-smx-ocean-concept-part-2/

5.  Has DCNS produced a diagram of the Shortfin as good as TKMS' September 2015 diagram of the 216?

Diagram B - This is presumably an early design of the Barracuda SSN with lower weights and smaller dimensions, and a cross tail rather than the more likely X-plane tail.  It is old, in French and difficult to read - hence also "sketchy". However it is still useful. The 2 small diesel engines of 480 kW each are assumed to be retained in the final Barracuda SSN design http://www.sous-mama.org/IMG/BarracudaSite02.jpg :

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Diagram C - Another diagram of the Barracuda SSN. Difficult to understand what is what - sketchy. (Courtesy DCNS via defenceindustrydaily )

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It is interesting how the Barracuda SSN's hull appears very much a scaled down design of the proven Triomphant class SSBN (Courtesy Frederic Petitieuois http://frederic.petitdieulois.perso.sfr.fr/racine/ssbn/ssbn0.jpg at http://frederic.petitdieulois.perso.sfr.fr/page_ssbn.php ). However the Barracuda's sail/fin as depicted in the diagram immediately above varies markedly from the other Barracuda sail depictions further above.

Pete