Turkey's 214TN "REIS-2" Submarine Project: Special AIP.

Clive Dorer, on December 1, 2021, made interesting comments on Turkey’s Type 214TN "Reis" program (aka "REIS-2"). This is particularly on the Reis class’s tailored PEM Fuel Cell air independent propulsion (AIP) arrangement.

Clive comments:

“I recently stumbled on this interesting Defence Turkey article concerning the Turkish Type 214TN "Reis" program, or more usefully called, as the article explains, "REIS-2"

It has a number of interesting nuggets re construction methods, hull strengths and supply engagement issues (eg: design flaws, pressure hull plates coming from Austria as local industry could not produce HY100 to the required standard).

Also some great insights into the development revisions of the design, with the final design signed off in 2017 being over 2M longer than the original design, and largely detached from the length published in the glossy brochures.

But the bit that grabbed me was that the final design increased the number of the AIP’s metal hydride (MH) (a safer way to store Hydrogen) tanks from 6 x 6 (6 rows of 6 tanks each) to 7 x 6. This is a substantial increase (c. 16%) which PRESUMABLY will extend AIP operational windows.

I say presumably because, although the article isn’t very clear, its implied the liquid Oxygen (LOX) storage is unchanged. This is open to interpretation, but made me wonder if, for example, there are consumption ratios between the two component fuels that change under usage scenarios - EG: does running the AIP’s Fuel Cell Proton-Exchange Membrane (PEM) at very low or very high power output affect the ratio of Hydrogen/O consumption. If so that would inform some interesting speculation on the mission profile [keeping an eye on the Russians, Greeks, Syrians and Israelis?] the Turks envisage for these new boats.

The answer may lie in whether PEM's can be "throttled" intra-cell by varying fuel flow thereto, or if they only really run in binary state (on/off) and the power provision is governed by varying the total number of cells in use. A lot of digging and I've found a lot of contradictory information on this. It seems fuel-cells in general CAN be throttled, but they do have a specific peak-efficiency point, and in the Submarine context of seeking maximum power extraction, the question is left hanging.

On balance I suspect that LOX capacity HAS increased inline with MH, and the author just didnt make this point crystal clear (or didnt know) but the general question of how PEM's are governed/throttle on subs, still stands.

It also begs the question of whether the Turks:

(a) want longer endurance or

(b) need to compensate for hotel load of their indigenous systems. 

Or both. Of course, this we'll never know, nor does it really matter, but fun to speculate.

Finally, it made me wonder if anyone had any idea of the number of tanks in use on the very comparable (in terms of displacement) Singaporean 218SG Invincible-class submarines - which are not yet operational. In other words, is this the extra capacity in the Resi-2 really novel, or not.
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Extra 214TN Reis class Build Details 

from Turkish language Wikipedia