I merely did a linear extrapolation based on the following:TheMarcksPlan wrote: ↑06 Jan 2022 20:06I don't quite understand the calculations. From the endurance vs. speed columns I infer you're roughly tracking endurance as correlated to [1 / speed^2]? Horsepower (therefore battery drain) moves roughly with the cube of speed (that's rough because many smaller factors are present such as battery draw efficiency, Reynolds number and therefore friction coefficient, propeller cavitation).
- the measured performance of U 3507 in its final configuration as stated on de.wikipedia.org/wiki/U-Boot-Klasse_XXI
- the fact/assumption that at submerged speed of 6kn a XXI could go 256nm while a XXIX H would go 120nm.
In short: I multiplied the performance (submerged range@speed) of a XXI by the factor 0.469 to arrive at the performance of the XXIX H.
Please use deepL.com to machine translate the German language wikipedia article on Typ XXI. It is very good and comprehensive, because it is mainly based on the books by Eberhard Rössler, the German expert author on Uboats.TheMarcksPlan wrote:I didn't catch this. In the article you linked? I wonder if this really would have worked...kfbr392 wrote:- ability to snorkel at flank speed
You will see that the XXI telescoping snorkel had some serious design flaws. It had too small diameter and was not rigid enough, leading to vibrations at certain snorkel speeds. Plus the periscopes could not be used at underwater speeds of >8kn due to vibrations.
This would not have been the case in XXIX H, which would have used a folding snorkel which stabilized the periscope (a so called "Sehrohrschnorchel" - periscope snorkel). In fact, it probably could have been used very much like a weaving, alternatingly snorkeling and deep-diving Schnellboot to break through the convoy screen at night!
Please read the German wiki page on this issue also.TheMarcksPlan wrote:Your linked article says depth undetermined. It's not necessarily true that circles have greater crush depth - depends on how strongly-built something is.kfbr392 wrote:- greater diving depth (due to circular pressure hull)
The strength of the figure-8 hull of the XXI could not be calculated reliably beforehand and it turned out later that it could not dive deeper than a VII because of that.
True.TheMarcksPlan wrote:What about Caribbean ops? The first T21 was on its way there when the war ended... And South Atlantic, Indian Ocean.kfbr392 wrote:- only one type needed (XXIX H) instead of 2 (XXI and XXIII); massive economies of scale
You might say ignore the peripheral theaters but enables the Allies to concentrate all their ASW in the North Atlantic.
But that is where traffic is concentrated and where the war is won or lost. And successful patrols there mean more Allied tonnage sunk/day/boat.
The boats need to march undetected to north of Ireland, find a convoy, break through the screen, fire the 6 ready torpedoes, disengage, then return to port; use the 4 reloads to target DEs, targets of opportunity, and damaged stragglers. Short patrols of less than 20 days, like in the fall of 1940, close to England. With substantial numbers of XXIX's.
I would argue type XXIX H would have been more effective and survivable than XXI. It could have re-enabled convoy battles in the Western Approaches close to Ireland, an area where uboats have been driven away from since May 1941. According to Rössler, it also featured noise dampening to enable quieter snorkeling, which would have somewhat compensated for its reduced battery capacity.
One XXIX could also shadow an outgoing convoy for days, report its position, evade HUFFDUFF attackers below the surface, and re-enable large scale wolfpack attacks further out in the Atlantic where fewer escorts could be expected.
Additionally, a few XXIX could be sent out further - to Freetown or the US - using older large conventional uboats as milk cows.
But with long patrols, a lot of time is wasted in transit, since these boats (XXI and XXIX) would have marched always submerged at ca. 5-6kn average.
I can see that point also and agree with you that both concepts had their merit.TheMarcksPlan wrote: A final judgment might come down to how much cheaper is the T29 and how many more ships would a T21 kill?
T21's ability to throw out 18 torpedoes in 20 minutes, then evade at higher speed for longer, suggests to me that it might have ~3x the killing power of a T29, which probably will cost at least half as much.
Then again there's other factors (bottlenecks, construction/training time, number of boats at sea and therefore reconnaissance). I'd still probably pick the T21 if given only one choice but I can see the other side of the argument.
The XXIX was conceptualized 15-24 months later than the XXI and thus incorporated some lessons learned from the XXI detailed design and construction.
Also, in parallel to the XXIX, the one-screw Typ XXXI was drawn up in 1944 as a possible successor to the XXI; it had half the number of engines, 75% of the batteries, but still almost the same performance as the XXI. The XXXI too was never built, of course.
This makes it clear that the German officials did not consider the XXI an ideal solution, not even as a boat for long range operations. And definitely not for operations in the North Atlantic.