A high underwater speed Type IX

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TheMarcksPlan
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Re: A high underwater speed Type IX

Post by TheMarcksPlan » 17 May 2021 18:59

Tom from Cornwall wrote:
17 May 2021 18:14
TheMarcksPlan wrote:
16 May 2021 06:58
I've cited a much more sophisticated work on the Seraph trials in another thread.

As discussed in that thread, even in 1948-9, RN was not optimistic about killing fast subs:
As usual, someone lauding a piece of work that supports their view on a subject without stopping to consider the intellectual flaws in the trial construction whilst dismissing anything that contradicts their entrenched viewpoint as hopeless. :roll:

Regards

Tom
That'd be a good point if it had the form of a thesis backed up by evidence and analysis. Otherwise there's no difference between this post and the bare statement "TMP is stupid and dishonest," which could be true but needs justification.
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Re: A high underwater speed Type IX

Post by Tom from Cornwall » 17 May 2021 19:25

TheMarcksPlan wrote:
17 May 2021 18:59
That'd be a good point if it had the form of a thesis backed up by evidence and analysis. Otherwise there's no difference between this post and the bare statement "TMP is stupid and dishonest," which could be true but needs justification.
I certainly don't think that is true, but in this case I do think that TMP is perhaps missing the wood for the trees (which is a particularly poor metaphor for anti-U Boat operations I confess!). :lol:

Regards

Tom

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Re: A high underwater speed Type IX

Post by TheMarcksPlan » 17 May 2021 21:34

T. A. Gardner wrote:
16 May 2021 23:24


A reasonable starting point would be looking at the Japanese I 201 class submarines. These are about the same size and displacement as a Type IX C U-boat and possess most of the requisite performance levels this redesign would require.

https://upload.wikimedia.org/wikipedia/ ... ns.svg.png
Thanks.

A next step would be to relate this to T9. What battery volume? What was the historical hull layout and how much could be changed efficiently and quickly to accommodate more batteries?

If hull-lengthening necessary, how efficient/quick on the existing "line?" What drag delta from it?

You'd presumably use existing diesels but what about space for the larger electric engines? Do we have a comparison of T9 vs. T21 electric engine physical volume from which to make an estimate of the intermediate alt-T9 engines?

Interesting question would be whether the quick reload mechanism could fit in this design or any other design. That's a huge amplification of combat value if so.

In general, I agree with the OP comment that Germany made a grave error in devoting little to evolution of Uboats until T21/23. Doenitz was blinkered on quantity and training but in his defense he seems to have been a one-man show envisioning the Uboat Waffe.
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"The whole question of whether we win or lose the war depends on the Russians." - FDR, June 1942

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T. A. Gardner
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Re: A high underwater speed Type IX

Post by T. A. Gardner » 17 May 2021 23:21

TheMarcksPlan wrote:
17 May 2021 21:34
T. A. Gardner wrote:
16 May 2021 23:24


A reasonable starting point would be looking at the Japanese I 201 class submarines. These are about the same size and displacement as a Type IX C U-boat and possess most of the requisite performance levels this redesign would require.

https://upload.wikimedia.org/wikipedia/ ... ns.svg.png
Thanks.

A next step would be to relate this to T9. What battery volume? What was the historical hull layout and how much could be changed efficiently and quickly to accommodate more batteries?

If hull-lengthening necessary, how efficient/quick on the existing "line?" What drag delta from it?

You'd presumably use existing diesels but what about space for the larger electric engines? Do we have a comparison of T9 vs. T21 electric engine physical volume from which to make an estimate of the intermediate alt-T9 engines?

Interesting question would be whether the quick reload mechanism could fit in this design or any other design. That's a huge amplification of combat value if so.

In general, I agree with the OP comment that Germany made a grave error in devoting little to evolution of Uboats until T21/23. Doenitz was blinkered on quantity and training but in his defense he seems to have been a one-man show envisioning the Uboat Waffe.
I would think the starting point would be to clean up the hull to reduce drag and increase speed. This would have to include a new conning tower replacing the current one that incorporated the snorkel.
The diesels don't need to be larger, just the total electric motor output. The diesels drive generators and those drive the electric motors via the battery. The quickest way to do that is get rid of the aft torpedo tubes and the space taking them up. So you upsize the electric motors some along with cleaning up the hull to reduce drag. Recharging the battery takes a bit longer, but that's not a big issue because you do it when snorkeling as well as on the surface.

Image

The deck gun magazine becomes battery space forward and a new section about the same size is inserted aft of the conning tower to increase the aft battery adding maybe ten feet at most to the boat's length. Let's say that gives 25% more battery. This also gives room for the larger electric motors. If you need the diesels to have more power, add supercharging or tweak the performance like was done with aircraft engines. Some redesign of the bow and stern planes would be necessary due to the higher speed as well.

This results in a faster underwater speed boat with less high speed endurance on the battery alone than a Type XXI, but much better than the original Type IX. It also means the boat can travel somewhat faster on snorkel than before.

If you have a boat returning from patrol, you have the conversion materials ready to go and convert the boat during its normal maintenance cycle before returning it to service. You aren't building a whole new boat, just changing things some. Those in production receive the changes as part of production.

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Re: A high underwater speed Type IX

Post by TheMarcksPlan » 11 Jun 2021 17:43

T.A. Gardner wrote: Let's say that gives 25% more battery.
That's not going to be anywhere near sufficient, even with, say, 30% drag reduction.

Those two combined give 79% improvement to energy/drag ratio [ 1.25 / .7 ].

Using a quadratic drag-speed relationship, that allows 34% higher speed for the same time as T9 or 10.3kn - only for the short time that T9 can do 7.7kn.

Using something closer to a cubic relationship (i.e. assuming higher RPM rather than bigger propellers) gives only 9.3kn top speed.

-----------------------

What you'd want to do is use the Type IXD, which extended the pressure hull by 32ft (17%). Except all the extra space would go to batteries.

T9-D was actually longer than T21 (though skinnier); underwater drag would be similar if similarly streamlined (negligible wave drag underwater; total wetted area is the main factor). To accomplish 12kn underwater for the same duration as T21 would require ~half the energy at T21's engine RPM [ (12 / 17.2)^2 ]. Because T9 would use less thrust per propeller, you could probably use lower RPM and therefore greater propulsive efficiency.

In short, a 12kn sub (or faster) based on T9-D seems eminently doable.

This shouldn't be surprising, given what USN achieved with the GUPPY program.

----------------------

Your diagram is of T7, btw, not T9.
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Re: A high underwater speed Type IX

Post by TheMarcksPlan » 11 Jun 2021 18:09

TheMarcksPlan wrote:In short, a 12kn sub (or faster) based on T9-D seems eminently doable.
But what's the combat value by mid-'43?

A 12kn sub is going to be significantly more survivable versus surface escorts. At least quadratically related to its speed, so >2.5x as likely to survive per encounter with escorts. Of course there's greater vulnerability from the sub's larger size and lower maneuverability (latter could perhaps have been addressed in this ATL).

If it has a Schnorkel, it's much less likely to be killed from the air. German uboats in Doenitz's inshore campaign of '44-'45 were at least as safe (per day at sea) as were U-boats during '39-'41. The problem is they were basically manned mines: a ship/convoy had to run them over for them to successfully attack because they were too slow to have much opportunity to position themselves effectively.

The nub is whether 12kn is sufficient to allow the Uboat to sprint into attacking position. They probably could so against 7kn slow convoy. Against a 10kn fast convoy or a faster independent, probably not.

So while a 12kn T9 in, say, 1942 would have presented serious problems for the Wallies (i.e. millions more GRT sunk), I'm not sure that it does in 1944/5.

It gets more interesting if - as is probably the case - the "GUPPY'd" T9 can do ~15kn for an hour. Then it can probably sprint into position against most convoys and would immediately render all existing escorts nearly useless.
https://medium.com/counterfactualww2
"The whole question of whether we win or lose the war depends on the Russians." - FDR, June 1942

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