How to increse max deep?

[relativy]

Hi i trying to increse u-boot's max deeph.
Historicaly VIIB could dive about 200m, so 210-220 would be optimal
VIIC often dive below 200m. I think 230-240 would be optimal.
One co
In game max i 180m this is defenetly not enough and it annoying me, that U-boot can't dive to 200m.
I found mod that increse this deeph to 200m for each type of u-boots but
VIIC get destoryed at 201m that ridiculous.
Changing max deep in .cfg not work. I know that would be too easy.
Can someone tell me how to fix this max deep?
I don't want also make it too low like 300m. I want in best historically accurate.
I would appreciate it.