IXD2 outperforming IXB?

First patrol in a IXD2, and I noticed something amis.

As a regular IXB driver I've noted that the accend/decend rate, at 90 RPM (a hair under 2 knots), is 3 meters per minute.
This IXD2 has an accend/decend rate of over 5 meters per minute at the same RPMs and speeed.

Anybody have an idé of how I can correct this for future patrols?

IXB: From 50 meters to 20 meters takes 10 minutes.
IXD2: From 50 meters to 12 meters in 7 minutes?!
VIIB: Slightly faster than the IXB, but nothing near as fast as the IXD2.

More information gathered on the IXD2.

Does not loose any speed while accendind, decending, or turning (even with the rudder at 40 degrees).

Dive time beats a VIIC!
At Ahead Standard the boat dived in 23 seconds.
This was a normal "D" dive, not a "C" crash dive.

At Ahead Slow she dived in 29 seconds.
Both dives were done in rough seas with 15 m/s winds.

No sense to finishing this patrol, as that would be a major cheat.

[Gerald]

I would rather something in between, ICX which fits my needs ............... currently.

[Jimbuna]

I can't say I've noticed this....what game version are you using?

[Gerald]

Originally Posted by jimbuna

I can't say I've noticed this....what game version are you using?

Pardon?

[Jimbuna]

Question was to Snestorm.

Originally Posted by jimbuna

I can't say I've noticed this....what game version are you using?

The "stock" (it's modded) Encore version.
Some small mods, and my own tinkering.

They included alot of modifications. Most are good, but sometimes a soar spot shows up.
They must have unknowingly included somebody's personal super-sub modification.

[Jimbuna]

Originally Posted by Snestorm

The "stock" (it's modded) Encore version.
Some small mods, and my own tinkering.

They included alot of modifications. Most are good, but sometimes a soar spot shows up.
They must have unknowingly included somebody's personal super-sub modification.

That is a possibility I suppose but I've never heard mention of it before