And you've decided to disregard my point on redundancy outright (which is an absolutely crucial metric for a combatant warship, let alone for a fleet-wide air defense DDG at that).
We haven't even touch upon how large and heavy the DEs can get, especially for DEs with higher power outputs, in comparison to GTs. And we do know that hull spaces are a premium commodity on warships - Which is where GTs actually shine in this regard compared to DEs with their significantly higher power density (which leads to much more compact sizes).
I can get 80MW of power with 2x 40MW GTs, or 2x 35MW GTs + 2x 5MW DEs, or 2x 30MW GTs + 2x 10MW DEs, or 2x 30MW DEs + 4x 5MW DEs - And with every one of these options still being more space-saving than your idea of 1x 40MW GT + 4x 10MW DEs. You think stacking higher-power DEs is like stacking Legos or something? And there's still the redundancy and survivability factors to consider, as per the beginning of this post and my prior posts.
Fuel efficiency is NOT the overlord (let alone sole) factor at play when it comes to warship propulsion.
So what's the point?
Let's say you get your GT knocked out and you are left with 40MW in total.
Let's say it uses just 20MW for propulsion vs 20MW for sensors and everything else.
If 40MW allows you to go 30knots as in the case of Type 45 and you lower that to 20MW, you still get to 23.8 knots
Being able to go at 24 knots when you loose a GT seems fine to me.
Even if you lower it to 16 MW, it can still go 22 knots.
If we look at constellation class
,
It got 1 GT of 35MW + 4 3MW diesel engines in CODLAG config. For all the criticism I may have USN, they are very careful in designing warships that deal with contingencies and damage control. They clearly didn't see any problem with using just 1 GT.
As for the argument of too large and heavy.
Let's remember your original point.
1x 40MW gas turbine engine won't be enough for a 9000-10000-ton general purpose DDG. 2x 40MW GTs would be needed
You didn't argue that 1 GT + 4 DEs is not the optimal config from space point of view. (Which btw I think is a fine position)
I certainly would entertain the idea of 2 large GTs + 2 small GTs or 2 large GTs + 2 3-4MW DEs been better configs.
You said it just won't be enough. You have not shown at all that 1 GT + 4 DE can't work.
Consider that Constellation class using 1 GT + 4 DEs in CODLAG config, a 9000t DDG with more powerful GT & larger DEs (accommodated through longer hull) seems entirely reasonable.
Each MTU 9MW engine is 6645x2040x3375mm.
If we just look at the 4.1MW engine at bottom, the dimension is 4690x1600x2336mm.
if you replace 4.1MW engine with a 9MW engine you are only looking at it being 40cm wider and 2m longer.
I see no reason why a 19.5m beam and 160m long destroyer unable to accommodate this.
