Thanks for the updates.
Why is the Colonial Union building an SD? IIRC the Mintek ones were slower than cruisers and many of the human experiences in war seem to point in the direction of faster fleets to keep or gain strategic initiative.
I don't think they don't have fighters yet, is that correct? (as a side note I predict the lack of fighters and experience using them will cause the humans great pain later on)
After seeing all the pinnaces and cutters that many navys have, are they similar to fighters, and how do they stack up in combat?
The cutters are used by all races for planetary surveys, but that's it. As Andrew said, the pinnaces are very useful for probing warp points to determine what is on the other side. You don't have to risk a full-sized ship, and pinnaces are small enough that they might be able to escaping drawing any attention at all. In terms of combat, as Andrew said, the pinnaces have a point defense unit, so they can defend themselves against fighters, but they can't datalink so fighters, with their six fighter squadrons, will eat them up in combat.
The Colonial Union does not have fighters, and they have not met anyone that is actively using them, so they have no idea that they even exist. And that is the reason the CU is building an SD. You are correct that an SD is slower both tactically and strategically. Most of the active races in my campaign so far have limited themselves to battlecruisers, which are fast, and big enough to do a good amount of damage while carrying enough defenses to make them tough targets. The humans, though, are reacting to their perceived inferior position. They are looking to gain prestige, rather than combat capability, and fielding a force of the biggest ships possible looks like the best way to do that, whether they are combat effective or not.
All things being equal, a force of SD's is difficult for a force of BC's to deal with. It can be done, as the D'Bringi proved in their first major engagement with the Mintek. However, if the SD's are properly designed and deployed, they can successfully take on a mass-equivalent force of battlecruisers, or even a force of BC's that out-masses them, to a certain extent. That is balanced by the BC force's ability to pick the time and place of the engagement, or to decide if there will be an engagement at all.
Of course, all of that assumes the other side doesn't have fighters. The D'Bringi have no interest in SD's because they've been throwing all of their time and money into expanding their fighter corps. Plus, their clans have a raiding mentality, and building large slow battlewagons doesn't really fit into that mindset. The humans are either going to encounter someone who has fighters, or they are going to develop them themselves. Either way, unless they get their asses handed to them, they are going to go with the view that fighters are only good as a support weapon to the large BB's and SD's, because they'll have so much time and effort invested in the big ships that they'll find it difficult to go a different way until their faces are rubbed in the fact that they have to adopt fighters.
Kurt