This is mostly to get a general idea, but I have a specific question. If a ship has a tractor beam, and tows onto a ship, is the towed ship's engines used? IE: Can a starbase have a tractor beam, latch onto a tug, and the tug can pull? I know that a tractor beam can pull an engineless craft, but does it work in reverse?
Now, as for discussion, I'm thinking about a sort of "modular race" where the race's ships are primarily engine platforms with a tractor beam. Using this, the ships will attach mission module and go into battle. Because of this, the race's "ships" could refit frequently to improve engines, but the mission module could be left behind. So, if I upgraded to ion engines, but hadn't upgraded any missile components, then my missile ship could simply decouple and upgrade the engines, then re-grab the missiles and go into battle. This would apply to most everything, and I imagine most designs would look like a "yolk" module that fits over the engine section like a horseshoe, or something.
Some of the more appealing options to me involve detaching the pieces. If needed, an engine chassis could be given a large magazine to supply its attached missile launcher, and if need dictated could detach the missile section and run for it (even though I know the missiles are the more expensive part, I guess part of that is RP value). This runs the risk of war become a game of shuffleboard, with tug ships pushing around stationary pieces, but that could be fun too!
Again, the biggest appeal seems to be separate items for refit, as engines and weapons could be upgraded separately, and therefore cheaper and faster, as well as spreading the load over multiple smaller shipyards. Which is another appeal. If you can't afford to build size 20k yards, you could probably get 10k yards more quickly and produce the engine and weapon part, and hopefully put a ship in the air at half the time and lower tonnage. It'd also help with sensor signal, if I understand it right, as 2 100 HS ships are harder to detect that 1 200 HS. Jump drives would also become easier, at least on a tonnage rating. It would take twice the squadron jump size, but half the engine size, so smaller, cheaper engines can be used instead of hulking capital ships. After all, fitting a 100 HS ship through a jump is much cheaper than a 200. Retreats would also have some tenacity to them. If you know you're going to lose, you can eject the heavy war component and let your engines race away. You're losing your weapons, but if you're losing anyways at least you can save half the ship, right? Additionally, any unused weapon sections could be left idling around a planet and provide some amount of defense.
The disadvantages are there too, though. It would take twice the shipyards, though generally easier to modularize the shipyards. One for engines and three for AMM, ASM, and Sensors. 4 shipyards for 3 ship types, but you could retool any of them if an upgrade was needed. Tractors also have a 1 ship limit, so it would be impossible to grab an AMM and Hangar module for dual effect, which reduces the idea to more of a "half ship" rather than "build your own from parts" of a sort. CIWS would be iffy, because they would protect the engine OR the mission section, but chances are that if you're using CIWS then one of these is disposable while the other is going to need the protection. I could also imagine it being a designing nightmare to get the different blueprints straight, but once you get a system down it should be relatively easy to pick a few parts out of the lot and throw them into battle.
So, thoughts? And don't forget the towing engines question, it probably got lost amongst my ramblings