because of how central engine tech is in aurora, i have always found ship generations occur pretty naturally.
let's say you're sitting on an ion engine fleet and are contemplating magneto's plasma. OK. make a list of the military techs that are higher-priority than the subsequent engine (Internal Fusion I mean, in this example). by higher priority, i mean "more worth the effort than accelerating my timetable for IF engines". Personally, i'd have a reasonable number of 8k techs, and very few 15k ones, in the queue between MP and IF engine projects; i've learned to be fanatical about engines, ymmv.
Once you have that list, you know what your next gen capabilities are going to be, and probably have a good guess what the actual ships will look like. then you ask yourself: what C/P stuff will (net) speed up the delivery of this bolus of bountiful belligerence? you really gotta play this one by ear, since youre spending research time to save shipyard and factory time so it's hugely circumstantial. but, you pays your money, you takes your chances. and now you have a gameplan for a whole ship-generation cycle: the CP research period, the giant exertion of the next engine project, and the follow-up scrabbling to get a tolerable assortment of toys to strap to those cool new engines. as you're laying down those new ship classes, you're maybe eking a last bit of military power out of your labs, the ground forces research and upgrading your missile tech. new ships start coming out of the slips, go find a civilization to ruin, and start the whole beautiful thing over.
eventually there comes a time when having your best two PP scientists using maximum labs on engines and plants doesn't put a critical strain on, well, everything else. at that point generations pretty much go out the window, but in VB6 that was about the time the universe collapsed, so i look forward to dealing with that particular "problem".