Merging fleets with tugs can be problematic.
Say Fleet A has one or more ships with a tractor beam, and all these ships are tractoring engineless ships.
If Fleet A executes an order to join some Fleet B (which may or may not also have ships with engaged tractor beams), then sometimes (not always) the speed of Fleet B drops to 1km/s.
If I drag Fleet A into Fleet B, same thing happens: sometimes (not always) the speed of Fleet B drops to 1km/s.
The only way to reliably join the fleets without reducing the speed of Fleet B to 1 km/s is to individually drag the tractors from Fleet A to Fleet B in the left hand tree view.
(Dragging this way automatically brings the tractored ships along.)
Obviously, this can be very tedious for large fleets, and can only be done when the fleets are in the same location.
And it means that you just can't use the Join Fleet order when tugging ships.
And I do a *lot* of tugging, so this adds a lot of micromanaging to my playtime.
I'm hoping there's something easy to tweak in the fleet merging logic that can resolve this.
I wonder if the resulting speed is being determined by iterating through the list of all ships, which might be in ascending order of ship construction time, and it doesn't recognize that a ship is tractored unless the tractor has already been processed.
Note: I don't know if the situation only occurs when engineless tractors are targeted, because I only very rarely tractor ships with engines.
Other note: the same thing happens when detaching subfleets with tractors from fleets. Sometimes the newly detached fleet has a speed of 1km/s. Perhaps the same code is handling this as well.