How about this instead:
Dual Heavy Harpoon. Fires two shots, one after the other. Rather than the cable being attached to the gun, it is attached between the two heavy harpoons.
Usage: Fire first harpoon at one enemy (or friendly?) ship, then target and fire the second harpoon on another ship. It ties the two ships together.
You could even shoot it into two of your own ships, and then 'clothesline' the enemy ships by flying either side (although that sounds like it might be awkward to pull off, and I'm not sure what the benefit would be of doing it.. I should have thought that idea through a bit better really >.< )!
One worry I would have about being able to shoot your own ships as well is that it would be too open to trolling.. it wouldn't take much for one rogue crew member to mess with your whole team.
Still, I kind of like the idea of attaching enemy ships together.. it could be funny if the line shortens in length once both ships are harpooned, pulling them close together and making it difficult for them to steer. Especially if they happen to be facing opposite directions at the time! xD
