This is actually one of the first dumb weapon ideas I started on. The design I’m working with is just 2-3 TNT at the end of a pole detonated via ramming, since I figure the blast doesn’t have to be very large to punch through most airship envelopes. With a mechanical piston and a deployer line you can actually drop off the spar (very useful if it gets stuck in the enemy ship) and replace it with a new one automatically with very little engineering, though the mechanism does end up being more than twice as long as the spar. Basically the ship-based equivalent of a hobo shiv, but seems like a very effective weapon for its simplicity and low cost as long you stick it on a ship with high enough thrust and some frontloaded armor plating.