I'd love to hear what you guys WANT the harpoon to do. Right now it's kind of... interesting.
My first thoughts is that it needs to not pull you in but maintain range where it doesn't let someone get further away... not just always pull someone in.
I'd like to see, in order of my preference (high to low):
1) the ability to reel in or slacken rope on command (perhaps forward and backward movement keys for that), and as now, the ability to manually release the cable. A ship can never be "pushed" using the tow line, just as a ship can never be "pulled" via ramming.
2) Right now harpoon-forced turning seems unpredictable (though it's hard to gauge with a constantly retracting rope), but controlling enemy facing is generally a far more effective tactic than towing, and intuitively seems like it should be easier to accomplish, even with a large ship-to-ship mass ratio. Ideally, there'd be a noticeable ability to turn a ship when the harpoon pierces the bow or stern of a ship, particularly when the harpoon gun's facing is also perpendicular to the target ship's orientation; effect would be relative to the center of mass, so piercing amidships would have little effect on turning and more ability to tow, as would piercing the fore or aft sections when both attacked ship and angle of attack are parallel in orientation (firing the front of a galleon from the rear of a squid).
3) tow rope does not ever "time out" or automatically snap at a certain distance, but rather the harpoon component gets damaged with stress; any force greater than that of reeling in the line when both ships have engines idling will cause damage, proportional to the excess force; when the component gets destroyed (including by weapons or fire), the cable snaps. Buffing would increase the winch strength (thus reel-in force, and in turn decrease the amount of damage that stress causes). The winch force would ideally be lower than it is now, and perhaps without the harpoon being occupied, the rope would lose all tension until it extends to maximum length; this would mean that, except at maximum range, two crew members would be needed to carry out a sustained harpoon attack (one for repair, and one to just keep the rope from slipping).
4) a noticable effect of relative ship mass on the ability to pull -- a pyra harpooning a galleon can get dragged easily, but when attempting to tow a stationary galleon, acceleration would be extremely low.
5) Enough force in counter-directional force causes the equivalent of ramming damage on any ship to which it applies. Inertia is one such force (so getting yanked to a stop or getting yanked into motion does general damage). Being harpooned by two ships travelling in opposite directions may cause the pulling ships no damage but cause the targeted ship ramming damage.
Some practical effects of the above:
A rear-facing harpoon would be useful on the squid (perhaps the squid's rather large array of engines could counter its low mass, though it could still get yanked around from sudden moves by the target vessel). Such a squid cruising past a galleon at full speed and harpooning in alignment with the center of mass, especially while reeling in, would cause the harpoon to break almost immediately.
A side-harpooning pyra would be useful (particularly from the foreward port-side hardpoint), as that would allow the pyra to reliably orbit a ship while keeping the aft port-side weapon on target. The front tip of a galleon would be a good target for this. This tactic could provide a counter to the typical under-use of the pyra's side-facing weapons (which go completely unused in many games). A somewhat similar, but lesser effect would apply to a harpoon on the galleon's left broadside (since the heavy guns are fore of the center of rotation, while the light hardpoint seems somewhat rear of center).
Spires would be rather difficult to force-turn, since the ship is radially symmetrical; conversely a front-facing harpoon on a spire wouldn't be too useful except when towing closer to blast with a double-carronade -- the harpooned ship would probably have to be directly behind the spire and moving away, before the tension would cause the spire to spin around towards the target.
A squid fleeing a pyra's port weapons could fire their harpoon toward the far aft of the port side while travelling away at full speed. When the harpoon attaches, the initial energy would go into turning the pyra, and if skilled, the gunner could cut the rope just the pyra is facing exactly away, preventing what otherwise would have been a yanking stop for the squid as energy transfers from turning to towing; this would also leave the pyra to continue spinning its angles of fire further away from the squid.
I think all of the above could be achieved without needing to treat the rope itself as a physical object. I imagine that snapping the rope unconditionally by having a third ship cut across it would be immensely more difficult to achieve, so I'm not asking for it