Why must you NEVER attach a helicopter winch wire to the boat?
Short answer
The helicopter could capsize the vessel if it needs to pull away
If the helicopter needs to make an emergency departure (e.g. engine failure, unexpected gust), it must be able to pull away instantly. If the wire is attached to the boat, it could capsize or drag the vessel.
Quick check
Why must you NEVER attach a helicopter winch wire to the boat?