What is the collective noun for ropes?

There is no specific collective noun for ropes, in which case, use a collective noun suitable for the situation, for example an array of ropes, reels of ropes, a tangle of ropes, etc.

Some collective nouns for the singular, rope, are a length of rope or a coil of rope.

The noun rope itself is used as a collective noun for a rope of pearls and a rope of onions.