Regardless of line length the fact you have a underslung load means you have to give it the respect it deserves.
Even with a 200 ft line i have heard of guys getting the line over the back of the skids and have seen empty lines very close to TRs when ferrying an empty line.
I have used a Bambi on a 30 ft line with no problem, the 30 ft bit was chain though and gave the overall load extra weight when there was no water in the bucket.
If not treated with the respect it deserves and the helicopter flown accordingly it will bite.
Actually that's flying full stop isn't it