What about this approach? Put the payload on an inflatable lifeboat. Anchor the boat, and try to get the anchor to land directly on top of the pipeline. Keep tr

What about this approach? Put the payload on an inflatable lifeboat. Anchor the boat, and try to get the anchor to land directly on top of the pipeline. Keep trying until sonar confirms succes. Thread the rope through a loop on the lifeboat. Partially deflate the lifeboat so that it slowly descends. The rope serves as a guide. Use sonar to check whether the charge is acceptably close to the pipeline. Cut the rope and leave. If it was close enough, activate the charge remotely. Otherwise, just leave it there without activating it.