The correct answer is D) adjust the towline so the tug is on the crest when the tow is in the trough. This is correct because in heavy weather with a large ocean tow, you want to avoid having the tug on the crest of the wave when the tow is in the trough. This can create excessive strain on the towline and increase the risk of parting the line. Instead, you want to adjust the towline length so the tug is on the crest when the tow is in the trough, which helps reduce the dynamic loading on the towline. The other options are incorrect because: A) a long towing hawser can increase the risk of parting the line in heavy weather, B) keeping the low point of the catenary in the water is generally recommended, and C) keeping the stern of the tug well down in the water can help with stability but does not address the critical wave motion issue.