Regarding the question were there any fins at the taper end I do not remember seeing any evidence that there were any. I had a sly backward glance to see how far the thing extended aft beyond the yachts transom but only remember seeing the red mesh showing the round tapered end. However there may have been fins present but not visible. I was only able to see clearly what was outlined by the red bioluminescent mesh and the bright glow in the water forward. The yachts navigation lights gave a low level of light intensity (port & starboard + stern lights). The object/creature was able to move vertically at a slow and in what appeared to be a a very controlled way so that it lay just under the yacht with the truncated end near the surface beyond the yachts bow and the body hanging down at about 20 degrees to the surface of the sea and projecting beyond the stern. It was keeping pace with the yacht at say 3 knts. I would have thought fins were present required to provide this ammount of control. However I can only relate to the world what I have seen and I did not see any fins. I do not remember it breaking the surface or making contact with the yacht.