I've towed under sail and it works fine if done properly... certainly it can be challenging and requires an experienced person at the helm of each boat, especially if going downwind or upwind.
In this case I am sure you are right, and the size difference would make towing under sail dangerous. A sudden gust enough to accelerate the larger boat to above the smaller boats hull speed could pull the smaller boat underwater quickly.
You would never tow so close that it would become a risk unless manouverering the disabled vessel in close quarters, and then it usually is preferable to tie the vessels alongside each other.
You can see the distances they chose in this particular case in the third image from their Instagram post.
Sail boat towing other boats (similar loa) should attach towing line close to her center of effort. Think like attaching towing line to the mast foot. Not on the stern. Not an easy task to do. That's why many sailors just use any stern cleat.
And the towed boat should attach towing line not to the bow, but also to the center of effort. Then both boats can manouver.
I also lost rudder blade, on the 10m sailboat, in the middle of Adriatic sea, 2005, during regatta, in 35kt NE wind and 3m waves. Not possible to steer anyhow. Tryed to improvize rudder, but we almost lost a crewman. We were on 2nd reef already. SAR came. Since there was no rudder on my boat, attaching towing line to bow was only option. My towed sailboat course was changing +-30 degrees every few minutes, and finally towing line broke loose because of the forestay chaffing.
Yeah and that's further than it looks. I doubt the smaller vessel would have enough line on board to reach that! It's really far. Of course with two boats easy to find enough line.
For commercial vessels like Götheborg they usually bring many hundreds of meters of mooring lines. Easy to get 20-30m runs on several lines when mooring.
yeah makes sense. That is least a few hundred meters!
Unless I were to start using halyards, I probably do not have more than 300' of line on my boat, which is really way more than I need for a smaller boat.
In this case I am sure you are right, and the size difference would make towing under sail dangerous. A sudden gust enough to accelerate the larger boat to above the smaller boats hull speed could pull the smaller boat underwater quickly.