Just curious if this is physically possible with current ships.
There are ocean going tugs such as the “De Da” and the “Uranus” that are quite capable of towing very large ships fully loaded. I don’t know how big icebergs get, but there are certainly icebergs that are smaller than a large ship. So certainly there are tugs that could tow up to a certain size of iceberg.
According to Wikipedia, your typical iceberg is in the range of 100,000 to 200,000 metric tons. This puts them within the range of the world’s largest ships, which means that the tugs that Princhester mentioned are certainly capable of towing them.
The largest iceberg on record was B-15, which was estimated to be around 3 billion tons. It was basically larger than the island of Jamaica, if you want to put it in perspective. We don’t have a tug capable of towing something that size.
Icebergs aren’t very hydrodynamic, with most of their mass underwater and will have huge amounts of drag a more streamlined ship won’t have and could tip over almost any time, with possibly disasterous consequences for anything attached to it.
And, apart from that, where ever you attach chains or ropes might just break free under the strain. Or saw their way through the berg if you loop anything around the back.
Most of the mass of a loaded ship is underwater also. You are certainly right about the lack of streamlining. It would be a hellava slow tow, probably at only a knot or two. So the slightest adverse current and it would become impossible. Tipping is unlikely to be a disaster. It would just break the towline. No huge deal. Tugs break towlines all the time. The hitch to the iceberg would take a lot of setting up and would have to be multipoint, and would be dangerous to create because of the tipping issue. But the question I guess was whether there are tugs powerful enough, and there are. Never said it would be safe or practical…
Fair enough.
I am by no means an expert in the subject but I found a few aricles that mention that tugboats frequently pull icebergs away from oil platforms in the arctic.
http://www.greenpeace.org.uk/blog/climate/day-icebery-alley-20100824
One problem is that however you attach a tow line to the iceberg, it will gradually either pull loose or work its way through the berg. The reason is that ice is less dense than water so pressure on the ice causes it to melt. Pretty soon, the tow line either pulls out or saws its way through the ice.
There’s no way that iceberg was “only” 3 billion tons, since a billion tons of ice is about 1.1 cubic kilometers (1 cubic kilometer = 1 billion cubic meters, and a density of around 0.9 metric tons per cubic meter); spread out over 11,000 square kilometers, that would be an average thickness of only 0.3 meters - thinner than the sea ice that covers the Arctic Ocean. They almost certainly meant 3 trillion tons, possibly confusion between British and English units (the average thickness of the Ross Ice Shelf, from which it split off, is about 300 meters).
Also, another problem with towing an iceberg is that they aren’t very strong (B-15 has since broken apart into smaller icebergs); if you want to tow it to someplace warm, you would also need to insulate it somehow (although it might melt slowly enough for this not to be a problem, at least if it is big enough). Here is an article that talks about towing icebergs to water-short regions.
So wouldn’t it be more practical then to push from behind? No tow rope to attach, break, etc.
if it rolls you might be smashed.
How feasible is it to encase a berg in a hull-shaped sabot?
That would make the berg more…aquadynamic…thus allowing transport of a berg farther and faster, saving tug fuel.
Also, since a sabot would provide some measure of thermal insulation, allowing a tug to take a berg long-distance to a harbor or port in warmer climes with a fresh water shortage.
Towing it will make it more hydrodynamic, eventually 
I doubt most icebergs would topple easily, since 90% of it is underwater already. It might roll in the water, but wouldn’t topple over on top of you. (This is also a problem for pushing, since you might end up riding up on it rather than bumping it.)
Here’s an interesting bit about icebergs. They can generate a current that, during a dead calm, pulls other things in towards it. It cools the surrounding water. If the surrounding water is warmer than 4’C, the water sinks. The “Captain and Commander” series of novels used this fact for an interesting chapter.
They can also be hazardous critters to get close to when very large, because they can crack with explosive force.
Regarding the 3G tonnes, seems to me that 1 foot depth would be pretty thin and wouldn’t last long. I’ve seen ice nearly that thick broken up and stacked in huge piles by storms in the Great Lakes.