You could increase the buoyancy by something like 230 kilograms per cubic meter if you fully saturate it on a hot day, but I suppose you'd have to dam up both sides to keep the brine from washing away.

At this scale, even air pressure would be a factor, I'd presume a higher air pressure would be more conducive as large surface area of the water than the ship, though might be wrong.

Would that level of salinity be harmful once it reaches the sea?

Assuming you narrowly dam up the canal near the ship to contain the brine, no I don't think so. Seawater is 3% saline and saturated brine is 26% saline, so you'd probably have sufficient mixing within the canal itself once you open the dams. The canal is 120 miles long and I can't imagine you'd dam up more than a third of a mile at maximum. But it would take a whole hell of a lot of salt.

Yes since the salinity transfer from the canal into the Mediterranean Sea is already enough to make species from the Red Sea colonize the east Mediterranean. The Aswan dam reduced further the amount of freshwater coming to the area. So I would guess adding more salt wouldn’t be too good for the eastern Mediterranean.

And how much salt would you need? At least 100kg per m3. Assuming the canal is 250m wide you need a 400m section dammed and average depth is 15m then you need 150 thousand tonnes of salt. Thankfully Egypt produces more than 3 million tonnes of salt per year so just a few weeks worth of production and enough to fill a large bulk carrier ship.

I was thinking a few lorry loads on the edge they are trying to pull, just to give it a kick briefly so the tugs can get that initial momentum going. More of a brief sudden kick/change to give it that edge.

With that I don't think with the whole damming of aspect would be any better than damming of and pumping water in. Also with that scale you run the risk when you breach the dam of causing what I'd call a saline tsuanmi which might not work well for the ships in it's path and may well cause another to get stuck.

So, more a form of quick kick to aid in getting the tugs an initial bite and a quick dislodge, however small, would only help and may well tip the balance.

> a few lorry loads on the edge they are trying to pull

My intuition is that at the scale of ship, and the canal, “a few lorry loads” is not going to have any noticeable effect.

The ship weighs roughly 100,000 tons. I very large lorry might be five tons. Factor in the static friction of the ship's keel stuck in mud, and the suction opposing any movement.

For kick of initial momentum, I suggest nuclear weapons.

Actually, double that weight. The ship weighs well over 200,000 tons.

wouldn't too much salt damage the ship/make it rust?