Comment by hwillis

> So that'll cause the tube to break. Glass builds up hige amounts of stresses when it cools down quickly (see prince ruperts drop) so needs an annealing step.

Did you miss that the prestress is the point? There also could still be an annealing step- a continuous oven just like glass fiber manufacturing. Annealing time for prestressed fibers is very short, although I am very skeptical you could actually get something like this to work in practice.

> Moreover changes in temperature mean that using aluminum is probably going to cause the glass to shatter when the temperature changes.

Does temperature change at the bottom of the ocean? I suspect the heat per meter from resistive losses will be very, very low, but it is a missing point.

> Finally that cable is going to be heavy, so unless you make it around the same densisty as salt water, it'll have so much weight it'll snap as soon as you try and dump it into the sea.

That is addressed in the post- balloons to keep the bend angle low as it descends.

> it seems logical to just use PE.

MSC Irina has a deadweight tonnage (cargo+fuel etc) of 240,000 tonnes. PE would be ~15 cm thickness and weigh ~66 tonnes per km, so you'd get somewhere in the region of 3600 km of cable per trip. Atlantic submarine cables are <7200 km, so yeah- it seems very hard to make the case that glass is worth it.

NB: I do not believe that 14 MV cables could be 30 cm in width, but it doesn't matter much. If you make 8 trips instead of 2, it's still hard to justify. Current cable-laying ships are pretty small, despite cables still being decently big- cargo ships are way bigger. Not scaling up the ships would be very silly when they already exist.