[null and void]

With that much headway a small electromagnetic field is unliely to stop them in the last second or so of the attack. But it's better than nothing.

Agreed. I'd rather be hit by a shark going 20 mph, than hit AND BIT by a shark going 20 mph.

YMMV...

[Citizen Tom Paine]

I wonder how an electromagnetic field is propagated in salt water. Radar waves are quickly attenuated, that is why we use SONAR.

[Mongeaux]

Agreed. I'd rather be hit by a shark going 20 mph, than hit AND BIT by a shark going 20 mph.

It's not foolproof - you could be hit and bit, albeit with less accuracy. The electromagnetic sense provided by the Ampullae of Lorenzini (oil filled pores on the snout) appear to be used to guide the shark to its prey in the last few moments of the bite. A nictating membrane rolls up over the sharks' eyes to protect them, rendering the fish essentially blind at the moment of the bite. However, your chance of surviving the attack are still better with a shark pod than without.