back in WW2 life jackets had an attached packet of, according to the official label, what was called "life jacket repellent". Which may be a hint as to its effectiveness in repelling sharks. It was, as I remember, a mix of a ferric sulphate and a dye that produced a dense cloud that was intended to provide a visual barrier. Testing showed that sharks freely swam into and through the cloud of dissolved repellent. Evidently the sulphate wasn't sufficiently distasteful to sharks and they don't mind swimming into water they can't see through.

Might have something to do with sharks primarily hunting by smell and, in part, by sensing electrical fields closer in.

The repellent was not tested for its ability to keep life jackets away. One has to assume, with typical governmental literalism and humor, the wording of the label wasn't any accident.

Bottom line is when you abandon ship you either retreat into a boat or you take your chances. The good news is that most shark encounters are not hostile.

Aerial observation of surf lines shows that among the lines of surfers are sharks. Often large ones. And yet attacks on surfers are few and far between. Lots of surfers have tales of being rubbed up against or 'sniffed'. But he number of actual attacks are small. The speculation is that sharks generally only tend to bite surfers when the humans kick them or land on them or when the sharks are feeding on fish in disturbed water and the humans put themselves in the middle.

This accounts for the attacks tending to be a quick nip, possibly an expression of annoyance for being kicked, or a quick bite, often just a taste, followed by release. More exploratory than feeding behavior.

If and when you have to abandon ship the biggest dangers will be drowning and hypothermia. Sharks, if they make the list at all, are pretty far down on the list.