Not the person you're asking, but I sail a 7 ton, 10 metre yacht. I can change course by 90 degrees in under 10 seconds if I need to (probably far less, depends how hard of a crash tack I do).

people do need to sleep if they're soloing offshore, so the warning would need to be at least a minute to be able to wake up, then there's putting on the safety equipment to go out on deck etc. So make that multiple minutes of warning for it to be useful..

Im not aware (which is not to say it doesn't happen) of that many incidents with sailing vessels and whales. However, you've prompted me to look, and it's more than I thought.

https://www.yachtingworld.com/cruising/new-approach-to-reduc...

> Question for you as a sailor in a lighter boat. If alerted, would you be able to change direction fast enough?

That would depend. While under sail (i.e. 99% of the time during ocean crossings), no, not really -- not enough speed and limited heading change options in the prevailing wind. But this is balanced by the fact that, during a typical ocean crossing, I might see another vessel every 20 days or so.

Notwithstanding those facts, I ran my mast-head navigation light, all night, every night, because I was alone on the boat, therefore ... asleep for eight hours every night. If I hit something, it was likely to be something smaller than another boat. Like a waterlogged container or a sleeping whale, both rare but dramatic events.

> Also, I’m guessing at some point the collision is extremely dangerous for the boat not the whale.

Not normally. I've hit whales several times during my time as a sailor. I could tell it was a whale because the boat "thumped" the obstacle instead of loudly banging as with a floating log. I hated the thought of colliding with a whale and did all I could to avoid it, but after dark, such things can't be avoided.

In the case of a big vessel, it's all reversed -- the risk is to the whale, not the ship.