There’s a whale out there – heave-to and calm the motion down
The first law of getting great shots of anything at all is the simplest – be ready. Your camera should be near to hand, battery charged, memory card clear and with a clean lens on the body. If you can, make a secure place to stow it under the dodger or in a cockpit locker where it’s easy to get at. Failing that, or if the weather is poor, then down below somewhere safe. More great shots are missed because the camera is buried in a locker in its component pieces than through any other factor – I’ve missed more than one shot of a lifetime like this, and I’m far from alone.