A big oil tanker will take a long time to stop and its easier for others to pull you out of the water from a small boat
All merchant vessels are equipped with a rescue craft - that said a member of the crew needs to observe that you have ditched.
Also don't forget flairs its very hard to see someone in the seas and a locator
Or one of these may be far better:-
Laser Flares
This is also useful for forecast sea states (swell, period, surface wind) - you can even work out a good theoretical ditching heading before departure:-
Sea state
Or if you don't like the look of the swell cancel and go another day.