excerpt from The Venturesome Voyages of Captain Voss;

"An hour later it was blowing a heavy gale, accompanied by a large
breaking sea, and to show my two friends the effects of oil on breaking
seas, I did a little experimenting with different kinds of oil which we
carried for the purpose. Our first experiment was with kerosene . Now,
kerosene, being very thin, takes quite a lot to do any good, but by
using heavy oil , such as fish oil, just a small drop will smooth the
top of a large breaker. It is certainly astonishing to see the effect of
a small drop of oil on large breaking seas. As soon as the oil strikes
the water it will spread itself over quite a large surface, and as soon
as a breaking sea strikes that part, it appears to crawl under the oil,
and loses its breaking top."

Gordon

BTW A few days after this, Sea Queen was rolled in a monster typhoon
and even oil didn't help. The fish oil was spilled in the roll over
making the cabin unlivable!