It must be related to song "Морячка" (Sailor woman), which has refrain:
А когда на море качка,
И бушует ураган,
Приходи ко мне морячка,
Я тебе любовь отдам.
When sea is rolling
And hurricane storms
Come to me, sailor woman,
I will give you love.
"kachka" is process of swinging and pitching of ship during storm or intense waves. "na more kachka"="there is kachka on the sea" (sea is rolling). It can be associated with movement of the bed during sex.