Grindrod is a global freight logistics and shipping services company.
The deal will give global entrepreneurs and startups the opportunity to showcase their ideas and deploy innovative solutions.
Despite a $999-million plunge in his net worth, Rupert remains South Africa's richest man and one of Africa's wealthiest billionaires.
Greubel Forsey, which was founded in 2004, manufactures very complicated timepieces.
The billionaire has lost more than $286 million in a single day.
SEACOM is privately funded and about 75-percent African-owned.
Rupert's net worth has dropped by more than $1.8 billion this year.
The double-digit percentage decline in Richemont shares caused Rupert's net worth to fall by more than 10.3 percent.
Rupert's net worth is valued at $11.7 billion, making him the 179th richest man in the world and the second-wealthiest man in Africa.
The move by SEACOM represents a significant step forward in its five-year strategic expansion plans.