There were actually three ships by that name and no, none was owned by or named for a Kikuyu man.
The first SS Karanja, a paddle steamer, was built in 1865. The second one was built in 1930 and the third one in 1948. The first ship was most likely scrapped in the early 20th century and there is no seeming link to Kenya.
When the second one was built in 1930, it was one of a pair with another called Kenya. They were both taken by the British Royal Navy during World War 2. SS Kenya (then RMS Kenya) was resold after the war. That SS Karanja now lies somewhere in the depths of the ocean off the coast of Algeria. She was bombed and sunk in 1942 in Operation Torch, the invasion of French North Africa.
This is about the third SS Karanja, launched in 1948 and one of the most important connections between India and Kenya. She was hailed as the pride of the British India Line and served the route for almost three decades. She was a 155m long ship powered by steam turbines twin screw. She weighed 10, 294 tonnes and could carry 60, 180, and 825 passengers in the first, second and third classes respectively on a bi-monthly run.
This SS Karanja normally sailed across the Indian Ocean, carrying passengers from South Asia to Africa and vice versa. She connected Bombay with Kenya, Tanganyika, Zanzibar, Mozambique and South Africa. The steam ship, together with SS Kampala, plied the Indian Ocean for until she was sold in 1976. Traffic between Kenya and India went down in the decade after independence, making the route unprofitable. She was eventually scrapped in 1988.
SS Karanja was an important connection between Kenya, especially in the last years of colonial dominance, and India. Most available evidence is from stories of different Indian communities, such as this person who was born on the ship in 1968 during the 10-day trip. There’s also this story of how apartheid rules affected how passengers interacted and another less controversial story.
Or the model that had belly dancers on deck (see @Blackorwa’s comment below).
But if it wasn’t named after an entrepreneur from Central Province, then who was it named after?
Karanja is in fact an Indian name. There is a city in the Indian state of Maharashtra called Karanja Lad or Karanja, simply. It is named after Saint Karanj and is a holy place for Muslims, Hindus and Jains. Saint Karanj got his name from the Karanj Forest whose etymology is unclear. The village eventually adopted the name of its famous resident, and has been known as Karanja for many centuries.
Its similarity with what is now a common Kikuyu male name seems coincidental. Unless it was inspired by the Indian one.
One Story is good,
till Another is told.