I'm an Indian citizen having C1/D US visa working on ship.
Is it possible to get tourist visa and stay for 2 days in London since I will be transiting via London?
It is definitely possible to get a tourist visa for the UK if you meet the criteria.
The status of C1/D visa from the US doesn't aware you an special status in receiving UK tourist visa, you do, however, qualify for transit without concession with a valid US visa but it only refers for air arrival and departure.
So is it possible: Yes. Will you have any preferential treatment because you hold a US visa: Nope.