What do you want to calculate?
If I understood you right, you want to calculate with water and air, therefore you will need FlowSimulation. If you want to do this, you have to split up your calculation. I'd say it is possible to calculate the body which is in the water with FlowSim and then export the forces of the water to SWX Sim and calculate stresses or so (faces need to be split up and the computational domain of FlowSim must be also adaptable)
Thanks for your input. I will try the same.
J K Mohapatra