Can someone let me know, if there is any thump rule to calculate the reduction on the SWL of cranes onces it is mounted on a barge for doing any lifting activities? Is there any guideline or publications on this? Regards, Pradeep

Unless you are talking of a very small crane on a very large barge, the main constraint will not be the crane capacity but the stability of the barge itself. Putting a weight effectively at the top of the crane jib raises the centre of gravity significantly - this will reduce the GM of the barge dramtically (consider a box on the barge deck, CoG of the box will be about mid-height of the box. As soon as it is lifted, the CoG effectively raises to the highest suspension point). You really need to consider the barges stability imnformation first, then decide if the crane can be used on it.