I am quite skeptical on the numbers circulating on shipping and tourism contribution to Greek GDP. These number are numbers by their respective lobbies so they tend to be inflated (for example, by including a broad area of services to "tourism"). They both use these data to extract tax concessions from the governments.  I would be happy to ask shipping and tourism lobbies to give figures not only for their supposed contribution to GDP but also to tax revenues (har, har). Their tax concessions on one hand and subsidies they get on the other one are really outrageous.

With a quick look at the official site of Hellenic Statistics I couldn't find data on Greek GDP composition braking down to shipping or tourism. That's why figures quoted by various sources differ significantly. For example, a recent paper by National Bank of Greece quotes shipping as 6.9% of GDP.

"Eurozone leaders have turned a €50bn Greek solvency problem into a €1,000bn existential crisis for the European Union." David Miliband