I heard somewhere that almost 30% of trans oceanic voyages on those colonial era ships resulted in failure. That number seems rather high, is this true? And did a failure mean catastrophic end or simply turning back?

There are Lloyds registers going back that far, providing actuarial information on insurable losses for vessels and cargoes. Prior to that, there are the registers of Dutch joint ventures and the East India Co, and reasonable information of losses recorded by the Spanish and Portuguese during their expansionist stage. The question is a bit broad, as the particular journey and periods of war and piracy affect the data. There were substantial risks associated with particular routes, such as the early spice trade, compensated by great reward, so 30% may not be off the mark there.