Because of these mismatches between vessel supply and demand growth, windows of opportunities develop. Subsequently, dry bulk shipping companies such as DryShips Inc. (DRYS), Diana Shipping Inc. (DSX), Navios Maritime Holdings Inc. (NM), and Safe Bulkers Inc (SB), as well as the Guggenheim Shipping ETF (SEA), are affected by these periods of ups and downs—especially if they’re largely exposed to the spot market.