The hallway of the Rainbow Warrior, a fabled Greenpeace vessel, was pitch black. I could hear the vague sound of water splashing against the hull, but that's about it. My eyes hadn't adjusted to the darkness, so I was cautiously feeling my way toward the bridge, where Yogi Tujuliarto, the ship's captain, was scanning the night for barges of coal responsible for the destruction of protected coral reef off the coast of Karimunjawa, a tiny archipelago north of Semarang, Central Java.

Yogi was sipping a cup of Columbian coffee and staring at the radar navigation screen. His colleague Lestari, who was also on the late shift that night, had her feet up on the dash. We were slowly sailing through the waters of the Karimunjawa National Park, one of six marine parks in Indonesia. It's waters are full of dozens of species of coral and its forests home to endangered pangolin and Javan deer.

But, for years, coal barges have been dropping anchor off the park's coast, destroying its protected coral reefs in the process, as they sought shelter from high seas and storms. It's barges like these that brought the Rainbow Warrior out to Karimunjawa during its Indonesia tour. I joined the ship's crew three days ago back in Bali, and would spend another three days aboard as we sailed toward North Jakarta's Tanjung Priok port.

Suddenly, a high pitched voice shouting "tango bravo, tango bravo," broke the silence over the radio. "The one from the north is going left. We're coming from the south, go right."

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"Tango bravo," was code for tugboats, the towing vessels that pushed and pulled barges loaded down with coal and oil through Karimunjawa. The islands are close enough to mainland Java that ships heading from Cirebon to Banjarmasin frequently pass by. Yogi jumped to his feet and stared at the navigational system. On it, two blinking dots signified the positions of our ships. We were only five nautical miles apart, but five miles might as well be five million miles when its this dark.