To be traveling together side by side (as two boats in the sea, two planes in the sky, two jeeps on a road, two people walking side by side.
When N- is used sometimes an -an suffix is added when mentioning the object one is going to travel alongside.
I should travel alongside his boat because his engine keeps dying.
The reason we weren't afraid of pirates is because a ship traveled alongside us.
When we went to Palawan our boats traveled side by side.
A pumpboat came alongside our launch to look for an opportunity to rob us.