This is the sea trade system from Dragon #6 Ωmega mentioned in my previous post. I've read it before, but, looking back, I have to say I'm impressed. The whole thing fit on one page, was clean, and easy to understand. Kudos to Ronald C. Spencer, Jr. It feels very DIY OSR to me.
I don't think I would use this as is. The minimalist in me wants to at least cut it down to short, medium, and long hauls. But it's cool to see what they thought the probabilities should be. If you can get a hold of a copy, the system also includes simple rules for pilot fees, time spent, and import taxes. Cool stuff.