In the nautical world a “long tow” is a tug boat pulling a barge on a long cable.  When they are towing in the ocean the cable can sometimes be REALLY long.  It is a way of shipping anything that can be loaded on a barge in quantities that are smaller than would justify the use of a full sized containership.  Long tows are used around the world, but here in Hawaii they are a large fraction of the shipping you encounter on the ocean. They are used for almost all inter-island transport, and a large fraction of the goods shipped from the mainland arrives on barges like this.

They can be real trouble if you are not paying attention.  Here’s why:

You are out sailing on the ocean, and you see a tugboat in the distance…

You look around to see if there is anything attached.

I don’t see anything…  do you?  Let’s look a bit further…

Nope.  Still nothing.  Maybe look just a bit further…

Oh!  Look at that!  Yes it is a barge.  And yes, it is attached to that tugboat in front with a very long cable.  When I checked on my radar, this tug and tow combination was over a half mile long.  If you tried to go between them, you would have a VERY bad day.  At night the situation is even worse, although the barges are lit, the lights are typically quite small and non-obvious.

Why are they so far behind?  One reason is the barge does not have any kind of brakes.  If the tugboat’s engine was to stop and the barge was towed close behind, the tug would be run over by something an order of magnitude or two bigger and heavier.  Not a pretty picture.