How a Trawler Works

I’ve been hesitant to write about the inner workings of the boats I’ve been on because they are, after all, commercial operations and I didn’t want to inadvertently disclose something I shouldn’t. But I’ve been on enough boats now to see that there are common features and I asked on my last boat whether it was ok to post some photos showing hauling which they agreed to. So I can finally show you a bit about how trawlers work.


I’ve got some photos of hauling the net. Setting the net is pretty much exactly the same except everything is in reverse and the cod end (the end of the net where all the fish gathers) is empty. Once the fish is brought on board it is processed – normally headed, tailed and gutted although a few species are filleted.

The net is set at depths ranging from about 100 to 300m. Most of the trawlers I’ve been on have been bottom trawlers which means that the bottom of the net runs along the sea bed while the top floats free. This is my bad (and probably at least slightly inaccurate) illustration of how it looks under water. Please note that among other things this is not to scale!

There’s generally sensors on the net which measure the number of fish entering the net. Some of these fish are able to escape but it’s an indication of how much the net may hold. When the net is thought to be sufficiently full hauling begins.

The warp cable (the big cable that goes from the boat to the trawl doors) is hauled. This can take from 10 to 20 minutes depending on how much cable is set. The warp cables are the two cables in the photo that stretch the length of the deck.

Then the trawl doors are brought up. I don’t really know what these doors but they are really big and come up against the ship with a loud clang. There is a lot of activity as the cable is removed from them so that hauling can continue.

There isn’t much cable beyond the trawl doors and it’s quickly brought on board. By now the start of the net is visible floating in the water.

Because there’s no cable to pull, tactics change when hauling the actual net. Short cables are wrapped around the net and then these are pulled using winches. As each cable reaches the end of the deck another cable is wrapped around the net and the process is repeated. This continues until the cod end is reached.

Then a thicker cable and a stronger winch is used.

Once the entire net is on board all that remains is to empty it. Every boat has fish bins at the stern. These have lids on the trawl deck which open so that the catch can be emptied into them. The bins store the fish and it is removed via a combination of gravity, manpower and conveyor belts to the factory where it is processed.

The net is emptied by lifting it with a pulley and winch so that it is held vertically above the bins. Once it is emptied all that remains is for it to be tidied then set again. And that’s the basics of hauling a trawl net.