Building our trawl in simple steps, with easy supplies!
Our research aims to build previous research done in the Mediterranean. Using the protocols provided by 5 Gyres, the world's premier micro-plastics research NGO, as well as advice from other experts we plan to collect wet and dry micro-plastic samples daily and conduct general plastic surveys of the passages we sail.
Originally, we were hoping to borrow a Manta Trawl from 5Gyres to collect samples, a fancy (and expensive) bit of kit. We would have to ship the trawl from California to Kavala flying out the rest of our equipment with us. Since this meant the environmental impacts and general costs of shipping were pretty high we decided it was best to find another solution. After some discussion and a few helping tips from 5Gyres we decided to build our own!
We engaged with 5 Gyres and used their expertise in building to build our own trawl to match their standards in sampling for micro-plastics. When finished, the entire trawl cost less than £200, would fit in a checked in suitcase and could be taken apart to be stored which was exactly what we needed. If you're thinking of building your own trawl, we highly recommend it, plus it was lots of DIY fun!
What we bought:
- Plankton Net, 300mm diameter / 150micron mesh size -> Cost : £147.50 (this was the most expensive item, and there are other alternatives, but we wanted to match the robustness of the 5 Gyres method)
Everything else was bought from B&Q:
- Plaster mixing bucket (any will do, so long as your net will fit on the end without too much spare space) ~£6
- Plank of wood (approx 1m long), ~£4.50
- Nuts, Bolts & Washers, pack of 10, ~£3
- Pipe insulation (small diameter version, usually used for copper pipes) ~ £1
- Zip ties (we just picked up the longest ones we could find) ~£2
- Duct tape ~£4
- Outdoor wood varnish ~£8
Tools we needed:
- Drill, with drillbits to match the size of your bolts
- Hack saw
- Sturdy surface to work on, and probably a pair of friendly hands to help you hold everything in place
> Our 300mm diameter net slided onto the end of the bucket about 10cm, so we marked out 7cm from the base of the bucket all the way around. (NOTE: if you have your net with you in the work area be very careful it doesn't get caught or snag on anything).
> We then cut away the base of the bucket to leave a 'tube'. We found that the best way for us to get the base off was to cut triangles out of the plastic. We had limited tools so I'm sure there's a quicker way to do it!
> Because the plastic was rough from being cut, we filed down the edges and then covered the entire cut edge with duct tape (as neatly as we could). This was to ensure that the net would get ripped when in use.
> We found that you could pull the net's tow lines around the mouth of the bucket. This could be used as a tow line, but we are going to use it as a back up line to the (very expensive) net.
> When the trawl is fully constructed when we arrive on the boat, the net will also be attached to the bucket by a chain of zip ties that ring around the bucket to keep it tightly fastened to the system.
> Our trawl now had a mouth but it still needed some stabilization. The surface of our bucket had nice ridges at the 0 and 180 degree mark that was perfect for attaching a flat piece of wood to a round surface, although I'm sure with help its more than doable on other buckets. We measured to the centre of the wood and the marked on the four positions we wanted to drill holes for the bolts using a tape measure to make sure they were in symmetrical positions.
> Four holes were drilled into the wood in the correct size for our bolts to fit nicely. The wood was then held in the correct position on the bucket and the drill put through the hole in the wood to drill a new hole in the plastic bucket. We did it this way to make sure they lined up exactly how we wanted them to.
> Holes were also drilled in the 'wings' of wood so a tow line could be attached.
> We then attached it all together using the nuts, bolts and washers. We did it so the head of the bolt was on the inside of the buckets and the nut was on the wood so that the longer ends were not obstructing the mouth of the trawl.
> We then cut the pipe insulation to the correct size for each 'wing' of the wood.
> The took apart the different elements to varnish the wooden plank to protect it against the salt water.
> We the decided to drill holes in the lip of the bucket so we would be able to thread more zip ties from the bucket to the net.
We will post a video of the build soon and more details of the final construction when we arrive!