Secchi Disk Express updated 10-Jun-2013

Build a phytoplankton measuring Secchi Disk in less than 30 minutes of your time!

The disk is for use by Boaters and Sailors with a smart phone who would like to get involved in Plymouth University's global scientific experiment to measure marine phytoplankton (wiki).

Phytoplankton are particularly sensitive to changes in sea surface temperature and so Plymouth University have developed a free Android/iPhone smart phone App to measure seawater cloudiness - and so phytoplankton -with a suitable disk like the one described here.

See Plymouth University's site to get the App and see a map of readings already uploaded. Here's their online interactive Map and if you zoom into Kinsale, Co Cork, Ireland you'll see what I've been uploading using their app and my disk: E.G.


Parts List & possible suppliers (I've not actually used most of them)
An old LP vinyl Record. It has the exact correct diameter of 30cm and even comes with a predrilled hole! Other house hold objects that may also be the correct size/shape include: dinner place mats, pizza plates etc. Of course you can always cut your own disk from wood, plastic etc. I used Felicity Kendal's Shape Up and Dance LP! lp
Stainless steel Eye Bolt or Deck Eye eye bolt
30m or preferably 50m Open reel Tape Measure
100g Lead Weight x2
Stainless Steel Carbine Hook
M8 Nuts x2, M8 Washers, tie wraps, white matt waterproof paint (ceiling paint in my photos works but better to - use outdoor type instead)  


Construction Photos

To construct follow this Photo sequence

Tools: drill & 8mm drill bit, spanner, sandpaper, paint brush.


Other Info & Updates

  • Update 2013.06.09: remove the LP label before paining- it absorbes water and causes the paint to temporarily blister.
  • Alternative weight attachment: photos (I used this method in the end)
  • Using the LP sleeve to protect the disk: photos (with profuse apologies to Felicity Kendal!)
  • To make the disk more robust you could stack one or two more LPs on the first one.
  • I used a 30m tape, so far it's been long enought for use off the cork coast. A 50m tape is recommended though.
  • Tips using the disk from a small boat.
  • Secchi Disk wiki
  • Secchi Disk DIY site for reference only - it's the wrong size/colour for the App:


NB: This site is not part of, connected to, or endorsed by Plymouth University.

Disk construction & photos © Karl Grabe 2013