This funny little baseplate ties the entire OpenCTD together. It holds every sensor in a fixed position so that the PVC housing can be flooded with epoxy and sealed against the salty, salty sea. But a lot has to go right to get a good, clean seal. The sensors need to be just far enough away from the walls that the viscosity of the epoxy won't leave a void, but also away from each other. They have to sit just right to let epoxy flow around without allowing for piping up through the baseplate. 

And, most importantly, the 5-minute epoxy for the pressure sensor has to flow below the board. Ideally, the four cutouts will let CTD builders get the nozzle of the epoxy mixer under the board and force the epoxy up into the voids. 

What's funny and frustrating is that almost all of my CTDs work. Something like 15% fail after a few casts and I suspect that it's because of voids in the potting letting seawater into the pressure sensor. That's fine for me, while I'm prototyping. But in a classroom setting, 15% is far, far too high.