Having printed a red and black version of the more recent buoy design where an o-ring is built into the upper lid of the buoy, I was concerned that the single o-ring in-between the two halves would not be adequate for prolonged ocean use. If the seal were to fail the inside would fill with water and ruin the electronics. Ideally there should be redundancy built into the design for more reliant waterproofing to protect the sensitive electronics.
However, now that I was able to hold the printed parts in my hand and watch it float in the bath tub I was very happy with the size and general shape of the buoy. The small 150mm diameter hull would make for very easy deployment, just throw it like a baseball, while still having a low environmental impact (hopefully!) when monitoring coastal areas or rivers and lakes (as mentioned by a comment by Paul).
So, I wanted to ensure that the electronics would stay dry while still keeping the design simple and easy to fabricate. To meet these criteria I decided to roll back to a previous design idea and include a water tight cylinder (WTC) in the center of the floating buoy. Essentially, all the sensitive electronics will be in a waterproof cylinder that will then be inserted into the core of a buoyant secondary buoy vessel. This has two benefits: first there is plenty of information online about building a WTC and it is tested and reliable method for keeping stuff dry, and second the antennas, lights, and sensors can all be mounted in the end caps of the WTC. The end result is a single electronics canister that can easily be swapped and mounted into anything that floats. So… eventually perhaps that electronics and WTC can become standardized and then inserted into various types or sizes of buoy designs based on the particular need or application.
For example drifting buoys that move with the currents, drouge buoys that sample various data points along the water column, moored buoys that can measure waves for surf forecasting, or simply mounting the WTC (no buoy needed) to a pier for tide monitoring. These are all just ideas at this point, but ideally this could be developed into a more flexible platform that could then be adapted to meet unseen needs.
For this latest reincarnation of a a previous design, the bottom cap to the WTC will function as a twist-lock with the bottom of the buoy. I am hoping to keep the general size of the buoy the same, roughly 150mm diameter and 90mm tall, for now it will be 3D printed out of PLA and then coated in epoxy for waterproofing. The bottom cap will have a built in handle similar to the caps on stainless steel water bottles which will also function as an attachment point for mooring lines or an anchor point. A quarter turn will lock the WTC into to buoy, and the top of the WTC will stick out of the top of buoy which will have the LEDs and antennas built into the cap on the other end. When the battery dies or the data logging is over, simply retrieve the buoy and pull out the WTC. At that point you could install a new battery and download the data form the onboard SD card, or for continued monitoring simple install an entirely new WTC with batteries and use the same buoy hull for continual use. In the future, perhaps the buoy design would be enlarged to 250mm diameter and solar panels could be integrated into the one of the caps on the WTC for prolonged environmental monitoring…but before that I would need a bigger 3D printer!
Here is the first print of the new design using YELLOW PLA, the perfect color for research buoys! The center has a 3.5 inch diameter hole where the WTC cylinder will be installed. This design does not have the twist-lock design yet. More CAD work needs to be done before adding that feature. This is the first time I have used the Printrbot Simple, and it looks like I still need to tweak the settings for the new filament, you can see several cracks or voids where not enough material was deposited. But it printed off of the SD card on the first try, took about 6 hours and the heated bed is great. I highly recommended the heated bed upgrade for large parts like this.