Autonomous Buoy project

As part of the NERC Oceans 2025 programme, PML were awarded a capital grant to invest in an array of autonomous buoys. These buoys are designed to be moored at the two major time-series sites of L4 and E1 (see map). The buoy hulls and towers were designed and developed in partnership with locally based Hippo Marine .

Locations	Buoy Design	Floatation test	Work underway

Timeline

Design phase

The contract for the construction of the superstructure was a competitive bid, won by the local firm Hippo Marine. The work commenced during summer 2007 and there were several iterations of the design and specifications. By Christmas 2007, the final design was settled on and the structures themselves were put together. Each buoy is 3.1 m in diameter and is around 7 m freestanding. Once in the water the top of the tower is around 4 m above the surface of the water. One of the distinguishing features of the buoy is the central moon pool: once deployed this fills with water, giving a good location where instruments can be deployed. Instruments are attached to a cage which is winched up and down the moon pool, held in a position around 2.5 m below the surface of the water.

Delivery and floatation test

The buoys were delivered to Millbay docks on a cheerlessly cold February morning (28th Feb 2008). We wanted to see how the buoys behaved in the water (i.e. were they about to sink!) before we paid for them! Once we were happy with the way the design worked (and the cage winched up and down the moon pool) the buoys were then craned back onto the lorry and up to PML for the work to begin in earnest.

Instruments, power, integration

The scaffolders arrived the next day so a platform could be constructed around the two buoys. This was invaluable during the period of integration of the power (wind and solar) and instrument suite. The learning curve was extremely steep having to resolve issues of, for example: radio modem frequencies, possible instrument corrosion (which turned out to be ill founded), AIS systems. The list was endless ... a feel for how the twisting path ran can be found on the blog . The buoys were both kitted out with several Satlantic sensors to determine sea-surface temperature, salinity, water quality, turbidity, nutrients and light together with a standard meteorological station. A web cam has also been mounted on each of the superstructures. The buoys are powered by large capacity rechargeable batteries; these charged by a combination of solar and wind power. The data from the buoys will be telemetered back to the laboratory, via the Rame Head coastguard station , using a combination of UHF radio (for the sea leg) and broadband internet connection. The data will appear on this web site, hopefully by autumn 2008, freely available to the public.

Launch Day	L4 Deployment

Launch and around to Mayflower

Following an early morning interview on the Gordon Spark's show to talk about the buoys on the 12th June 2008, it was off to the lab to await the crane. Both buoys were lifted onto a low-loader and transported (the wrong way down a one-way street) for the short trip to Millbay. The crane was used again to put each buoy into the water and then be towed, one at a time by the MBA Sepia, around to Mayflower. The buoys towed extremely well - but looked vanishingly small once in the water.

Deployment of the L4 buoy

The moorings for the L4 buoy were put in on 26th June 2008 and marked off with a temporary mark. The science behind the two point mooring was quite a feat of engineering: there are two legs each separated into two by a riser. The chain clumps (3 tonnes each) act as a firm anchor. After weeks of waiting for a suitable weather window the first data buoy was attached to its mooring on 22nd July: at least it gave us several weeks of test data at the marina! It was very pleasing to see just how far away we could still spot the structure.

Deployment of the E1 buoy

The E1 buoy was deployed on 7th August 2008 during one of the windiest summers for forty years. Finding a calm period to do this proved problematic. However we were not prepared for what was about to happen ...

L4 buoy in Lagrangian mode

On 10th August 2009, only three days after the successful deployment of the E1 buoy, the L4 buoy was found washed up on Bovisand beach. Fortunately it was found by a colleague at PML and the alarm was raised and rescue ensued. Investigations found that the mooring design was defective and the shackles had quickly undone. Problems were also found with the instrument cage and the instrument packages were lost to the elements. The E1 buoy was recovered, using the SD Salmaid, to avoid a repeat performance on 22nd August 2008.

L4 redeployed

Following an autumn and winter period of redesigning and rethinking everything from mooring design, instrument security to software design, the L4 buoy was redeployed on 16th March 2009 and data immediately started pouring in. Apart from a minor hiccup with the onboard PC hanging, the system proved robust thoughout the spring and summer period.

E1 redeployed

E1 was finally put into position almost a year to the day of its first deployment (5th August 2009). It took around 7 weeks and 3 trips out to the remote position to get the radio-comms right.