Gun Rocks further exploration and 3D photogrammetry

(July 2016)

By Nic Faulks

The four days of diving on Gun Rocks had been in the planning for some time, and finally it looked as if the weather gods were in a happy mood.

Car on slip

Day one dawned calm and sunny, with Richard Booth, David Lindsay, Simon Smith and Peta Knott (Wessex Archaeology – but in a voluntary capacity) and myself as the participants. We launched the club rhib and all headed out. Finding Gun Rocks at high tide isn’t so easy, but we located and shot the cannon, spot on at the “sticky up one”. That is the cannon which is upended and stands proud of the sea bed.

Cannon on seabed

Day one was all about cutting back the kelp so that we could photograph the cannon without getting moving bits of seaweed in the photographs, which would mess up the photogrammetry. So armed with knives we descended in two waves, to cut back the kelp from the cannon and about 1 metre around each cannon. We all thought that this would be a boring job, but the feeling of slicing through the kelp stipe was in fact quite therapeutic! So much so, David’s agreed bottom time of one hour turned in to 1 hour and 20 minutes….

The second dive for us all was on the St Andre. It is one of those wrecks which can be dived at any state of tide, and especially good when there is a swell as it is sheltered. The visibility was fantastic, everything could be clearly seen including the boilers.

St Andre

After a short second dive so that we could be back in time to catch the slipway open, we headed back to Belford to store the Rhib for the night.

Day two again dawned dry and calm, those weather gods must be happy! With the same crew on board we again headed out to the cannon site. The shot was dropped on to the Sticky up one and we descended down again in two waves. A combination of photographing and kelp cutting was then undertaken.

Diver with cannon

The photogrammetry relies on the photographer being about 50 – 100 cm away from the cannon, taking multiple overlapping photos of the whole surface of the cannon. No flash is used. The software then reverse engineers the photographs to work out the angles to create a three dimensional image. It does however rely on matching photos and textures, so bits of floating kelp are a no no, and when you have cleared so much kelp, it tends to float around. I took about 400 photos, hoping that we could at least image one cannon – we will see.

Day 1 and 2 crew

Day 1 and 2 crew

The second dive was done at the hopper as the swell had again increased as the day wore on. It was also a chance for Richard to show Peta the wildlife of the Farnes, soft coral and seals, which she enjoyed despite being a total rust and wreck lover. The seals were quite playful, often eating Simon’s fins as I tried to take photos of them.

Day three again warm, sunny and calm seas, what had we done right? Today we had a crew change, with Bill Cooper and Tiago Moreira replacing Richard and David. Tiago even brought his suitcase, but we weren’t sure how long he was intending to stay…. Turns out that the huge grey suitcase contains one small camera – who knew?

Crew on RIB

First dive of the day was on Gun Rocks, taking photos of the cleared cannon; Tiago and Nic and with cameras and Simon and Bill with their Go Pros, filming and photographing. Peta was managing the underwater works so she floated around pointing at cannon and ordering us to take photos. We even managed to find the cannon in the gully, returned there after some one who raised it was ordered to return it.

Cannon 2

For the second dive, we were in time to just about get slack on Staple Sound. It is here about 40 metres northwest of Gun Rocks that seven other cannon lie, which remain un–photographed. So Tiago, Peta and I, headed down the shot to find them. The current was running, so we headed with the current to the north…. Then it dawned on us that if we descended with the current, then the cannon were probably to the south and we had missed them, so we finned south against the current. Tiago and I loved this dive, the hydroids were amazing in this tidal environment. Lots of other life too, including plumose anemones, crabs, nudibranchs etc. If we didn’t find the cannon, then two of us had a good dive.

But we did, just as we were tiring, we found the first of the cannon, confirming that the mark in the GPS was correct. From here we found the second and third cannon on the sea bed. All markedly more eroded than those on Gun Rocks. We took some photos then headed back to the surface, as we had a funeral to attend and Tiago had a wet suit to empty.

Changing

Bill Smith a member of Tyneside 114 for much of his adult life, was the inspiration and driving force behind the Gun Rocks exploration. All of the work during the 1970s mapping the site, raising a cannon and researching the wreckage involved Bill. It was only fitting therefore when his son asked current members of Tyneside 114 if they would spread his ashes below the waves over the cannon of Gun Rocks. So, it fell to Simon Smith and Bill Cooper to take the ashes from his family and descend with the urn on to the cannon site. It was a beautiful afternoon, the family aboard Glad Tidings and the divers on the club rhib. Bill’s ashes were released in to the currents, to keep watch over the cannon for eternity.

We all returned to Seahouses, a little pensive over the spreading of the ashes, but all decided that it was a fitting place for Bill to be. We retired to the Bamburgh Inn to raise a pint to Bill, the inspiration behind the Gun Rocks project.

Day four dawned initially sunny. By now we were getting much slicker with sorting out the rhib and getting afloat. One crew change this day, Maurice Daily to replace Bill Cooper. So we all jumped aboard, Tiago still with his suitcase and headed out to the rocks.

Gun Rocks off Inner Farne

Overnight Peta had pulled together some of the photos into a 3D model of the canon. By doing this she was able to see where gaps persisted. So I was sent down with my camera to re photograph a number of the cannon. Tiago and Maurice also did as much photography as they could. Despite removing all of the kelp, large fronds kept floating back in to frame, so these had to be pushed out of the way again. Si and I finished our photographs and headed to the edge of the ledge, sticking our heads out of the kelp over the small wall we could feel the current rushing past. On a flood tide, the rocks of Gun Rocks create an eddy, if you stay within this the water is calm, if you stray beyond the eddy line, you end up rapidly heading for Denmark!

After a short surface interval, Peta made the decision not to do the second dive. My rebreather switched off and wouldn’t turn on and Si decided to just cox the boat and to not dive. So I grabbed Peta’s bubble making kit and joined Maurice ad Tiago for a slack water dive in Staple sound to look for the other cannon.

Cannon 3

Wow, what a dive, slack water, great visibility and found all seven of the cannon. Quite impressive how the cannon sit proud of the relatively flat seabed here, yet they are all so eroded, much more so than the other cannon on Gun Rocks. We took loads of photos to aid in Peta’s photogrammetry quest. This did involve first removing some marine life, pulling dead man’s fingers off the side of the cannon was a horrible feeling, bit like tearing flesh. I don’t want to have to do that again! After 56 minutes we surfaced from our last dive of the week… to rain and stiff breeze.

Once back at Seahouses we again installed ourselves in the Bamburgh Inn to discuss the week and what will become of our research. Peta’s aim is to set up the photogrammetry of each cannon, then have ordnance experts have a look at the results to see if they can identify the origins of the cannon. We know there are Dutch and Swedish cannon there, but are there also English cannon? Was the ship that wrecked simply a recycling venture, returning used broken cannon to a foundry in Sweden? Hopefully our work will yield some results……

Photogrammetry