UB88 Orthomosaic + 14 Year Retrospective

Background

The UB88 team first located and dove the UB88 sub in 2003. They did multiple dives on the wreck and produced both still pictures and videos.

At some point, Gary Fabian took frames from the videos shot by John Walker and created a photo mosaic of the wreck:

I’ve referred to this photo mosaic many times and I have used it as a reference for my numerous dives on the sub.

After my recent post about the completion of a photogrammetry model, I had more than a few comments from friends about comparing the wreck from 2003-2007 to what it looks like today. It sounded like a great idea…

After I had done my initial penetration dive and shot some hi-definition video, I had a few emails with Jeffrey Delsescaux who is an Associate State Archaeologist with the Office of Historic Preservation in California. He authored the article “California’s Aquatic Assassin” about the UB88 back in 2019.

Based upon the video I took inside the UB88, we had multiple discussions about the debated topic of whether or not there are/were explosives in the hull (we both now believe that there are NOT explosives inside).

As part of the above mentioned publication on the UB88, Jeffrey had produced a photogrammetry model (I believe it was based upon the video shot during 2004 on those original dives):

One of the things that Jeffrey noted was that the original video footage never went past the front of the sub to the area where there is some debris which is included in the model I produced (more on that in a bit).

Sony Camera “Live View” Sidebar

At the end of my most recent dive to finish the stern section of the UB88 (which was a failure), I had some “extra time” and decided to use that time to take some natural light photos of the UB88 in an attempt to recreate the original photo mosaic.

It was another failure, but I learned a few things. I had read about a “feature” of Sony cameras called “Live View.” Well, that was my downfall. I was snapping away and taking pictures but the camera was having a little bit of a hard time focussing but I kept going. The pictures on the LCD on the camera looked okay. I had the “Live View” feature set to “off” and so what I was seeing was the camera jacking up the exposure in order to focus but it wasn’t what was actually being used for the exposure.

When I got back home, I dowloaded the pictures into Lightroom and saw this:

Well, that looks like absolutely nothing. I had underexposed the photo by at least 2-3 stops. Here is that same photo after adding 2.25 stops of exposure:

Building a Photomosaic

I proceeded to over-expose all my photos in Lightroom (which resulted in a lot of “noise”) and then tried to build a photogrammetry model in Metashape hoping to get something close to the original. Unfortunately, due to the grain and other issues such as a LOT of fish near the bow, I was unable to build a model.

After a few emails with Jeffrey, he had mentioned that Metashape allows you to create a very high definition photo mosaic so I decided to do some investigation. The “regular” version of Metashape doesn’t have the option to build a photo mosaic; however, the Pro version does have this option so I spent some time investigating it.

I ended up building a 2D mosaic and used the option to build it based upon the current position and aspect of the 3D model. The results were pretty impressive. Below is a screen capture of the mosaic:

The mosaic took about 90 minutes to generate and the file size is 36GB for the default size / pixels per inch. It is 76,545 x 14,825 pixels so you can zoom in almost infinitely. You can see Drew Wilson on the port side by the bow torpedo tubes. That is somewhat imperfect due to Drew moving around while I was taking pictures, but it does give a good sense of scale.

DroneLab Links

I have uploaded the orthomoasaic to dronelab.io so that people can inspect it (thanks to Kevin Bond for the suggestion). Unfortunately, Dronelab doesn’t do well with “long, skinny” orhtomosaics so I need to split it into four “square” chunks. Below are pictures of the chunks and links to the models.

The Effects of Time

There are a few areas of the wreck that have definitely seen the effects of time. It is really hard to judge whether these changes are just due to erosion or whether they are from divers going to see the UB88 and damaging the structure with anchors and/or dowlines.

Bow Torpedo Tubes

Obviously, the impact of time (and possibly of people using anchors, etc) are most visible in this area. The four forward torpedo tubes are completely visible now whereas they used to be covered by the outer hull (except for a small area where you could “peak” a view of the tubes when they first found it).

Once again, notice how Drew is somewhat obfuscated here due to the “mosaic” effect of taking multiple pictures shot at different times with slightly different compositions.

Exit Hole Area

The exit hole looks about the same; however, you can see that the area where the shell entered the outer hull has been collapsed and you can see the inner structure.

Here is a closeup:

Stern

This change was not as obvious when reviewing the Fabian mosaic; however, when looking at the mosaic produced by Jeffrey Delsescaux, you can clearly see how a part of the outer pressure hull has either been eroded or damaged due to anchors. Here are three screen captures of the same area:

This is an area where you can really see the shape of both the external and internal hull shape. This is because the port side is somewhat intact and the starboard side has collapsed.

Conning Tower

Just forward of the conning tower on the port side, you can see there has also been some additional damage. The area on the starboard side hull looks about the same in both models. However, the outer hull on the newer model shows that there has been some damage or erosion of the outer hull between the conning tower and the gun mount.

Conclusion

We will never know how much of the damage is caused by mother nature and time in saltwater vs. downlines and anchors from divers. What is most amazing to me is how intact the UB88 actually still is. It passed 100 years underwater in January of 2021. For being underwater in some pretty harsh conditions for 100 years, she looks amazing and I will never tire of diving this site.