Chapter III: Archeological Record

USS ARIZONA

Methodology

The approach used to document the USS ARIZONA and its immediate environment was low-tech and labor-intensive. No one had ever attempted a detailed mapping of a 608-foot battleship in water of 6-foot visibility. There were no guidelines to follow and no black-box technology that could significantly help. Photogrammetry was precluded because of the visibility constraints, shallow water and high site relief. High-resolution sonar mapping techniques are still in the early stages of development.

The most valuable assets at the disposal of the research director were a highly experienced team of NPS survey archeologists and illustrators, and other diving personnel from the park and US Navy. The methodology centered around string, clothespins, measuring tapes and a lot of mapping savvy -- ironically, much of that derived from mapping Pueblo Indian sites in the desert. About half a mile of No. 18 nylon string was laid over the ship to establish straight lines in a world of twisted metal. Lines were marked every 10 feet with numbered plastic clips, forming a kind of "cat's cradle" over the site. The cradle with its measurable lines was first plotted on paper and then, laboriously, the shipwreck measurements followed. Simple trilateration techniques related known points on the marked lines to target features on the wreck.

Figure 3.1. U.S. Navy divers add marked clips every 10 feet to survey line on USS ARIZONA after it was installed by NPS underwater archeologists. (NPS photo by Larry Murphy)

Each evening all the data acquired during the day were copied onto a master set of drawings. Each morning mylar overlays were made of small sections of the drawing and affixed to divers' slates, who returned to the bottom for additional detail. Divers had a list of required measurements, and they would simply fill in the blanks on each dive. On some dives more than 60 measurements were taken by a two-person team. Thousands of separate measurements were taken during the four weeks spent in the field. An ordinary plastic protractor was used to record changes in angles of the straight lines.

Responsibility for the planimetric view was given to Jerry Livingston and the elevations (profiles) to Larry Nordby. Farley Watanabe and Mark Senning were assigned to the starboard elevation, while Larry concentrated his own in-water time on the port elevation.

To confirm accuracy of critical points along the gunnel and other features of the badly deformed deck, a local survey crew shot targets with an infrared theodolite, or electronic distance-measuring (EDM) instrument. Divers held the reflective mirrors of the EDM motionless on top of a PVC pole, as the bottom was held in place on the feature to be mapped. This proved to be useful in areas where the pole could be stabilized, but was awkward at other points.

Figure 3.2. Numbered clothespins in upper right hand corner marks a survey point. Diver is sketching feature for inclusion in site map. (NPS photo by Larry Murphy)

A particularly vexing problem developed over the first few days, when the string baseline calculations on the planimetric view repeatedly indicated the gunnels to be several feet wider apart in the bow than was described in the construction plans. This beam measurement was not a detail that should have been altered on ship modifications. We hoped that the infrared theodolite would correct the disparity. To our surprise, the theodolite confirmed the data gleaned from the strings, indicating the ship had expanded at the explosion point, much like an overpressurized tin can. This buckling had not been evident to the divers underwater, whose visual references were compromised by the visibility.

The hull curvature presented other problems for the elevation views. A diver even one body length away could not see the ship, so it was necessary to hand-measure over curves as if they were on a two-dimensional plane. For our purposes, the ship was divided into 10 sections of 60 feet long by the vertical strings from the cradle, creating 20 individual "frames" to be drawn in two dimensions. This approach had one problem: When the whole vessel was pieced together, the scaled drawing was longer than the actual ship. Consequently, the illustrators had to correct each frame to compensate for the two-dimensional depiction of the ship's curved hull. This correcting process was more pronounced on some frames than others, depending on the curvature of each specific section of hull. This was a point in the project where it was highly advantageous to have mappers experienced in rendering cliff dwellings on Southwestern archeological sites. The irregular, three-dimensional features nestled in curving alcove walls of sandstone cliffs provide similar problems for illustrators.

Figure 3.3. After being drawn, each feature is measured back to two points on the baseline. This allows accurate mapping through a simple geometric procedure called trilateration. (NPS photo by Larry Murphy)

By the time the assessment project began in 1983, low-cost and self-contained color video systems had become commercially available. One of these units was purchased and put to great use in these field operations. The video was capable of recording at least as much as a diver could see in the limited visibility, and was much easier to use in the harbor environment than standard photographic systems. Still photography does not provide instant feed back to the photographer, whereas the color video had a monitor built into the housing that permitted the operator to see exactly what was coming back in "real time." Tricky photographic problems associated with using artificial light in silty water were also reduced by the supplemental use of video.

Perhaps the greatest advantage of video became apparent in the office in Santa Fe months after the field work was completed. Livingston was able to fill in much detail between known map points on specific features by consulting the video tapes. Besides the assistance this provided in the mapping process, tapes resulting from the survey activities proved to be exceptional tools for education, both at the visitors center and on loan to the electronic media. During the active phase of the project, all Honolulu TV channels carried several minutes of the video returns every night for weeks running, and some segments were broadcast on national television.

In addition to rendering architectural drawings of the hull, the team conducted perimeter searches of the battleship to establish the site's extent, inventory the recognizable artifacts where they lay in the wreckage, and mark their positions on the site's base map. The depth of silt around the perimeter of the site was determined by probing with a PVC rod marked in 1-foot increments. All artifacts were left in place, with the exception of items that presented an unacceptable hazard to the memorial that straddles the ARIZONA and through which 5,000 visitors pass each day. Hazardous material included unexploded shells from the 5-inch guns, sacks of congealed gun powder, and corroded high-pressure air or acetylene bottles that were probably used during the salvage activity. The Navy's Explosive Ordnance Disposal (EOD No. 1) team was stationed nearby, and on several occasions they responded to our request to remove such items while the surveyors gingerly exited the water.

Additional studies of the wreck's natural environment were carried out with much greater intensity in 1986, and the methodology is reported in detail in Chapter IV. Those studies included a detailed analysis of the biomass and corrosive properties of the ship, in addition to silt measurements. The technology included manual probes, sampling containers, oxygen probes and a bathycorrometer, which measures galvanic potential of the metal underneath the biofouling crust.

Perimeter surveys to determine the extent of the wreckage field were accomplished using two modes: side-scan technology and divers. Side-scan sonar passes were run in 1983 and again in 1988 using a Klein 100 KHz. A Mesotech side-scan unit used in sector-scan and polar-scan modes was added in 1988. To augment sonar results, dive teams were deployed to conduct 180-degree sweeps that covered the bottom at least 100 feet from the hull remains. The only items divers found were features already noted by the sonar. These features have been incorporated into the site map.

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