USS ARIZONA MEMORIAL
Submerged Cultural Resources Study:
USS Arizona and Pearl Harbor National Historic Landmark
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Chapter IV: Biofouling And Corrosion Study
(continued)


Biofouling of Vertical Surfaces

Methods

Sixty-one locations on vertical surfaces were tagged for examination and future monitoring. Vertical stations were generally positioned so that 10 vertical "transects" of three stations each were distributed about evenly over port and starboard sides of the ship (Figure 4.1). Most stations were located on the hull surface, but a few were positioned on typical super structure surfaces. Depths of vertical stations varied from 7 to 32 feet.

locations of biofouling stations
Figure 4.1. Locations of vertical surface biofouling stations on the USS ARIZONA. Encircled station numbers denote permanently emplaced PVC studs for photo monitoring.
(click on image for a larger size)

All vertical stations were marked by a 1-foot length of orange survey tape tied to protruding fouling growth. Over a period of several days, it was noted that tape at several locations suffered extensive damage from fish bites. Bites were probably inflicted by balloon fish (Arothron hispidus) that were common around the wreck.

Twelve of the tagged vertical stations were selected as sites for placement of a pair of attachment studs that served as alignment and holding pieces for U-shaped pieces of PVC pipe. Each pipe contained three wire pieces that extended to the fouled hull surface and were used as registration lines for a wire framer on a close-up camera. Each attachment stud consisted of a 6-inch length of 1-inch-diameter PVC pipe glued into a 1-inch PVC flange.

sketch of photo alignment bar
Figure 4.2. Diagram of photo alignment bar.

The base of the attachment stud flange was sanded with coarse sandpaper, and the flange was glued onto the hull or super structure. Splash Zone (trademark name) epoxy was used underwater to attach the studs to the fouling. Initially some studs were glued to shiny hull metal exposed by scraping off overlying fouling and corrosion. However, the epoxy would not bond reliably to the clean metal. Instead we found that the hard, dead fouling surface (where the top layer of soft living fouling had been scraped away) was a much better bonding substrate for the studs, so subsequent attachments were made to hard fouling.

Corrosion and biofouling material, scraped from areas where attachment studs were to be glued, was collected by a diver holding a metal funnel-like device under each area as material was scraped off. That material was funneled into a cloth bag and frozen until later analysis. In the laboratory, scraped material was dried in an oven at 100 degrees Centigrade for about eight hours, until it yielded dry weights of fouling and corrosion components. Most of the corrosion products were separated from biofouling with a bar magnet. Each area scraped measured 6 inches across and 6 inches down (36 inches square).

sketch of bioscraping collector funnel
Figure 4.3. Diagram of bioscraping collector funnel.

Several days after the PVC attachment studs were glued in place, three photos were taken at each photo station using the alignment/registration bar. The area of each photo measured 5.5 inches wide by 3.5 inches high, and the vertical distance between each photo was about 4 inches. Photos were taken with a Nikonos underwater camera, 3:1 close-up extension tube with framer, strobe flash and ASA 64 slide film. Photo slides were later projected onto a screen, and the resultant images were used to identify and estimate the approximate percent-per-area coverage of dominant fouling organisms. Photo station locations are indicated in Figure 4.1 as encircled station numbers.

divers collecting corrosion and biofouling material
Figure 4.4. Corrosion and biofouling material being scraped into collection funnel by divers.
(NPS photo by Larry Murphy)

divers measuring thickness of corrosion and biofouling material
Figure 4.5. Thickness of corrosion and biofouling was measured at selected sampling stations on USS ARIZONA.
(NPS photo by Larry Murphy)

A pair of divers visited all vertical stations and made measurements and observations pertaining to biofouling. To ascertain fouling thickness, a pointed 5/16-inch steel rod was driven through the fouling until solid substrate was encountered. Fouling thicknesses are reported as two values: the first being the thickness of hard/dense, generally dead fouling, and the second being the estimated average maximum thickness of living fouling. Estimates were also made of percent coverage or presence/absence of dominant, easily identified fouling organisms such as vermetid mollusks, oysters, bryosoans, tube worms, sponges, tunicates and algae.


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Last Updated: 27-Apr-2001