USS ARIZONA MEMORIAL
Submerged Cultural Resources Study:
USS Arizona and Pearl Harbor National Historic Landmark
Chapter IV: Biofouling And Corrosion Study
ARIZONA postscript 2/89
Summary of 1987 and 1988 Annual Inspections of USS ARIZONA
On September 24, 1987, two NOSC divers (biologists) performed two 45-minute dives on the USS ARIZONA. The two took close-up photographs of fouling growth at the 12 tagged vertical photo-biostations. They also measured sediment depths at 20 randomly selected horizontal stations, and made general observations on the status of fouling, sedimentation and corrosion on the ship hull.
Observations indicated no significant changes in fouling, sedimentation or corrosion, as compared to observations made during the July 1986 survey. Mean thickness of sediments measured at the 20 randomly selected stations was about 20 percent less than measurements made at the same 20 stations in 1986. However, the lower recent meanvalue was caused in large part by large decreases in sediment thickness at three shallow stations (No. 29, No. 52 and No. 56), where coarse, loose sediments can be readily moved into irregular mount patterns by wave action. Fish-egg nests that had been observed in abundance on the aft ship deck in the 1986 survey were reduced in abundance by about 70 percent in 1987.
The second annual resurvey was performed by the same two divers in two 45-minute dives on 29 September 1988. Photographic and observational procedures were identical to the previous survey, except that sediment thicknesses were measured at 25 randomly selected stations.
Fouling, sedimentation and corrosion observations again indicated no notable differences as compared to their status in previous surveys. Mean thickness of sediments measured at the 25 stations was 5 percent greater than the mean thickness measured at the same stations in 1986. That increase is within limits of thickness changes that would be expected to occur due to minor seasonal or annual changes in wave action and current motion.
It was noted that most of the horizontal station markers on thick mud sediments had apparently sunk into the mud and disappeared. In the course of future surveys, it would be worthwhile to replace those markers with ones of more stable design (e.g., bases with deep stakes or larger surface areas). Also, it may be necessary to use a new means of displaying station numbers on the markers, because fouling growth was beginning to fill in the engraved numbers, even though they were coated with antifouling paint.
The PVC pipe photo-studs were all relatively clear of fouling. Those had also been coated with antifouling paint, although with a thicker coating than that applied to the horizontal station markers. When visiting those stations, the growth film was gently wiped off with gloved hands.
One area of recently exfoliated hull was observed near the stern of the ship about 30 feet forward of station VS-30. That area measured about 10 feet by 10 feet, and the surrounding metal sheet had about a 1/2-inch gap between it and underlying metal. It was never resolved during the 1986 survey whether these areas are actually "delaminating" or if they are simply patches of outer hull "skin" or thin armor plate that are breaking free. Marine engineers/architects who are knowledgeable on the construction of the USS ARIZONA should be queried on the location, configuration and attachment modes of armor plate and double hull on the ship. Such information would probably be useful in furthering the understanding of exfoliation, which is clearly a major process causing hull decomposition.
Fish-egg nests were seen in very low abundance, and nearly all were on areas of sediment-free, sloping or vertical substrates. No nests had been fanned through sediment to teak deck surface, as was the case in 1986. Abundance of fish nests is likely related to seasonal breeding patterns, and to cyclical changes in overall abundance of fish resident on the ship.
All photographs (slides) taken at the photo-biostations have been retained for comparison with future photo sets to be taken at those stations.
Last Updated: 27-Apr-2001