I NTRODUCT I ON 



On 12 July 1971, ECHO tower, the easternmost acoustic propagation 

 studies tower of the Azores Fixed Acoustic Range (AFAR) was raised to 

 the surface to repair damage incurred during emplacement and during a one 

 year exposure to the seawater and bottom sediments at a depth of 1500 

 feet near Isia Santa IMaria, Azores, Portugal. 



The Naval Civil Engineering Laboratory (NCEL), Port Hueneme, Califor- 

 nia, in cooperation with the Naval Underwater Systems Center (NUSC), New 

 London Laboratory, New London, Connecticut, participated in the recovery 

 of the tower in response to a request to analyze the deterioration of the 

 tower. Observations of the tower were made at sea immediately after the 

 tower was raised to the surface, at dockside prior to removal of the 

 tower from the sea and, after being raised onto the dock, before and 

 after refurbishment. This report is an analysis of these observations. 



In order to best interpret the condition of structures exposed to 

 seawater at depth, it is desirable to inspect them at depth. This is, 

 in most cases, impractical. If the structure is inspected immediately 

 after being brought to the surface and before its removal from the water 

 its condition wil I closely approximate that at depth. After an extended 

 period at or near the surface or after removal from the sea, the charac- 

 teristics of the structure useful in analyzing its deterioration at 

 depth will change significantly. In this analysis three inspections of 

 the structure were made. The first was made while the structure was in 

 the sea near the surface soon after it was retrieved from depth. The 

 second was made approximately five days after retrieval before the 

 structure was removed from the sea. The third inspection was made after 

 the structure was removed from the sea five days after retrieval. 



Fi rst I nspect ion 



Approximately 12 hours after being retrieved from depth, an - i nspect Ion 

 of the upper portion of the tower was made wh I le the tower was sti I I 

 completely submerged in seawater. A sketch of the tower is shown In 

 Figure I. Depth limitations limited this inspection to the portion of 

 the tower above the center line of the sphere. 



No fouling organisms were found on the upper portion of the sphere. 

 The topcoat of paint on the sphere was lost over approximately 10^ of its 



MBL/WHOI 



0301 OOMDlbT 1 



