The Mayport Naval Station was further stratified by elevation 

 (i.e., by depth). Three elevations were selected to be inspected for 

 each station sampled: 



(1) At the tidal zone near mean low water (MLW) 



(2) At middepth between 15 and 20 feet below MLW 



(3) At or near the mud line 



Based on past experience, it was expected that most of the loss of 

 material, as indicated by thickness measurements, would be at the first 

 zone (MLW) and the least at the mud line. 



Two types of sampling techniques were used during the Mayport Naval 

 Station underwater inspection: random and systematic. The samples for 

 berths C2 East, CI, Bl, and Al used random station number selection. 

 The remaining berths used the systematic approach to select station 

 numbers. A portable battery-operated computer (Tandy 100) was used to 

 generate the station numbers for both the random and systematic selec- 

 tion methods. The length of the facility, the type of selection method, 

 and number of samples desired were entered into the computer. A printed 

 copy of the station numbers for each berth was supplied to the inspection 

 contractor. 



For a simple random station inspection (e.g., Carrier Berth CI), 10 

 random numbers were generated by the portable computer within the range 

 of the length of the facility. These numbers were sorted in ascending 

 order and added to the beginning station number for the particular 

 facility. 



For a systematic station inspection (e.g., Echo Wharf), the length 

 of the facility (1,650 feet) was divided by the number of samples (10), 

 thus providing the skip interval (165 feet) and the range of the first 

 station number. The first station number was determined by generating a 

 random number (137) within the skip interval and adding this to the 

 beginning station number (8583 + 137 = 8720, or station 87+20). Subse- 

 quent station numbers were selected by adding the skip interval to the 

 preceding station number. For example, the second station number was 

 88+85 (8720 + 165 = 8885). 



Three elevations were inspected at each station. Three or more 

 measurements were recorded at each elevation. These measurements were 

 then used to make estimates of the thickness distribution for each 

 facility and determine whether or not additional samples were required 

 for the specified confidence level and desired precision. 



The order of berth inspections was determined by port activities 

 and ship movements. Furthermore, the inspection stations for each berth 

 had to be located and marked. Port plans did not exactly match the 

 as-built facilities. Primarily, this was a problem for the Bravo and 

 Alpha berthing. The station identification of the northwest corner of 

 Bravo, 31+99, could not be confirmed. It was determined that when Bravo 

 was constructed, the cellular construction pushed the berthing wall east- 

 ward about 50 to 75 feet- Station 31+99 was now under the tarmac service 

 area. 



Adjustments to the beginning station number for Bravo and Alpha 

 berths alleviated this problem. All other facilities were referenced 

 from the station numbers listed on the port facility drawings. NCEL 



30 



