The most severe type of damage to timber waterfront structures is caused 

 by marine boring organisms because this damage often cannot be detected 

 visually until extensive damage has been done. In the United States 

 alone, marine borers and fungi annually cause an estimated $500 million 

 in damage to wooden waterfront structures (Ref 2). 



Marine borers are of two types: crustaceans and mollusks (Figure 1). 

 Of the crustaceans, Limnoria or Woodgribbles are of primary importance. 

 The shrimp-related Limnoria attack and damage wood at the piling surface. 

 These tiny animals average 1/8 to 1/4 inch in length and burrow shallow 

 tunnels which are then eroded away by wave action, exposing new wood to 

 attack. Limnoria eventually narrow the pile diameter usually at the 

 waterline (or the mudline) , resulting in an hourglass shape. 



The molluskan type of marine borers are teredines and pholads. 

 Teredines are commonly referred to as Shipworms and include Teredo and 

 Bankia. Shipworms settle into the wood substrate when they are very 

 young and barely visible. Their clamlike shells begin digging into the 

 wood leaving a pinhole entrance. They burrow inwards and eventually 

 turn to tunnel along the soft wood grain. Teredines can cause severe 

 loss of structural integrity and leave essentially no externally visible 

 signs. The average size of adult Teredo is 1/2 to 1 inch in diameter and 

 1 to 2 feet long. Unlike Limnoria damage, Teredo or Bankia damage usually 

 cannot be detected by visual inspection. 



Pholads or Martesia are approximately 2 inches in length and 1 inch 

 in diameter as adults. Typically, Martesia burrow less than 2-1/2 inches 

 into the piling but leave an entry hole large enough to detect visually. 



MEASUREMENT ACCURACY REQUIREMENTS 



The extent and severity of boring damage, coupled with the large 

 number of wooden waterfront structures, necessitate development of quick 

 and effective timber inspection techniques. These techniques must be 

 capable of evaluating remaining structural strength or remaining cross- 

 sectional area. If the timber pile sustains internal damage, then a 

 parameter other than diameter must be used as an indication of struc- 

 tural condition. 



Inspection data criteria and accuracy requirements were established, 

 based upon structural analyses (see Ref 1). Table 1 lists the accuracy 

 requirements as a function of (1) type of deterioration (internal or 

 external); (2) load capacity of the column; and (3) length of the damaged 

 section (with respect to the total length of the pile) for various degrees 

 of damage. Thus, Table 1 defines the physical and material parameters 

 to be measured and the level of accuracy to which they must be measured. 

 The accuracy is given in terms of coefficient of variation (%) , which, 

 in statistical terms, is the standard deviation divided by the mean. 



With more than one-half the original cross-section remaining, the 

 requirements for accurate measurement are as follows: 



1. For extensive external damage to the piles, 14% (most stringent 

 requirement) 



2. For internal damage from Teredo and Bankia, 20% 



Therefore, the test and evaluation of potential underwater timber inspec- 

 tion techniques were based upon the 14 and 20% accuracy requirements. 



