so it is necessary to depend on other measures such as the application 

 of copper sulphate solutions, live steam, etc. Such applications and 

 particularly when combined ^^Jith a thorough going follow-up inspection 

 system are very helpful but there is need for more positive means of 

 control of these pests in this type of structure. Marine borer damage 

 can be dangerous on any xvater front structure but it is probable that 

 the maximum danger comes on a structure like a large timber floating 

 drydock virhere the interiors of ballast tanks are not readily accessible 

 for inspection and where the structure is v/orking and heaving practi- 

 cally all the time due to wind, current and wave action and the strains 

 from the handling of ships therein which can be very serious depending 

 on how carefully the dock is handled. Difficulties floiiang from these 

 conditions, as in other msrine structures, sometimes require a reduction 

 in lifting capacity and possibly even taking the dock out of commission. 

 Repairs, when they become necessary, are extremely difficult and expen- 

 sive to make and may be practically impossible without complete re- 

 building. Small wonder, therefore, that there is a decided preference 

 today for steel and also reinforced concrete for floating dry dock 

 construction. Timber still is a pood building r.iaterial for such struc- 

 tures for certain types of 'Tork, hoviever, but unless we can come up 

 with better interior control methods, the tendency will be steadily 

 away from the use of timber. Because of this and the further fact that 

 there are still quite a few Navy-owned timber floating dry docks, con- 

 tinued methods of control are so important. Dry rot and checking give ■ 

 us lots of trouble also in our timber floating dry docks and blocking 

 for both floating and graving docks and marine railways. The first of 

 these is very difficult and costly to correct as it almost occurs in 

 complicated and more or less inaccessible areas and depending on the 

 location where it does occur, it can result, as in the case of m.arine 

 borer action, in restrictions in the use of the dock. So far, replace- 

 ment of the affected timbers is the only remedy available to us in the 

 correction of this trouble. 



Our drydock blocking deterioration problem largely involves checking, 

 and vifhile this may seem trivial, it is actually not. The trouble here 

 has been partially met by binding or strapping the blocks with steel 

 angles or bars, virhich is expensive, and painting the ends of the blocks 

 Tirith heavy paint or coal tar or other bituminous coatings. This check- 

 ing trouble and the general scarcity of suitable blocking materials 

 has forced the Bureau to go to the use of concrete for blocking to a 

 large extent. The Bureau has been experimenting lately with laminated 

 blocking and vdth some signs of success. This problem of blocking 

 deterioration is a serious one in our active docking facilities and 

 in connection with laid-up docks the non-availability of blocking might 

 well be the controlling element in placing such docks back in service 

 in an emergency. It is a cause for serious concern even now on docks 

 being returned to service but if they all had to be recommissioned in 

 a hurry, the problem would be much more acute. Here then are other 

 areas ivhere we need study and help and particular attention is directed 

 to helpin;" the Bureau -..'ith the laminated blocks because something like 



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