58 



brushed on to assure adherence to the wood, and the final three coats were 

 sprayed on to supply a uniform finish. It is believed that brushing resulted 

 in better adherence to the wooden hull than dipping in the compound. 



NOTES ON THE USE OF BALSA WOOD AS A FLOAT MATERIAL 



Although the use of balsa wood enabled a comparatively light-weight 

 float to be constructed, the many disadvantages of the material do not recom- 

 mend its use for an efficient load-carrying device. The extreme vulnerabili- 

 ty to damage during launching and retrieving operations complicates the 

 initial waterproofing problem as well as subsequent maintenance. Although 

 the Eclut compound forms a fairly good coating on first application, it does 

 not have adequate adherence properties, so that a small break in the skin 

 aggravates the tendency to peel off as a solid sheet. Furthermore, a small 

 break occurring during the launching operations immediately provides a point 

 where absorption of water by the float can begin. The high porosity of balsa 

 wood then results in early water-logging with subsequent loss in buoyancy and 

 incipient decay. 



Another difficulty lies in maintaining specifications of balsa-wood 

 density among different manufacturers. Samples of balsa submitted for exami- 

 nation showed variations in weight as high as 70 per cent. As a result, it 

 becomes necessary to specify moisture contents and seasoning procedure, which 

 leads to higher costs in manufacture. 



For discussions of the properties of Eclut as well as other water- 

 proofing compounds and materials, References (12) through (20) have been 

 listed. These papers report results of adhesion, breaking, dropping, and 

 fireproof ing tests of various materials. 



PRMC- 3 104-16-8-47- 80 



