Page 124 - The ROV Manual - A User Guide for Remotely Operated Vehicles 2nd edition

112 CHAPTER 5 Vehicle Design and Stability
depth. In fact, a well-designed system will have ,1% absorption for 24 h at test depth. Solid syn- tactics are easily machined using the proper tools, feed rates, and speeds. (For an excellent syntactic foam machining guide, contact Engineered Syntactic Systems—www.esyntactic.com.)
Solid syntactic foams have acoustic properties that allow them to be either an absorber or a reflector in seawater, dependent upon the frequencies encountered. Various materials have also been added to the matrix to achieve the desired performance. The benefit is that the performance usually does not change throughout the water column being worked in.
Using solids has drawbacks and benefits. Typically, a solid can be used for full ocean depths while a combination, or macrofoam syntactic (Figure 5.4), has not been generally accepted beyond 10,000 fsw (.3000 msw). This is due to the large spheres used, i.e., 3/8 of an inch (0.95 cm) aver- age diameter. The reasoning behind this is that the larger spheres may have a tendency to implode at great depths, possibly causing a sympathetic implosion on the surrounding spheres, which could lead to a catastrophic failure of the buoyancy system.
FIGURE 5.4
(a)
(b)
Macrofoam (a) and macroballoons (b).
(Courtesy Trelleborg.)