Page 80 - The ROV Manual - A User Guide for Remotely Operated Vehicles 2nd edition
P. 80

  68 CHAPTER 3 Design Theory and Standards
mission. The autonomy function is a separate issue from communications. A tethered ROV can be operated in full autonomy mode just as an untethered AUV may be operated in full autonomy mode. The only difference between a fully autonomous ROV and a fully autonomous AUV is gen- erally considered to be the presence/absence of a hard-wire communications link, i.e., a tethered AUV is actually an ROV.
Such design issues will be addressed in Chapter 23.
3.4 Vehicle classifications
Vehicle classification is a hotly debated issue due to the lack of any widely accepted standards on the subject. In the early days of OCROVs, the (rather condescending) moniker “low-cost ROV” drew some rather interesting discussions due to its inference to a child’s toy. Later, as the technol- ogy matured, other lines of demarcation between vehicle classes evolved starting with “hydraulic” and “electric” for the emphasis on drive force for the prime mover (i.e., thruster). Now in the sec- ond decade of the twenty-first century, ROVs range from less than 10 lb (5 kg) for the smallest to multiton hydraulic vehicles topping 250 hp in drive motors. But the classification debate continues.
As the typical client for ROV services generally has limited knowledge of vehicle performance, the larger operators have tended to link vehicle capabilities directly to horsepower. But where is the horsepower measured (even if it is a ridiculous performance metric)?
Many commercial tenders for WCROV services will specify a minimum horsepower rating for the ROV system but will not define the term “horsepower.” For instance, on a recent tender for ROV services an oil company specified a 150 hp minimum rating for a drill support contract. A large electric vehicle was certainly fully capable of fulfilling all of the task requirements speci- fied in the tender. One ROV operator solved the problem very competitively (some would say “aggressively”) by offering a 100 hp vehicle with a 50 hp pump located on the TMS (the TMS is certainly part of the system ...). Voila`—they were awarded the contract! Problem solved. But the naming convention occlusion remains. Expect some standards on this front soon from the oil indus- try standards organizations such as American Petroleum Industry (API) or International Standards Organization (ISO).
In this section, we will examine an older classification example (in this case, the IMCA classifi- cation system). Then we will expand upon the older classification system to better stratify the mod- ern vehicle systems currently available on the open market.
3.4.1 Size classifications of ROVs
As an initial note, the International Maritime Contractors Association (IMCA—http://www.imca-int.
com/) lists its own classification of ROVs as follows:
a. Class I—observation ROVs (small vehicles fitted with camera/lights and sonar only)
b. Class II—observation ROVs with Payload Option (vehicles fitted with two simultaneously
viewable cameras/sonar as standard and capable of handling additional sensors as well as a basic manipulative capability)
 




















































































   78   79   80   81   82