As an intern on the R/V Oceanus I have had the pleasure of watching experienced marine technicians not only work on deck but also work on cruise planning logistics in the office. On my last internship I never had the ability to see how cruises were actually planned and how marine technicians worked through logistical issues with the science party. What I have witnessed is both amazing and slightly daunting to a new technician. A constant flow of emails with questions and concerns are often waiting for us each morning, and it can be frustrating as you must research whether or not a scientist’s supplied gear will work on your vessel. If the gear the science party wants is not personally supplied then you must look into the different UNOLS equipment pools. Two of the pools I am quickly coming familiar with are NORCOR operated by OSU and the West Coast Winch Pool operated by Scripps. NORCOR primarily offers coring and dredging gear for the UNOLS fleet while the West Coast Winch Pool offers various winches and spoolers.
While planning a cruise a marine technician and chief scientist must assess what sort of winch and wire, if any, are needed for their operations. Currently the Oceanus is outfitted with two small starboard winches (DESH-5 and COM-15 models) and one stern winch (Dynacon HT). Generally there are four standard categories of oceanographic cables, trawl, hydrographic, electro-mechanical/CTD, and fiber optic. Below is a chart of the general characteristics:
Trawl
Hydro
E-M/CTD
Fiber Optic
Size
9/16”
1/4″
.322”
.681”
Construction
3 x 19 galv.
3 x 19 galv.
2 armor galv.
3 armor galv.
R.B.S
32,500 lbs.
6,750 lbs.
11,600 lbs.
46,000 lbs.
Yield
24,375 lbs.
5,063 lbs.
5,000 lbs.
—
2% Yield
28,600 lbs.
5,900 lbs.
—
—
S.W.L
14,300 lbs.
2,950 lbs.
4,500 lbs.
14,000 lbs.
Below are three figures showing the internal slice of the Trawl, E-M, and Fiber Optic wires. I was unable to find a diagram of the 1/4 “ Hydrographic wire.
Trawl wire and hydrographic wire are both generally used on the aft winch as a means of deploying and/or towing various scientific insturments. Trawl wire (9/16″) is used for heavier objects due to it’s size and breaking strength while hydrographic wire (1/4″) is used for smaller applications.
Figure 1. Construction diagram of the 9/16” 3 x 19 Trawl Wire and the 1/4″ 3 x 19 hydrographic wire. All UNOLS 3×19 wire rope are torque balanced, meaning that the rope resists rotation and on the sudden release of the load will not kink or form loops. They also have a higher strength to weight ratio when compared to conventional 6-strand rope.
The .322″ E-M cable is used for various insturments, most commonly a CTD (conductivity, temperature, depth sensor), as its internal electrical conductors, made of copper, allows data transmission to happen between an insturments and its deck box. This allows for functions such as real time variable profiles (exp: CTD display of temperature, salinity, depth) as well as triggering an insutrment to open/close (exp: closing of a niskan bottle on a rosette).
Figure 2. Construction diagram of the .322” Electro-mechanical/CTD cable
The .681″ Fiber optic cable is simialr in a way to the EM cable due to the fact it is also used to trasmit data back and forth from an insturment to a deck box with the exception that it uses thin strands of coated glass fibers instead of copper conductors. To transmit data information is digitized and coded onto light pulses whcih travel along the glass fiber at the speed of light. Once it reaches it’s destination a decoder coverts the information back into a useable format. Due to this process it is much more effiecent then copper conductors. A notable example of its use is in the deployment of ROV’s such as ROV Jason on the WHOI ships. These fiber optic cables allow the ship to send commands to Jason as well as recieve the data and images that the ROV captures.
Figure 3. Construction diagram of the .681” Fiber Optic cable
Currently the R/V Oceanus only has two types of wire on board, the .322” E-M and the 9/16” 3×9 Trawl wire. However both .680 E-M and .681 Fiber optic cables are available if requested.
Breaking Loads
When it comes to working with wire two of the most important considerations to keep in mind are breaking loads and the safe working load. Breaking loads are separated into three categories (definitions are from the UNOLS Appendix A):
-Nominal Breaking Load (NBL): Manufacturer’s minimum published breaking load for a rope or cable.
-Tested Breaking Load (TBL): The actual load required to pull a tension member to destruction as determined by testing.
-Assigned Breaking Load (ABL): Will be the lowest of the Nominal Breaking Load and Tested Breaking Load. In practice, ABL = NBL unless testing shows the TBL < NBL.
The Safe Working Load is the maximum load that is allowed to be supported during normal operation. It is derived from the Able Working load (ABL) and a Factor of Safety (FS), the Factor of Safety is selected by the operator based on rules set by the UNOLS Appendix A. So: SWL = AWL / FS
In order to determine the Test Breaking Load (TBL) of a wire the UNOLS ship is required to send a sample of their wire to the WHOI Wire pool. There they will conduct a tensile test using either fixed ends or one end free to rotate (depending on the requirments of the wire). After the sample wire is broken the ship will recieve a certifiation of testing report showing the breaking features of the wire. Below is an example test certification:
Depending on the results of the break testing and the Factor of Safety selected for the wire, testing could be required every 6 month, annually, or every 2 years.
Overall this has probably been a very technical and in some ways confusing blog post. However this is the nature of the marine technician buisness. Understanding the basic concepts of the tools given to you, as well as the guidelines setforth by the fleet and home institutions (UNOLS Appendix A) can allow you to be a better safer technician. Plus…where’s the fun in all of this stuff if it wasn’t a little confusing? Life would be boring if it was always so straightforward.
Next Post: Understanding Wire and Rope (Part 2) – Rope
