Designing a Lanyard to Retain Scupper Plugs
At Pivot Point, our team engages in continuous innovation to improve our customers' products, and make their manufacturing processes faster, better, more efficient. If you have a fastening challenge, we take pride in providing the right solution. From fasteners to tethering solutions, rings, pins, cotters and hooks, we have everything you need to meet your fastening challenges.
Our clients in the marine industry operate under uniquely challenging circumstances. The solutions we provide to them must meet their tough operating environments. Here is a great example.
- Industry: Marine
- Processes: Using a lanyard to tether scupper plugs on ships
- Company Background: A long-time manufacturer of marine equipment including cargo gauging, overfill protection solutions, venting, barge connection and other marine products.
- Challenge: Design a lanyard that is strong, yet flexible enough to allow secure tethering of scupper plugs that prevent overflow of oily and contaminated water onto a ship’s deck during bunkering.
- Assessment: The deck of a ship presents unique challenges in terms of corrosion by both saltwater, and chemicals. The nature of a scupper plug requires unique eyelet configurations to allow for seamless tethering and robust life-span.
Optimizing the design for a lanyard to tether scupper plugs
In this case study, we’ll focus on a lanyard used to tether “scupper plugs”. A few facts to help you understand the need and role of this product:
- Scuppers are an opening cut through the bulwarks of a ship so that water present on deck may flow overboard.
- Scupper plugs are inserted into the scuppers during bunkering, which is the process of receiving oil in the ship’s tank, as well as during other cargo operations.
- This is to prevent oily, or otherwise contaminated, water from flowing overboard into waterways.
- Scupper plugs are required by law for 400’, or longer, oil tankers and offshore oil barges in case of oil spills on deck.
Important considerations for selecting key characteristics
While the lanyard used to tether this scupper plug may seem straightforward, the characteristics were carefully chosen for the application. 1/16” cable was chosen in order to provide a good combination of strength (minimum 350lbs breaking strength) and flexibility. A thicker cable (3/32” or 1/8”) would have offered far greater strength, but it would be unnecessary in the application and sacrifice flexibility. A smaller cable (3/64”) would have offered a reasonable amount of strength (215lbs minimum break strength), and excellent flexibility, but eyelet sizes are somewhat limited in this smaller size of cable. As you’ll see later, this lanyard has a unique eyelet. The cable itself is 7x7 stranded stainless steel aircraft cable (Figure 1).
Stainless steel was chosen in order to hold up in this marine application. The nylon coating over the cable was chosen for its resistance to wear and tear over time, as well as its resistance to the various chemicals that may be present on deck.
Unique eyelets make for a perfectly suited lanyard
As you can see, this cable has 2 very different sizes of eyelets. The eyelet that is sandwiched underneath the retention nut has a fairly large hole - .500”. This type of eyelet, with a large hole, is generally not available to fit smaller diameter cable – hence the choice to use 1/16” cable, as mentioned above. Most often, when a ½” or larger diameter capture is needed, a loop will be used instead of an eyelet (Figure 2).
Loops versus eyelets – rationale for the choice
Although loops are more labor-intensive, they can cost less than eyelets with large holes due to the custom nature of the eyelet. In this application, however, the customer preferred the eyelet for its bearing surface against the retention nut, as well as its flush fit when sandwiched by the retention nut. Initially, the stem of the eyelet (the portion of the eyelet which is crimped onto the cable) would sometimes interfere with the retention nut. In order to mitigate any possible interference, Pivot Point performs an extra crimp to flatten the portion of the shank near the eyelet, providing a minimum clearance of 1” to the O.D. of the eyelet.
The eyelet on the other end of the lanyard is used to mount the assembly near the scupper using a 14 gage (1/4”) screw. Being used as a mounting point for a screw is a very common use for a lanyard eyelet. As an alternative to the eyelet, some customers opt to use a tab affixed to a loop (See Figure 3) for a similar mounting point, but with more freedom-of-motion. This can help to eliminate stress/bend points that could fray the cable over time, if that is a concern in the application. As mentioned earlier, forming a loop is more labor-intensive than installing an eyelet and, given that this is a more standardized size of eyelet, the eyelet becomes the more cost-effective choice. Since the increased freedom-of-motion didn’t offer much value in this application, the customer settled on the more cost-effective eyelet design.
Ensuring consistent and highest break strength
As is standard for Pivot Point, upon close inspection you’ll notice that the portions of the cable onto which the eyelets are crimped are actually stripped of their nylon coating. This allows for metal-to-metal contact between the end terminals and the cable - promoting the most consistent, and highest, break strength possible.
The Final Result –
While lanyards and tethers are sometimes considered an “afterthought”, care and consideration should be taken when choosing the type, size, and materials. This will help you to design an effectively functioning lanyard at the lowest possible cost.
Let us design your next tethering and fastening solution
Next time you spot a wire rope lanyard out in the world, we hope you’ll stop to take a second look:
- What size and material of cable is being used?
- Is the cable coated or bare?
- What types of end terminals were chosen, and why?
And next time you’re considering tethering something in your application, we hope you’ll reach out to Pivot Point directly – we’d be happy to help!
Do you have a challenging application? Contact us – We love a challenge!
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