How to Understand Reliability and Redundancy Through Surf Fishing
You cannot judge reliability or redundancy until the function statement says what it actually means. It is surf fishing season again, and the slow stretches on the beach keep pulling me back to my reliability and maintenance consulting work. The first two pieces in this series drew some of those parallels. This one uses the four heavy rods on my fishing cart to show how reliability and redundancy both rest on the function statement, including the aspects of it that usually go unsaid.
Start with the Function Statement
Rods and reels have a lot in common with pumps and motors or actuators and valves. All can be bought as a combination or put together by the user. All depend on parts and consumables and work across a range of environmental conditions.
Reliability is measured against a function, so the function comes first. Here is the function statement for my heavy surf class:
The heavy surf rod casts bait past the breakers and lands one- to ten-pound fish in the South Carolina surf in winds up to 15 to 20 mph.
Notice that the rod does not promise fish. Catching fish depends on the angler, the bait, the location, and the tide. The rod's job is to put bait where the fish are and bring them in once they are hooked. A pump is the same way. Its function is a flow at a head, not safe drinking water.
I also expect each heavy rod to do this for 5 to 7 years. That is design life, and I keep it separate from the function.
What the Function Statement Does Not Say
Rough surf calls for heavy weight to hold bottom. In those conditions, I throw 5-ounce pyramid sinkers or 3-ounce sputnik sinkers, and the heavy class has to cast them. That requirement appears nowhere in the function statement above.
It is also debatable. Ask ten surf fishermen whether 4 ounces is enough, or whether pyramids beat Sputniks, and you will get a long conversation. The debate is the lesson. Hidden elements are where people disagree, and they usually do not realize the function statement is what they are arguing about.
Pumps and valves carry the same hidden elements. A valve function statement says open and close but assumes closure time, the differential pressure it must close against, its fail position, and the leakage allowed when shut.
A pump function statement names flow and head but usually does not address duty cycle and what is in the water. That is assumed or unspoken, which means two operators can agree a pump "works" while disagreeing about whether it meets its function.
Adding the hidden element gives a more honest function statement:
The heavy surf rod casts a 5-ounce pyramid or 3-ounce Sputnik sinker past the breakers, holds bottom, and lands one- to ten-pound fish in the South Carolina surf in winds up to 15 to 20 mph.
The Heavy Class on My Cart
These four rods ride on my fishing cart whenever conditions match the function statement.
Big Boy is a Penn Fierce IV 8000 spinning reel on a 10-foot heavy rod. He is the workhorse.
Whitey is a Cabela 5000 spinning reel on a 10-foot heavy rod. The guides break, and the reel parts are slow to get.
No Name is a Penn Fierce IV 6000 spinning reel on a 9-foot medium-heavy rod. It quietly does the job.
Karl Malone is a Penn Fierce 5000 spinning reel on an 8-foot medium-stiff rod. He plays at the top of his weight class.
Other rods, like Tall and Mean Green, cover lighter conditions. The medium class (2500 to 4000 spinning reels on six- to nine-foot rods) handles the full range of spot, croaker, pompano, and whiting in winds of 5 to 15 mph. The light class (1000 to 2500 reels on rods of seven feet or less) is mainly for small fish when the wind is 5 mph or less. Some of these ride on the cart too, depending on the weather, how long I plan to fish, and what I am targeting through the day.
Questions and Answers
A few definitions keep the answers straight. Reliability is the ability to perform the function without failure over a period of time. Dependability, in the old-school sense I use, is mission reliability (once the rod is in action, does it complete the mission?) Availability is whether the rod is ready when I need it, and it is driven by reliability and maintainability together.
Which of your heavy rods are reliable?
Big Boy and No Name are reliable, available, and dependable. They meet the full function statement, including the hidden element, and rarely give me trouble.
Karl Malone meets the function statement, but only just. He will throw a 5-ounce pyramid, and he strains doing it. He is the Mailman, and he delivers. However, I do not want him as my only heavy rod on a 20-mph day.
Every power and water utility has a Karl Malone: the pump that meets its design point only when everything else goes right. It passes the function statement with no margin left, which is worth knowing before the hard day comes.
Whitey is dependable once it is in action. The problem is getting it into action. The guides break and need replacement, and the reel needs regular repair. That is a reliability problem, because it fails too often. The reel parts also take an extended time to obtain, which is a maintainability and supply problem. Together they show up as an availability problem. Availability problems do not come out of nowhere; they are the result of reliability and maintainability.
How do you evaluate redundancy?
I usually fish two heavy rods at a time, so four rods covering two positions gives me N+2. All four operate independently. The rods waiting on the cart are often already baited, which makes them hot standby. Switching takes seconds.
The weakness is common cause. All four rods sit on the same cart in the same conditions. A 25-mph wind takes them outside the function statement together, and no amount of redundancy helps once you are outside it. Three of the four also carry Penn Fierce reels, so a bad parts batch or a design weakness could hit all three at once.
Utilities see the same thing with identical pumps sharing a wet well, a power feed, or a manufacturer. The next piece moves from the cart to the rod itself and looks at common cause inside a single rig.
Are the medium rods backups?
They can be pressed into service, and a stout medium rod might even satisfy the first version of the function statement. The hidden element decides it. A medium rod cannot throw a 5-ounce pyramid into a stiff wind, so it is not redundant.
That does not make it useless. The medium class is degraded-mode capacity, much like a jockey pump that covers average day but not peak. Utilities depend on degraded modes all the time. They just need to be counted as what they are, not as redundancy.
Do you have other heavy rods?
Yes. They no longer meet the function statement, so they are not redundant either. They are my critical spares. When Whitey breaks a guide or a reel needs a part, I go to those rods first. The distinction between installed standby and spares confuses many asset managers and operators. A pump sitting in the warehouse for parts is not the same as a pump piped in and ready to run.
Understanding Reliability and Redundancy
The rods on my fishing cart appear to be interchangeable. At least until you write down the function statement, including the aspects that usually go unsaid. Then one rod becomes marginal, one has an availability problem, and a whole class of backups turns out to be degraded-mode capacity. Your pumps, motors, actuators, and valves work the same way. You cannot judge reliability or redundancy until the function statement says what it actually means.
JD Solomon is the founder of JD Solomon, Inc., the creator of the FINESSE Fishbone Diagram®, and the co-creator of the SOAP criticality method©. He is the author of Communicating Reliability, Risk & Resiliency to Decision Makers: How to Get Your Boss’s Boss to Understand and Facilitating with FINESSE: A Guide to Successful Business Solutions.
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