Not surprisingly, the term seafastening is widely used throughout the breakbulk industry. In fact, you could go as far as to say that seafastening is the backbone of breakbulk. Here at breakbulk.news, wanting to learn more, we contacted Houston-based naval architect and heavy lift engineer Ryan Boyd to give us a broad overview of this important subject.
Before speaking to Ryan Boyd, we knew the point of seafastening was simple: to keep the cargo secure as the ship sails from A to B. What we learned, however, is that this general description is deceptive of what is actually an extremely complex subject.
“For effective seafastening, the first step is to look at the movement of the vessel,” begins Ryan. “Ships move in six degrees of movement, surge, pitch, sway, roll, heave and yaw. All that movement creates accelerations. This is shown in the most fundamental equation: F=MA, or Force = Mass x Acceleration.”
The importance of weight & height
While the ship-owner or the ship’s technical team typically provides the data on the acceleration forces experienced on a ship, Ryan says that it is important to note that accelerations – and therefore, seafastening loads – are different for every type of vessel and every operating condition. “Open ocean voyages are totally different from river cargos. The weather is also a determining factor, as is the duration of the trip.”
The F=MA equation has some crucial implications.
“The further away the cargo is from the ship’s centre of gravity, the higher the accelerations will be. This is why tall and skinny cargoes like cranes can be so challenging.”
The weight of a cargo also plays a key role. “For the breakbulk industry, whether you are transporting a statue of an elephant, a nuclear reactor, or a container full of water, the thing that I am most concerned about is weight. The heavier your cargo is, the stronger your acceleration forces will be. Where you position the cargo on the vessel also affects the acceleration forces; this means that you sometimes have to get creative to reduce the accelerations – put the cargo in the hold instead of on the deck, or move it to a mid-ships position.” Adding to the list of determining factors, Ryan notes that it is important to identify how much accelerations the cargo itself can withstand. “For example, some cargoes may have delicate internal systems restricting the accelerations and forces that can be imposed on the item.”
Lashing materials
Knowing that the accelerations exerted on a ship and its cargo tell you how strong your seafastening material has to be, how do heavy lift engineers deal with the unpredictability of the maritime environment? In other words, what happens if you plan for 2-metre high waves, but then encounter 4-metre high waves? “Typically with sea state conditions you are designing to a 1 in 100, 1 in 500, etc wave height. This is based on the statistics of the environment the ship is operating in. Encountering a worse condition than what was expected is unlikely, but is always a possibility. In this event there is a bit of extra capacity in your lashing materials. Most surveyors use a 2.25 safety factor for lashing. They look at the breaking point of the lashing material, and divide that figure by 2.25 to get the Safe Working Load. This safety factor also accounts for any inconsistencies or impurities in the lashing material.”
This brings us to the subject of lashing materials, of which there are three main types: chains, wire rope, and nylon. Here are the key lessons we learned from Ryan about lashing materials.
- Chains
Chains are a solid metal – they last a long time and can be used time and time again. On the other hand, they come in fixed lengths, which gives fewer lashing options. Turn buckles used for tightening chain can be dangerous. They are also heavy – fragile cargo will need protection.
- Wire rope
Wire rope is cheaper than chain and comes in a variety of sizes, making it more versatile than chain. You can cut the length you need from a spool of wire rope. However, wire rope is more or less for one-time use and typically requires multiple personnel to make up the length and clamp down the clips.
- Nylon
Nylon is not as strong and it is expensive, but it is easy to handle and light. While a 10-metre length of chain will sag in the middle, nylon is easier to tighten. What’s more, lashing with nylon is fast.
Ryan describes the decision-making process of what lashing material to use as “a juggling act”. In choosing between nylon and chain, for instance, nylon is not as strong as chain and it is more expensive, but lashing operations can be done by just one person. However chain and wire rope are typically the go-to lashing material for seafastening of breakbulk cargo.
Spread the load
There are a number of shared rules for all lashing materials. First and foremost, they need to be certified. Next on the list is that lashing is not a situation for mix-and-match. “The different lashing materials have different stretching properties. If you mix them, it’s like putting three different-sized wheels on your car. This is not the case for when you use different materials in different directions of force,” Ryan adds. Another point of note is load spreading. “If your cargo is heavier than the load bearing capacity of your deck, then you will need to consider steel mats, wooden mats or beams to spread the load.”
Whatever lashing material is used, it will have to be secured to the deck; this is most commonly accomplished with a welded D-ring. “It is important to have an efficient D-ring plan. This maintains optimum angles of lashing materials in their lateral, transverse and longitudinal positions, and because you can use them numerous times, this saves a huge amount of time and money for welding, inspections and gas-free certification.”
D-rings are most certainly not the only time that the welders are brought in for seafastening tasks. “If a temporary support like a saddle or cradle is used, then this can be welded to the deck,” explains Ryan. “Another option are stoppers, which can be welded to the deck next to the cargo; these prevent transverse and longitudinal movement. And if the cargo’s centre of gravity is higher and tipping is possible, then a clip can be used to prevent uplift.”
Future development
Does Ryan see room for innovation in the subject of seafastening? “I don’t see any innovations in terms of materials,” he replies. “The materials currently used are what they are – they all have a grade and a strength. However, as an engineer working for my customers or employers, I innovate by figuring out more efficient layouts or loading plans that save time, money and equipment. While still being safe and secure.”
“However, innovations to reduce ship motion are feasible. And because transport logistics is a crucial part of the process, I do think that innovations will come from the design side. It would help tremendously if the companies designing items needing to be secured for seafastening engaged heavy lift companies about how to transport the cargo from point A to point B during the design phase. We do see this on some occasions, but typically seafastening and lashing is an afterthought. The wind industry is making every effort to optimize and increase efficiencies, so you do see consideration put in to the transport of equipment. For example, cradles/cages for wind blades and lifting/lashing padeyes on nacelles.”
This last point makes us realise that maritime seafastening is indeed just the tip of the iceberg of factors to consider in the transport logistics of breakbulk cargo.
“You can’t talk about seafastening without talking about planning the logistics of the whole journey of a cargo, which might include transport by barge and truck as well as by ship. And then there’s the loading process to discuss – whether it’s with a crane, the ship’s own crane or with an SPMT. That is a whole operation in itself.”
If you know more about seafastening and want to share your insights with us, you can reach the team at editor@breakbulk.news
