Introduction: Upper net sections stay near the surface because float lines, panel weight, and water uptake work together, and no single material property carries the whole job.
When a purse seine or any net with a floating headrope is set around a school of fish, the top edge of the net has to stay at or very near the surface. If that upper panel sags, fish move over the top and the set is wasted. That is why crews pay attention to how much the netting in the upper section weighs, how much water it takes on during a set, and how well it hangs on the float line. Those three factors decide whether a floating section does its job, so it is worth understanding how they connect in day-to-day commercial fishing gear.
An upper net section is the part of the net that hangs from the float line — the meshes between the top edge and the point where the weighted lower section starts to dominate the panel. In a purse seine, that upper panel works with a floating line at the top, while a weighted line and purse rings sit at the bottom, and the whole gear is set in a circle around a school and then closed underneath. NOAA's description of purse seines treats the floating line, the floats along it, and the weighted lead line as one assembly, which is exactly how crews see it on deck: the float line and the top panel are a single working unit, not two separate parts.
The float line is what actually holds the net at the surface, and its buoyancy is a fixed budget. Each float along the line provides a certain amount of upward force, and everything hanging below it draws against that budget — the upper panel, the rest of the net, the rings, the purse line, and eventually the catch. A light upper panel leaves more of that buoyancy available for keeping the headrope high when the gear is loaded or working against current. That is why the weight of the upper section, and the way it is hung, matters more than the weight of the net as a whole. Polypropylene netting is light in the water, and it comes in forms that support this kind of build: cut panels and finished nets with border finishing and rope attachment can be made to fit a specific float line.
Absorbed water shows up twice in a fishing day: during hauling and during stacking. Crews bring the net in with a power block or winch, and a panel that has taken on water is heavier for the machine and for the people flaking it down. Nylon is the usual comparison point, because it takes on noticeably more water and holds it, while polypropylene is a non-polar fiber that picks up very little. That difference shows up as less wet weight swinging over the side, less strain on the line, and a net that dries faster between sets. It also shapes how the upper panel behaves next time it enters the water, because a panel still heavy from the previous set hangs differently on the float line.
Polypropylene has a density lower than water, so the fiber itself tends to float rather than sink. That is a different starting point from nylon and polyester, which are denser than water and depend on added flotation to stay up. For the upper section of a net, that natural tendency means the panel is not fighting the float line. Combined with a light twine and sensible hanging, the upper section stays where it should while the lower section does the containment work. Gear designers also treat mesh size and mesh shape as selectivity tools, so the upper panel is never only a weight question — it is part of how the gear selects and holds fish, and the material choice has to serve that role. The handling side matters just as much. Polypropylene netting absorbs very little water, so a wet panel does not turn into a much heavier panel over a long soak. Crews working a purse seine or a similar encircling gear move large amounts of net in a short window, and trimming weight from the upper section reduces the load on every haul. The material also comes in several forms, which matters when matching an upper panel to a float line: raw netting, cut panels sized to a given length and depth, and finished nets with edge border finishing and rope attachment. Plfishery produces polypropylene netting across those three forms and supports custom mesh size, depth, and color, which is the kind of flexibility an upper-section build usually needs. ICES working group material on fishing gear treats netting drag and mesh mechanics as a system question — how a panel behaves depends on twine, mesh opening, hanging, and rigging, not on fiber type alone. Polypropylene fits into that picture as a low-density, low-absorption fiber that suits floating sections, and the Marine Stewardship Council's gear background points in the same direction when it describes mesh size and gear modification as tools that shape what a net catches and how it performs.
Low water absorption is one input into buoyancy, not the whole result. Whether an upper section actually stays at the surface depends on the assembled gear: the size and number of floats, the diameter and length of the float line, how the panel is hung, how much rope and hardware hang below it, and how much catch the gear is holding. A very light, low-absorption panel on an undersized float line can still sink, and a heavy panel with generous flotation can still float. Buoyancy is the outcome of a whole working system, and the panel is one part of it. The same logic applies to strength and weathering. Polypropylene resists water uptake well, but how long a net lasts depends on twine size and construction, mesh size, knot or knotless structure, how the panel is assembled, and how the gear is actually fished. Abrasion on deck and alongside the hull, UV exposure between sets, and fouling from marine growth all play a role. Fouling deserves a mention, because algae and attached organisms add weight that no fiber property can offset. Cleaning, inspection, and replacing worn sections remain part of keeping an upper panel performing the way the crew expects.
For upper net sections, the useful way to think about polypropylene is in terms of what hangs on the float line: total weight in the water, how much that weight grows during a set, and how well the panel matches the flotation already built into the gear. Lightweight netting with low water absorption helps on all three counts, but it works best when float line, hanging, and finishing are chosen together as one design. Buyers comparing upper-section options can look at mesh size, twine, panel depth, and how the edges and rope attachments will be finished, then match that against the flotation they already run.
A：Because the upper section hangs from the float line, and every kilogram there draws against the buoyancy available to keep the headrope at the surface. Light netting leaves more of that buoyancy free for holding the top of the net high when the gear is loaded or working in current, and it is also easier to haul, flake down, and stack on deck between sets.
A：The float line and the upper panel behave as one assembly. Floats along the line push the headrope up, while the panel, ropes, rings, and catch pull down. Because polypropylene is less dense than water and takes on very little water, the panel adds less downward load than a heavier, water-absorbing alternative, so the same flotation can keep the headrope sitting higher in the water.
A：No. Low absorption only means the netting does not gain much weight from water. Staying at the surface is decided by the whole assembly — float size and count, float line, hanging, hardware, catch load, current, and fouling. Low absorption helps, but it has to be matched with flotation sized for the gear it is rigged on.
Fishing Gear: Purse Seines | NOAA Fisheries
Fishing methods and gear types | Marine Stewardship Council
