What offshore farming demands

Aquaculture grating lives in salt spray, sun, tide and biofouling. Cage platforms, feeding walkways, grading tables and landing ramps all carry people and all meet seawater, and once the coating on ordinary steel grating is damaged, rust spreads quickly from the break.

Loads on a farm are irregular. Feed sacks, harvest crates and people gather on a walkway at the same time, and the float moves with the waves, so grating and connections see dynamic rather than static load. Describe these conditions in the specification instead of quoting a single uniform load.

Maintenance offshore is expensive. A trip out needs people, tools and spares, and every maintenance visit avoided saves cost. Corrosion resistance, low weight and easy disassembly are the main reasons FRP grating is popular on farms. For common practice on marine projects, see marine and industrial application scenarios

Seawater immersion and resin choice

Chloride ions and water in seawater permeate along the interface between resin and fibre; after long immersion, blistering, whitening and loss of interlaminar strength can appear. Isophthalic or vinyl ester resin with a surface veil slows permeation.

Glass fibre itself resists seawater, but exposed fibre wicks water by capillary action. Cut ends, drilled holes and worn spots must be sealed, which is the detail most often missed in marine use. The sealing resin must be compatible with the panel, and factory sealing is preferable.

Temperature matters less than concentration for seawater attack, but surface water in tropical farms stays warm and ageing runs faster. Where a long design life is required, put water temperature, sunlight and cleaning frequency into the technical conditions together.

Ultraviolet and ageing

Ultraviolet light is the main ageing factor offshore. Under alternating UV and water, the resin surface chalks and changes colour, and glass fibre gradually becomes exposed. A surface veil and UV-resistant coating slow this down but cannot stop it.

Colour choice relates to UV stability. Dark surfaces run hotter with sharper thermal cycling; pale surfaces reflect more sunlight but show dirt more. Farms often use grey or green as a balance between looking clean and staying presentable.

Judge ageing by the surface, not colour alone. When the surface chalks and the fibre pattern is clearly visible, the resin layer has thinned and the panel should be inspected or repaired locally. Regular rinsing with fresh water reduces the salt and dirt left on the surface.

Biofouling and cleaning

Barnacles, algae and shellfish attach to the surface and inside the openings. Fouling adds weight, blocks drainage and makes the walking surface slippery. Farms usually remove it with a high-pressure washer, scrapers or brushes.

The cleaning method affects panel life. A pressure jet held too close damages the resin surface, and heavy scraping scratches the anti-slip grit. Keep a sensible angle and distance, soften the fouling first, and do not attack it with metal tools.

Fouling depends on light and nutrients. Feed areas, cage edges and slow-flow corners foul faster and should be cleaned more often. Designing the grating in liftable sections makes it easier to take out for cleaning.

Some farms use antifouling coatings, but adhesion to FRP and compatibility with the resin must be confirmed. Ordinary antifouling paint is not necessarily suitable for FRP grating, so test a small area first.

Connecting floats and walkways

Walkway grating on a float moves with the waves, so connections matter more than on land. Panels are usually fixed to the float with stainless bolts, clips or clamping strips, and the fixing points must transfer both horizontal and vertical force.

Relative movement between floats subjects the grating to repeated bending. Laying in sections with expansion gaps is more reliable than one continuous run. Gap width should follow float size, wave height and temperature range.

Walkway edges should have handrails or upstands, and panel ends must be fixed against lifting and tripping. On a tilting float the body's centre of gravity shifts, so slip resistance and handrails matter more than on flat ground.

Structural connections should be easy to inspect. Offshore, frequent dismantling is impossible, so bolts and clips should be visible from above and loose items spotted early. Concealed connections look neat but are hard to maintain.

Wet slip resistance

Wet slip resistance is the core requirement on a farm walkway. Seawater, fish mucus and feed residue form a slippery film, and a smooth grating is risky on ramps and landing areas.

A gritted or deeply patterned surface is more reliable wet, but grit wear matters. If the grit is not hard enough for marine use it can polish flat within months. Ask about the grit material and wear class at selection.

Bare feet and rubber boots feel a surface differently. Farm staff mostly wear waterproof boots with deep tread, so a coarser surface is acceptable; where work is done barefoot, avoid sharp projections. To choose a surface for wet duty and footwear, see wet slip-resistant surface selection

Fasteners and galvanic corrosion

Use 316 stainless for fasteners in seawater, and consider duplex stainless for critical connections. Carbon steel bolts rust quickly at sea even when galvanized, and rust water stains the grating surface.

Galvanic corrosion does not occur between stainless and FRP because FRP does not conduct, but it does where stainless meets an aluminium float or a steel frame. Fit insulating pads between dissimilar metals to avoid a galvanic couple. Use bolts and washers of the same grade together, because mixing grades can also start local attack.

Sealing bolt holes matters as well. Seawater that enters a hole stays there and accelerates local ageing. Use sealant or sealing washers during installation and check bolt tension periodically.

Selection, maintenance and whole-life cost

The usual order on a farm is load and span first, then resin and surface, then colour and connections. Load includes people, feed, harvest and wave-induced dynamic load, and estimating on an allowance per person is not enough.

• Settle load, span and dynamic factors together.
• Choose resin, surface veil and edge seal for seawater.
• Keep all fasteners 316; do not mix in carbon steel.
• Hold spares and special tools by area.

Whole-life cost matters more than unit price. FRP grating may cost more up front than galvanized steel, but a replacement offshore carries high labour and vessel cost, and the difference in life changes the conclusion. Compare over service years and maintenance visits.

Keep spares ready. Resupply to an offshore site takes time, so hold a proportion of panels and fasteners from the same batch for local replacement. For the overall case for FRP, see the benefits of FRP grating