Applying the guidelines on commercial vessels
The 'National biofouling management guidelines for commercial vessels' 
PDF [880kb] recommend maintenance practices for each of the following biofouling prone areas:
antifouling systems
sea chests
sea inlet pipes and overboard discharges
niche areas – painted
niche areas – unpainted
internal seawater systems
These are summarised below.
Antifouling systems
Use an antifouling coating that is appropriate for your vessel’s operating profile including:
- the planned docking cycle
- vessel speed and activity
- projected lay-up periods.
Make sure that you completely remove all biofouling residues and other contaminants when preparing hull surfaces for antifouling repairs or recoating. This will ensure good adhesion and durability of the new coating.
Sea chests
Mussels can be clearly seen on this sea chest grate. Prolific pests like black-striped mussel can clog sea water intake systems causing mechanical damage.
Image courtesy of Cawthron Institute
Avoid this level of biofouling by incorporating the following practices into your maintenance procedures:
- Use an antifouling coating suited to the flow conditions in the sea chest. Carefully apply both anticorrosive and antifouling coating to ensure adequate film build and adhesion to corners and edges.
- Ensure that marine growth prevention systems are operating at a level that is effective in preventing build-up of biofouling.
- Regular use of steam blow-out pipes, where fitted, may minimise biofouling growth in the sea chest.
- External surfaces of the blow-out pipes and holding brackets must be effectively antifouled as they are prone to biofouling.
- Coating durability and adhesion are improved if sea chest angles are bevelled or rounded and the bars on sea chest grates are round rather than angular.
- Hinged grates will allow diver access for in-water inspection and maintenance between dockings. Note that there are restrictions on in-water cleaning in Australia.
Sea inlet pipes and overboard discharges
Apply antifouling coatings to the inside of pipe openings and accessible internals.
Niche areas – painted
Niche areas such as this fin stabiliser are particularly susceptible to biofouling, even though they have had an antifouling coating applied. They require thorough cleaning and their antifouling coating renewed during maintenance.
1) Docking support strips (DSS)
- Vary the position of docking blocks and supports at each docking to ensure that the areas under the blocks are recoated at least every alternate docking.
- At each docking that the strips are accessible, prepare the surface as if they are to undergo a major antifouling refurbishment.
2) Bow and stern thrusters
- Routinely apply high performance coating systems to thrusters and the area around them as they are prone to damage through cavitation forces.
- Coating durability and adhesion are improved if tunnel openings are rounded and grates are constructed of round bars.
3) Bilge keels, cooling scoops and propulsion scoops
- Stripe-coat the outer edge of bilge keels and scoops and weld joints with additional anticorrosive and antifouling coating to ensure adequate film build to optimise system durability and antifouling life.
4) Rudder hinges and stabiliser fin apertures
- Carefully and effectively clean and reapply antifouling coatings to all recesses within rudder hinges and behind stabilizer fins at maintenance dockings.
- Move rudders to port and starboard during the painting process to ensure that all surfaces are correctly covered according to the manufacturer’s specifications.
- Inspect these niche areas between dockings and remove biofouling ensuring that debris is captured and disposed of at licenced onshore facilities. Note that there are restrictions on in-water cleaning in Australia.
Niche areas – unpainted
Some niche areas (such as anodes, velocity probes and echo sounders) are not coated with an antifoulant for operational reasons.
1) Cathodic protection anodes
- Minimise the opportunity for biofouling to accumulate in niche areas by flush-fitting anodes to the hull, or inserting a rubber backing pad between the anode and the hull.
- If the anode is not flush-fitted, the hull surface under the anode and the anode strap should be stripe-coated with an antifoulant to prevent biofouling
- If anodes are attached by bolts recessed into the surface, caulk the recess to remove a potential niche.
- Regularly inspect in-water and maintain cathodic protection anodes to keep them free of biofouling.
- Remove any growth on the cathodic protection anodes, ensuring that biofouling debris is captured and disposed of to licenced on-shore facilities. Note that there are restrictions on in-water cleaning in Australia.
2) Echo sounders and velocity probes
- Regularly inspect surfaces of echo sounders and velocity probes that are not coated with an antifoulant.
- Remove any biofouling, ensuring that debris is captured and disposed of at a licenced on-shore facility. Note that there are restrictions on in-water cleaning in Australia.
- Internally coat any retractable pitot tubes with an antifoulant.
3) Propeller and shaft
Note the antifouling starting to accumulate on the more protected areas of the propeller near the shaft. Regularly polish propellers to maintain operational efficiency and to prevent biofouling.
- Consider coating propellers and propeller shafts with a fouling release coating to maintain efficiency and enable self-cleaning.
- Clean unpainted propeller shafts at the same time as the propeller.
- Routinely inspect thruster propellers or propulsion units and remove any biofouling, ensuring that debris is captured and disposed of at a licenced on-shore facility. Note that there are restrictions on in-water cleaning in Australia.
- Carefully coat exposed sections of stern seal assemblies and the internal surfaces of rope guards with an antifouling coating appropriate to the degree of water movement over and around these surfaces.
Internal seawater systems
- Regularly operate and monitor marine growth prevention systems fitted to internal seawater systems to ensure effective biofouling control is maintained.
- Closely monitor any seawater system operating whilst in port as it will be particularly vulnerable to biofouling.
- Treat to remove any accumulated biofouling.
