Design of ship systems
Shaping your systems together with Cathwell, you may expect in-depth understanding of subsea operations and their design consequences.
Whether you choose to bring us in early in the concept and vessel design phases, or need to consult our engineers about certain performance calculations, we are prepared to assist.
Recommended practice for new-building design with reference to “SFI Group System”
Cathwell has brought out a set of recommended guidelines for spesification of cathodic protection and antfouling treatment for ships. Below is an extract of the guidelines, numbered with reference to the coding structures of SFI:
278 Cathodic protection – external
288 Cathodic protection – internal (ballast tanks, cargo tanks)
721 Antifouling treatment – sea intake/cooling system
ICCP design (SFI code 278)
Protective current density versus coating breakdown for design of underwater hull protected by ICCP (see below table). Further recommended design practice:
- Design lifetime: More than 10 years.
- LPP up to 140 m: 2-4 ICCP anodes (depending on mechanical exposure) and 2 reference cells.
- LPP more than 140 m: 2-6 ICCP anodes (depending on mechanical exposure) and 2-4 reference cells.
- Propeller shaft and rudder stock: To be properly grounded to hull by shaft slip ring system.
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CathSense® ICCP system for corrosion protection of underwater hull
Sacrificial anode design (SFI code 278)
Protective current density for design of underwater hull by protection by sacrificial anodes (see below table). Further recommended design practice:
- Anode alloy: Type approved aluminium.
- Anode lifetime: In accordance with specified docking interval / operation time.
- Thruster tunnels: Anode fastening by welding (not bolting).
Range of anodes for external application for ships
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Antifouling design (SFI code 721)
Recommended practice for design of electrolytic antifouling for sea water intake/cooling by MGPS/ICAF system.
WATER INTAKE SYSTEM
- Antifouling anodes: Cu anodes only, or Cu in pair with Al/Fe anode.
- Cu dosing: Minimum 2 ppb (2 µg/L) concentration of Cu.
- Dimensioning: Unless the Cu dosing can be automatically adjusted according to actual water flow, calculation of dosing to be based on maximum pump capacity.
- Anode utilisation: ≤90 %.
- Design lifetime: In accordance with specified docking interval / operation time.
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BOX COOLER SYSTEM
- Antifouling anodes: Cu anode rods in pair underneath each box cooler.
- Anode utilisation: ≤80 %.
- Design lifetime: In accordance with specified docking interval.
- Anode size: Anode rod length should generally be equal to the box cooler tube bundle width. Rod diameter to be minimum Ø70 for 3 years and minimum Ø80 for 5 years operation time.
Design input request – what we need to assist you
This section applies mainly for newbuild and retrofit, althoug similar details may be relevant in verifying existing designs.
By providing the below listed information (for the system in question), we would be able to carry out a proper design. If not all details are available, we could start with what you have, and adjust as we go along.
Protection of underwater hull (by ICCP or sacrificial anodes)
To calculate cathodic protection of external underwater ship’s hull, the following input would generally be requested:
- GA drawing.
- Docking interval (assumed time of operation between dry-dockings).
- Area of operation (assumed).
- System preference, if any (protection by ICCP or sacrificial anodes).
The inquiry should include the ships name or hull number for which the system is intended.
Anodes for ballast tanks
To calculate cathodic protection of the external underwater hull, the following input would be requested:
- GA drawing.
- Tank type (side tank, double bottom, fore peak, aft peak or similar).
- Tank area/volume.
- Coating condition (assumed).
- Tank content (regular sea water, fresh water, other).
- Ballast time and level (assumed).
- Design lifetime of anodes (2-3 dry-docking periods are typical).
Your inquiry should include the ships name or hull number for which the system is intended.
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Restrictions for use of aluminium alloyed anodes in certain tanks
Antifouling for seawater intakes (MGPS/ICAF)
Details requested to calculate a proposal for antifouling treatment of sea chests, mud boxes and seawater pipings:
- GA drawing and sea chest arrangement drawings (if available).
- Docking interval (assumed time of operation between dry-dockings).
- Pump capacity (flow rate in m3/h) from each of the sea chests subject to antifouling treatment.
- Material quality in seawater pipes (CuNiFe, carbon steel, etc.).
- Area of operation (assumed).
Your inquiry should include the ships name or hull number for which the system is intended. If all the above details are yet not available, we can just assume and adjust as we go along.
Antifouling for box coolers (MGPS/ICAF)
Details requested to calculate a proposal for antifouling treatment of sea chests with box coolers:
- GA drawing and sea chest arrangement drawings (if available).
- Docking interval (assumed time of operation between dry-dockings).
- Area of operation (assumed).
Your inquiry should include the ships name or hull number for which the system is intended.
Propeller shaft grounding (slip ring system)
To design and propose a propeller shaft grounding system, the following information would basically be requested:
- GA drawing.
- Shaft diameter.
Any requests should include name of the vessel for which the work is intended.
