ANCHORS and ANCHOR CHAINS

Coating Systems for Anchors
Ship Anchor
Seaman James Todd paints the starboard anchor of
USS KEARSARGE (LHD 3) while anchored in Onslow Bay.
U.S. Navy photo by Photographer’s Mate 3rd Class
Angel Roman-OterMarch 2016.
Overview

Anchors are used to moor surface ships to the bed of a body of water. Anchors are exposed to the harsh corrosive environment of seawater through sea spray as well as full immersion.

Typical Coatings Used
Primer and Intermediate Coat

The primer and intermediate coats are anticorrosive epoxy coatings that are qualified to MIL-PRF-23236, Coating Systems for Ship Structures. The MIL-PRF-23236 specification divides the coating system into four types based on the volatile organic compound (VOC) content. This specification has nine classes of coatings that are determined by the type of surface being preserved. For surface ship bow anchors, acceptable coatings include MIL-PRF-23236 Types V, VI, or VII; Class 5 or 7. Anchors below the lower boottop are coated in accordance with the underwater hull anti-corrosion/anti-fouling system.

Topcoat

The topcoat consists of a high-gloss, low solar absorption (LSA), haze gray polysiloxane or silicone alkyd qualified to MIL-PRF-24635, Coating Systems, Weather-Resistant, Exterior Use. For surface ship bow anchors, acceptable coatings include MIL-PRF-24635 Types III, V, or VI; Class 1; Grades B or C. Anchors below the lower boottop are coated in accordance with the underwater hull anti-corrosion/anti-fouling system.

Low Solar Absorption (LSA) Coatings

Low solar absorption (LSA) coatings are designed to reduce the heat load and infrared signature of the ship. Interior compartments with one or more bulkheads forming a section of the superstructure stay cooler during warm weather, which benefits both sailors and equipment. LSA topcoats contain additional pigments that increase reflectance without sacrificing color or gloss.

Surface Preparation

To ensure coating adhesion, special attention should be paid to the surface preparation in accordance with NSI 009-32. Coating application requires preparation by abrasive blasting in accordance with SSPC-SP 10/NACE No. 2, Near-White Blast Cleaning or SSPC-SP 6/NACE No. 3.For MCM class ships, use walnut shells, garnet, or crushed glass for abrasive blast media. Waterjetting in accordance with SSPC-SP WJ-2/NACE WJ-2, Very Thorough Waterjetting, may be used in place of SSPC-SP 10/NACE No. 2, Near-White Blast Cleaning. Waterjetting in accordance with SSPC-SP WJ-3/L, Thorough Waterjetting, may be used in place of SSPC-SP 6/NACE No. 3.

The surface metal must be degreased following abrasive blast with walnut shell media. Any traces of residual oil will degrade paint adhesion. Appropriate safety precautions for working with flammable solvents must be enforced. Alternatively, a vigorous soap and water wash followed by pressurized fresh water rinse may be used. Do not use a detergent and fresh water washdown when using aluminum oxide abrasive blast media.

Depot Repairs

NSI 009-32 is the governing document for preservation requirements. Permitted coatings are specified in Table 5. All anchor coating system preservation efforts must be accomplished in accordance with NSI 009-32.

Ship’s Force Repairs

Ship’s force personnel are responsible for the anchor coating system integrity until repair activity maintenance is scheduled. Naval Ships Technical Manual: Chapter 631 (NSTM 631), Preservation of Ships in Service – General provides requirements, instructions, and guidance for surface preparation and coating application.

New Construction Installation

New construction ships are painted in accordance with the ship build specification for that class of ship.

Coating Systems for Anchor Chains
Overview

Anchor chains are constantly abraded as the anchor is raised and lowered. Anchor chains are routinely exposed to corrosive seawater. Coating systems used to protect anchor chains must therefore be both corrosion and abrasion resistant.

Anchor chains are prepared for coating by commercial blast cleaning to SSPC-SP 6, then coated with an epoxy siloxane coating system.

Typical Coatings Used
Primer Coat

The primer coat consists of an anticorrosive coating qualified to either MIL-PRF-24635, Coating Systems, Weather-Resistant, Exterior Use; or MIL-PRF-23236, Coating Systems for Ship Structures. For anchor chain, acceptable coatings include MIL-PRF-24635, Types V or VI, Class 1; and MIL-PRF-23236, Types VI or VII.

Topcoat

The topcoat consists of a high-gloss silicone alkyd qualified to MIL-PRF-24635, Coating Systems, Weather-Resistant, Exterior Use. For anchor chains, acceptable coatings include MIL-PRF-24635 Types V or VI, Class 1. Note that anchor chain and detachable links are marked and color coded in accordance with NSTM Chapter 581, unless otherwise directed by the applicable Work Item.

Surface Preparation

To ensure coating adhesion, special attention should be paid to the surface preparation in accordance with NSI 009-32. Coating application requires preparation by abrasive blasting in accordance with NACE No. 3/SSPC-SP 6, Commercial Blast Cleaning.

Surface Preparation (MCM Class Ships)

For MCM class ships, use walnut shells, garnet, or crushed glass for abrasive blast media. Waterjetting in accordance with NACE/SSPC-SP WJ-3, Thorough Waterjetting, may be used in place of NACE No. 3/SSPC-SP 6, Commercial Blast Cleaning.

The surface metal must be degreased following abrasive blast with walnut shell media. Any traces of residual oil will degrade paint adhesion. Appropriate safety precautions for working with flammable solvents must be enforced. Alternatively, a vigorous soap and water wash followed by pressurized fresh water rinse may be used. Do not use a detergent and fresh water washdown when using aluminum oxide abrasive blast media.

Depot Repairs

NSI 009-32 is the governing document for preservation requirements. Permitted coatings are specified in Table 5. All anchor chain coating system preservation efforts must be accomplished in accordance with NSI 009-32.

Ship’s Force Repairs

Ship’s force personnel are responsible for anchor chain coating system integrity until repair activity maintenance is scheduled. Naval Ships Technical Manual: Chapter 631 (NSTM 631), Preservation of Ships in Service – General [insert link to page] provides requirements, instructions, and guidance for surface preparation and coating application.

New Construction Installation

New construction ships are painted in accordance with the ship build specification for that class of ship.