MIL-DTL-18001L Cathodic Zinc Anode Type ZHC

Lead-freeMIL-DTL-18001L Recessed Bolt Holes No Hardware Protrusion No-Weld Bolt-On Replacement ZHC-23 (23 lb) and ZHC-42 (42 lb)

MIL-DTL-18001L Type ZHC zinc hull anodes with core strap and 2 recessed holes for bolt mounting. Two sizes: ZHC-23 (23 lb) and ZHC-42 (42 lb). Used for ship hull cathodic protection.

Solidus

787°F (419°C)

Liquidus

787°F (419°C)

Density

0.258 lbs/in³ (7.13 g/cm³)

Primary Elements

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Product Overview

MIL-DTL-18001L Type ZHC Zinc Cathodic Anodes are flush-mount hull anodes with a steel core strap and two recessed through-holes for bolt-on installation to ship hulls and offshore structures. The recessed hole design countersinks the bolt heads below the anode face eliminating hardware protrusion that would create turbulence and drag – this makes ZHC the preferred type for hull areas where smooth water flow over the anode surface is important. Two standard sizes are produced: ZHC-23 at 1-1/4″ x 6″ x 12″ (23 lbs) and ZHC-42 at 2-1/2″ x 6″ x 12″ (42 lbs) providing flexibility for different current demand requirements. The recessed bolt design also allows anode replacement by unbolting the depleted anode and installing a new one on the same hull studs without welding – particularly useful for vessels with restricted welding permits or in-water replacement programs. Zinc alloy conforms to MIL-DTL-18001L composition.

Available Forms

1-1/4" x 6" x 12" with Core Strap and 2 Recessed Holes (ZHC-23), 2 1/2" x 6" x 12" with Core Strap and 2 Recessed Holes (ZHC-42)

Product Code

8001ZHC

Technical Info

Thermal Properties

Melting Point (Solidus)787°F (419°C)

Melting Point (Liquidus)787°F (419°C)

Physical Properties

Density (imperial)0.258 lbs/in³

Density (metric)7.13 g/cm³

Primary ElementsZn

SpecificationMIL-DTL-18001L

Lead FreeYes

Key Features

Recessed Bolt Holes No Hardware ProtrusionNo-Weld Bolt-On ReplacementZHC-23 (23 lb) and ZHC-42 (42 lb)

Frequently Asked Questions

Common technical inquiries regarding MIL-DTL-18001L Cathodic Zinc Anode Type ZHC

Surface bolt heads protruding above the anode face create localized turbulence that contributes to hull drag particularly at the leading edge of the anode where flow attachment occurs. Recessed bolt heads sit flush with or below the anode face maintaining a smooth transition from hull plating to anode surface to hull plating. On high-speed vessels and naval ships where hydrodynamic efficiency is critical the cumulative drag reduction from flush-mounted hardware across all hull anodes provides measurable fuel savings. Recessed bolts also protect the fasteners from mechanical damage during drydocking operations.

The ZHC bolt-on design allows divers to replace depleted anodes between drydockings using standard underwater tools. The diver uses a wrench or socket on the recessed bolt heads to remove the old anode from the hull studs then positions the new anode over the studs and tightens the bolts. No welding equipment is required and the hull studs remain in place permanently. This capability is valuable for vessels operating in highly corrosive environments where anodes deplete faster than the drydocking schedule and for navy vessels and offshore platforms where unplanned corrosion protection loss cannot be tolerated.

ZHC-42 is specified for high-current-demand areas of the hull - stern sections near propellers, rudders, and shaft brackets where galvanic current demand from bronze and stainless components is highest; poorly coated or bare steel areas; and installations where a 5-year drydocking interval requires more zinc mass per anode position. ZHC-23 is used for lower current demand areas - forward hull sections, well-maintained paint systems, freshwater or reduced-salinity zones, and supplementary anodes filling gaps in the protection array. The two sizes allow the cathodic protection designer to optimize zinc mass placement rather than using the same anode everywhere.