Martyr CMM25 Zinc Hull Anode | 9.08” x 3.25” x 0.72” | Bolt-On | Saltwater

Martyr Zinc Hull Anode — CMM25 | Saltwater

A mid-size bolt-on zinc hull anode for saltwater use. The CMM25 mounts flush to the hull using its pre-drilled bolt hole pattern and provides sacrificial galvanic protection for the surrounding hull structure, through-hulls, and underwater metal fittings. Larger than the CMM24, it offers more sacrificial mass for vessels requiring greater hull protection coverage or longer service intervals between replacements.

Zinc is the traditional choice for saltwater environments. If you operate in freshwater, a magnesium alloy hull anode is the correct choice for that water type.

Part Information

• Part Number: CMM25
• Brand: Martyr Anodes
• Anode Material: Zinc
• Anode Type: Bolt-On Hull Anode
• Best Use: Saltwater environments

Dimensions

• Length: 9.08” (230.6 mm)
• Width: 3.25” (82.6 mm)
• Height: 0.72” (18.3 mm)
• Note: Hole dimension refers to the distance between mounting holes — confirm bolt pattern against your hull fitting before ordering

Compatible Applications

• Steel, aluminum, and fiberglass hull installations — bolt-on hull anode position
• Vessels requiring greater sacrificial mass than the CMM24 provides
• Saltwater operating environments

CMM Series — Choosing the Right Size

• CMM24 — smaller bolt-on zinc hull anode (4.36” x 1.92” x 0.7”)
• CMM25 (this part) — larger bolt-on zinc hull anode (9.08” x 3.25” x 0.72”)

Related Hull Anodes

• Martyr CMDIVERZ Zinc Hull Plate Anode – ½” x 6” x 12” — larger zinc hull plate anode
• Martyr CMDIVERHZ Heavy Zinc Hull Plate Anode – 1” x 6” x 12” — heavy-duty zinc hull plate
• Martyr CMDIVERMINI Zinc Mini Hull Plate Anode – 6” x 4” x ½” — compact zinc hull plate anode
• Martyr CMDIVERA Aluminum Hull Plate Anode – ½” x 6” x 12” — aluminum option for saltwater and brackish water
• Martyr CMDIVERM Magnesium Hull Plate Anode – ½” x 6” x 12” — magnesium option for freshwater

Service Interval

Inspect hull anodes at every haulout and replace when worn to approximately 50% of original size. In high-galvanic marina environments or areas with significant stray current, inspect more frequently as depletion rates can vary considerably.

Parts Desk Insights

The CMM25 is the better choice over the CMM24 when you need more sacrificial mass in a bolt-on hull anode — either because the CMM24 depletes too quickly between haulouts, or because the hull area being protected is larger. As with all hull anodes, the most critical installation detail is ensuring the anode base makes direct metal contact with the hull: any paint, coating, or sealant between the anode and the hull surface will electrically isolate it and render it ineffective. For the broadest hull protection on larger vessels, the full-size CMDIVERZ zinc plate anode provides the most sacrificial mass in the Martyr hull anode range. If your boat operates in freshwater, switch to a magnesium alloy anode — zinc won’t corrode fast enough in low-conductivity water to provide meaningful protection.