Martyr CMT21 Zinc Teardrop Hull Anode – 5" x 2" x 0.8" | Bolt-On | Saltwater
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Martyr CMT21 Zinc Teardrop Hull Anode
A mid-size zinc teardrop hull anode designed for bolt-on installation on hulls, keels, rudders, and other underwater surfaces in saltwater. The teardrop profile delivers a low-drag, hydrodynamic shape that sheds water cleanly and minimizes resistance while providing reliable sacrificial protection against galvanic corrosion. At 5" long, the CMT21 offers more sacrificial mass than the compact CMT20, making it a better fit for larger vessels or longer intervals between haulouts.
Compatible Applications
- Steel, aluminum, and fiberglass hulls in saltwater
- Rudder faces, keel leading edges, and flat underwater surfaces
- Mid-size to larger inboard and outboard vessels
- Any application requiring a mid-format teardrop bolt-on zinc anode
- Upgrade from the CMT20 when more sacrificial mass is needed
Specifications
- Part Number: CMT21
- SKU: 194-CMT21
- Material: Military-grade zinc alloy (sacrificial)
- Dimensions: 5"L × 2"W × 0.8"H (approx. 127mm × 51mm × 20mm)
- Profile: Teardrop / hydrodynamic
- Mounting: Bolt-on
- Best For: Saltwater
- Weight: ~220 g
Alloy Selection Guide
Teardrop hull anodes are available in three alloys for different water types:
- Zinc – saltwater (open ocean, consistent high salinity) – CMT21 (this product)
- Aluminum – saltwater & brackish water (coastal, estuaries, mixed salinity)
- Magnesium – freshwater only (lakes, rivers, reservoirs)
Related Hull Anodes
- Martyr CMT20 Zinc Teardrop Hull Anode – 3.4" × 1.8" (smaller)
- Martyr CMT-T20 Zinc Teardrop Hull Anode – 3-1/2" × 1-3/4"
- Martyr CMT-T21 Zinc Teardrop Hull Anode – 5-1/4" × 2"
- Martyr CMMZC406 Zinc Hull Plate Anode – 4.4" × 9"
- Martyr CMDIVERHZ Heavy Hull Plate Anode – Zinc 1" × 6" × 12"
- Martyr CMDIVERZ Zinc Diver’s Dream Hull Anode – ½" × 6" × 12"
Parts Desk Insights
The CMT21 is the right teardrop anode when the smaller CMT20 isn’t providing enough mass for the vessel’s protection requirements or haulout interval. The teardrop shape is preferred over flat plate anodes in areas with water flow — it sheds water cleanly and creates less drag than a flat profile of equivalent mass, making it a good choice for rudder faces and keel leading edges where hydrodynamics matter.
Zinc is the correct alloy for full saltwater use. If your vessel operates in brackish or mixed-salinity water, an aluminum teardrop anode is the better choice — zinc can passivate in lower-salinity conditions and lose effectiveness. For freshwater, magnesium is the only alloy that provides meaningful protection.
Shipping information
In-stock and OEM parts: ship same or next business day.
Locally warehoused items: ship within 3–4 business days.
Special-order items: timeline confirmed after order.
Returns & warranty
Returns & Satisfaction Guarantee
We stand firmly behind the quality of every product we sell. Your confidence matters to us — and we back it with a straightforward 30-Day Satisfaction Guarantee.
If you are not fully satisfied, you may request a return within 30 days of delivery. All returns must receive pre-approval prior to being sent back. Unauthorized returns will not be accepted.
To qualify for a return:
Item must be in new, unused condition
Product must be in its original packaging
All parts, components, hardware, manuals, and accessories must be included
Packaging must be undamaged and suitable for resale
Important:
Electronics are strictly inspected. No returns on open-box electronics. Exceptions may apply only with prior written approval. Any electronic unit that has been installed, powered, activated, or altered may not be eligible for return.
We are serious about product integrity — and equally serious about taking care of our customers. If there is ever a product issue, contact us immediately so we can make it right.
For return authorization, please contact our support team before shipping anything back.