Maddox Calculator

Find the Right Maddox Anode for Your Boat

Not sure which Maddox Anode is right for your boat? Simply answer a few quick questions and our calculator will recommend the most suitable option for your vessel. Based on Marine Protection Systems' expert Maddox anode specification guide, it's the quickest way to choose the right anode with confidence and keep your boat protected from corrosion.

We highly recommend that before getting started, you click the red ! icon in the top right of the Maddox Calculator and read the Important Information. It includes important guidance and exceptions for aluminium drives, sterndrives/outdrives, thrusters, stainless steel appendages, and anode maintenance.

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Maddox Calculator

Corrosion Control That Works

Design Calculation Considerations

Water Type: This calculator has been designed for saltwater and brackish water applications. In very low salinity (highly brackish) environments, protection of low-potential metals may require additional Maddox Anode surface area. Where appropriate, select the next larger recommended anode size.

Protective Coatings: All recommendations assume protective coatings are applied to underwater metals to help achieve maximum efficiencies. If protective coatings are not present, increase recommended anode capacity by ~30%.

Design Life: Recommended anode sizing is based on a minimum 12-month design life. Actual service life may vary depending on water flow, vessel usage, salinity, water temperature and other environmental conditions.

Shaft Drive & Bonding System

For salt & brackish water, bonded shaft-drive vessels (thru-hulls, fittings, rudders, trim tabs included in the bonding system).

Important: Maddox recommendations for swim platforms apply only to stainless steel swim platforms connected to the vessel's bonding system. Aluminium swim platforms should be electrically isolated from the main bonding system and protected locally using aluminium or zinc anodes (aluminium preferred).
Recommended Shaft & Bonding System Protection
Recommended anode
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Shaft note: Shaft coverage includes bonded fittings — thru-hulls, fittings, rudder(s) and trim tabs. Areas of high water flow and/or large appendages may need local anodes or increased anode surface area.

Trim Tabs — Stainless Steel Only

If anodes are already present, replace zincs with a similarly sized MDX.

Recommended Maddox Anodes
Trim tab anode
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Swim Platforms — Stainless Steel Only

If anodes are already present, replace zincs with a similarly sized MDX.

Recommended Maddox Anodes
Swim platform anode
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If electrically isolated, swim platforms can be protected via Maddox Anodes even if other parts of the boat require protection via a higher-potential anode. Electrical isolation must be confirmed and maintained.

IPS Drives — Replace Volvo Aluminium with MDX

IPS units should be maintained and electrically isolated from the engine & bonding system. Single anode per IPS.

Recommended Maddox Anodes
IPS anode
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For vessels with a greater bonding system, refer to the single-drive MDX specification guide.

Important Information

General guidance not covered by the calculators below.

Aluminium Drives on GRP Boats

Any alloy drives (sail drive, outboard, Zeus drive, sterndrive, etc) must use zinc or aluminium anodes. Use only the OEM specified anodes and do not replace with Maddox.

Ensure all anode composition is the same for commonly bonded systems.

For best performance on stainless steel swim platforms & trim tabs — isolate appendages and use Maddox on components, or run separate (isolated) bonding to a Maddox anode for ideal protection. A minimum of 200 ohms is required between drives and the Maddox anode to confirm isolation.

Sterndrive / Outdrive

Sterndrives, outdrives and outboards should continue using the manufacturer's specified aluminium anodes (OEM specification) — these bonded OEM drive components should not be replaced with Maddox.

However, electrically isolated stainless steel appendages — such as trim tabs and stainless swim platforms — may be protected using Maddox Anodes where appropriate. This distinction between bonded OEM drive components and isolated stainless accessories is particularly important for the North American market.

Thrusters

Electric thrusters — ensure isolation from the bonding system and use factory anodes. Maddox MDXBT can be used on bronze/stainless steel thrusters.

Hydraulic thrusters — use MDXBT on the thruster body, or ensure electrical isolation and use factory anodes.

Anode Maintenance

Anodes should be checked for continuity regularly with a visual inspection to ensure they remain active.

Disclaimer: Marine Protection Systems has made every effort to ensure the information provided in this calculator is accurate at the time of publication. Marine Protection Systems expressly recommends that the user make their own assessment to determine the suitability of the product for its intended purpose prior to application. MPS shall not be responsible for loss, damage, or injury resulting from reliance upon, or failure to adhere to, any recommendations or information contained herein; nor from abnormal use of the material; nor from any hazard inherent in the nature of the material. This material remains the exclusive property of Marine Protection Systems Pty Ltd and must not be reproduced, replicated, copied or used without the expressed consent of Marine Protection Systems Pty Ltd. Source: GRP Maddox Anode Specification Guide, © FEB 2022.