11th Sep 2025
Sacrificial anodes are one of the most important, and most overlooked parts of your boat’s protection system. Get them right, and they quietly prevent galvanic corrosion from eating away at your hull, shaft, propeller, rudder and other metal fittings. Get them wrong, and you could face expensive repairs and reduced boat life.
At Anode Outlet, we often see the same fitting mistakes made by boat owners. In this guide, we’ll cover the most common pitfalls - and show you how to avoid them.
1. Choosing the wrong anode metal.
The mistake:
Fitting zinc when your boat lives in fresh water, or magnesium when it’s in salt water. Each environment requires a different anode material. If you use the wrong one, it may dissolve too quickly - or not work at all.
How to avoid it:
- Salt water: Zinc or aluminium anodes.
- Brackish water (estuaries, tidal rivers): Aluminium is usually best.
- Fresh water (canals, lakes, inland rivers): Magnesium anodes.
Always check your boating environment and select the right metal. Aluminium is becoming the most versatile choice, as it works well in both salt and brackish water.
2. Poor electrical contact.
The mistake:
Anodes are bolted to the hull, shaft or rudder - but if the mating surfaces aren’t clean and bright metal, the electrical connection is weak. In that case, the anode can’t protect the metal properly.
How to avoid it:
- Remove paint, oxidation and marine growth before fitting.
- Use a wire brush or abrasive pad on both the anode and the contact area.
- Tighten fixings firmly to ensure metal-to-metal contact.
3. Painting over anodes.
The mistake:
Sometimes, in an enthusiastic antifouling session, owners accidentally coat their anodes with antifoul paint. Once sealed, the anode can’t dissolve - and it becomes useless.
How to avoid it:
- Mask around the anode before applying antifouling.
- After haul-out, always check your anodes are free from paint or coatings.
- If an anode has been painted, replace it immediately.
4. Fitting too few (or too small) anodes.
The mistake:
One small anode is fitted on a large surface area, which provides inadequate protection.
How to avoid it:
- Match the anode surface area to the amount of metal being protected.
- As a rule of thumb: the more underwater fittings, the more anode coverage you need.
- If in doubt, consult an anode sizing chart or speak to a specialist.
5. Mixing anode metals incorrectly.
The mistake:
Some owners fit a mix of zinc, aluminium and magnesium anodes on the same boat. This creates uneven protection and can cause accelerated corrosion.
How to avoid it:
- Stick to one anode metal type throughout the boat.
- If you change from zinc to aluminium, replace all anodes at the same time.
6. Loose or missing anode fixings.
The mistake:
Anodes can loosen during a season, or fixings corrode and break. A loose anode provides poor contact and may fall off completely.
How to avoid it:
- Always use the correct bolts, nuts and backing pads for the anode type.
- Check torque and security during mid-season haul-outs.
- Replace corroded fixings, not just the anodes themselves.
7. Positioning anodes incorrectly on the hull.
The mistake:
Placing anodes in “shadowed” areas where water doesn’t flow freely reduces their effectiveness.
How to avoid it:
- Position anodes in areas with good water flow.
- For hull anodes, ensure they’re evenly spaced and not blocked by keels, strakes or other fittings.
- Follow manufacturer recommendations for shaft, rudder and trim tab anodes.
8. Not replacing anodes in time
The mistake:
Owners wait until the anode has disappeared completely before replacing it. By then, protection has already stopped, and damage may have started.
How to avoid it:
- Replace when an anode has eroded by 50% or more.
- Check anodes at every lift-out and mid-season inspection.
- Keep spares on board so you’re never caught short.
Final Thoughts
Sacrificial anodes are inexpensive compared to the damage they prevent - but only if they’re fitted correctly and checked regularly. By avoiding these common mistakes, you’ll extend the life of your boat’s metal fittings and save yourself costly repairs.
At Anode Outlet, we stock over 400 anodes in zinc, aluminium and magnesium, plus a huge range of anode accessories including bolts & fittings, electro eliminators and galvanic isolators. If you’re not sure which anode you need, our team is on hand to help - contact us today!
