Aluminum anodes, been reading they are better than zinc?

example
When to Use Zinc Anodes or Aluminum Anodes on Your Boat

 

I say go for it... but its zinc for me in salt water.

My refrigeration system is my highest zinc wear item, about the same cost as my main. Due to multiple metals involved and the near constant daily flow of turbulence sea water its prime for zinc wear. Its still probably the cheapest part of the yearly operation for the zinc, its probably less than a tenth of a percent of operation on my system let alone my entire boat.

 

A learning time for me, I already have the zinc pencils, but maybe next time will go for aluminum.
Be nice to get longer life. What typically happens, I let them go longer than I should. By the time I get to it, there is nothing left and I have to dig the stump out of the brass plug.

Yet all the HE have continued to function and not leak.

I am interested in rudder, shaft, trim tab aluminum zincs, if they really do last longer.
Example, they have my shaft size, 1 3/8", and price seems good.

Seems few here have experience with aluminum anodes.

Shaft Aluminum Anodes | BoatZincs.com

 

Martyr Aluminum anodes are military spec.
Says they last 50% longer than zinc and protect better in brackish and salt than zinc.

 

Nigel Calder says use aluminum anodes ff you can, they last a lot longer, they are preferred over zinc.

 

MSN https://www.msn.com/en-us/weather/topstories/beaching-a-45-foot-boat-for-the-first-time-in-unfamiliar-waters/vi-AA1J77i4?ocid=msedgntp

 

I just looked at my anodes I had bought years ago for this haulout, and they are aluminum. Rudders, shafts and 4 for the trim tabs.

 

This time I am going with Aluminum anodes instead of zinc anodes. I heard they can last longer in salt water and work bettter?

ChatGPT said:


Yes — you’re right. ⚓ Aluminum anodes are becoming the preferred choice over traditional zinc in saltwater (and even brackish water). Here’s why:

Aluminum vs Zinc Anodes
1. Driving voltage (electrochemical potential)

• Aluminum anodes produce a slightly higher driving voltage compared to zinc.
  
  
• That means they can protect manganese bronze props and shafts more effectively, especially when there’s marine growth or paint layers creating resistance.
  

2. Longer life

• Aluminum is lighter, so for the same block size, you get more usable anode material.
  
  
• Zinc anodes can form a hard “calcium sulfate” coating in warm salt water that stops them from working — aluminum anodes don’t have that problem.
  
  
• Aluminum anodes typically last 2–3 times longer than zinc in the same conditions.
  

3. Environmentally safer

• Zinc anodes often contain cadmium, which is toxic.
  
  
• Aluminum anodes are cadmium-free and generally considered more eco-friendly.
  

4. Versatility

• Zinc → works only in salt water (they can go passive in brackish/fresh).
  
  
• Magnesium → only for fresh water (too active for salt, they’ll “burn up”).
  
  
• Aluminum → works in all three: fresh, brackish, and salt water. That’s why the U.S. Navy shifted to aluminum alloys for ships decades ago.
  

Any downsides?

• They cost a little more up front than zinc.
  
  
• If you have mixed old and new anodes (zinc + aluminum), they can work against each other — so it’s best to switch everything over to aluminum at once.
  

✅ For your manganese bronze Michigan Wheel props on a 1.375" shaft, aluminum shaft anodes and hull anodes will give better, longer, and more consistent protection than zinc.

Do you want me to give you the ideal shaft anode size and number for your 1.375" shaft and 22×20 prop setup (so you’re not under- or over-protected)?

 

I've owned a Marinette aluminum cruiser for many years. Marinette specifies a special alloy of aluminum for hull protection, that they sell in strips that you cut to length to bolt to keel and the trim tabs.I've forgetten the trade name for it - Alumalloy or something like that.

 

I found out Aluminum anodes are doped with Indium and Tin, that keeps the metal active to prove anode protection.
I am also going to smear coat the underwater metals with AirTec Seaguard SG-145 grease, it should stay on hopefully between hauls.
Maybe get 2 years from that grease.
I had about 5 diferrent choices for greases for underwater use. This one I will try.
AirTec Grease: SG-145 SeaGuard Marine Grade Grease – AET Systems


The Best Greases for Marine Applications %%page%% %%sep%% %%sitename%% – AET Systems
The best marine grade grease is AirTec SG145 SeaGuard. Seaguard is rated for both salt and fresh water and is designed for extreme duty in the most intense marine applications. Let’s check the test data:

• Thickener: Calcium
• Base oil: Mineral
• Base oil viscosity: 145 cSt at 40 degrees Celsius
• NLGI Grade: 2
• 4-Ball-Weld Load: 620 kgf
• Texture: Extremely Tacky
• Color: Black (designed to be easily identified so you know when the grease is there or not)

SeaGuard is rated for use in boats, boat trailers, barges, underwater construction machines, crane, davit crane, exploratory drilling machines, dam gates, winches, and cables. This grease is designed to protect against corrosion caused by salt and fresh water, more importantly it also functions perfectly in dry applications so you don’t have to worry about it dry out when your boat or trailer is out of the water.

 

A ChatGPT link to greasing your underwater metals.
Idea is to help limit both marine growth and corrosion for longer than just basically nothing but anodes between hauls.
I had another conversation and I have more grease candidates than these, apparently there are some greases designed to stay on underwater more than you might think.

ChatGPT - Marine aluminum greases https://chatgpt.com/share/68aef0b2-9cd0-8010-9a09-5214f6b39018

And here is one that could be good, says very hard to remove, it is made with copper powder.
Waterproof Open Gear Lubricant | Open Gear Grease | Superior Industries, Inc.
Temperature Range: -20°F (-29°C) to 500°F (260°C)

Water Proof: For Under Water Use

High Pressures: Up To 150,000 PSI

NLGI Grade: 2

Worked Penetration: 265-295

Compound: Synthetic Open Gear Grease

USDA Rating: H-2



Bronze Plate takes first place among open gear lubricants for its tackiness, resistance to extreme environments, and tenacious fill qualities. This waterproof open gear lubricant provides outstanding lubrication to gears and machinery, wet or dry, and will successfully coat couplings, gears, and cables underwater. Salt water, chemicals, high temperatures, and high pressures will not affect its incredibly thick, sticky nature.

Bronze Plate is the top choice for industrial, marine, and mining machinery utilizing open gears and draglines. In addition, Bronze Plate incorporates bronze and copper particles into its synthetic grease to fill pits and crevices, giving you quieter, more uniform - and more efficient - gear teeth.

 

My other discussion about Marine greases underwater with a goal of staying on 2 years
ChatGPT - Wash off underwater compound https://chatgpt.com/share/68ab7de1-9798-8010-ac86-f26a7b43beeb