25 yrs boat ownership, bottom paint on struts-props fails, going with zinc galvanized paint

[sdowney717]

Specifically Rust oleum in a spray can.
Some said on forums worked as good as prop speed.
Lasted 2 years.

20 oz Rust-Oleum 7585838 Cold Gray Professional Galvanizing Compound Spray - Cold Galvanize Spray Cans - Amazon.com

 

[kapnD]

You’ll get a much more effective coating by brushing on thick rather than spraying.
Works fairly well on bronze, not as well on Stainless.
YRMV depending on local conditions.

 

[sdowney717]

You’ll get a much more effective coating by brushing on thick rather than spraying.
Works fairly well on bronze, not as well on Stainless.
YRMV depending on local conditions.

That boat forum said 3 coats and he gets 2 years in south Florida waters
I did look into a quart of high zinc paint

 

[kapnD]

A big factor in longevity of any antifouling coating is how well it is applied, and how often the boat is used.
Boats that are under way on a daily basis fare far better than those that sit at the dock for extended periods.
I’m currently testing a thick layer of brushed on galvanizing coating on propeller and strut.
Water temps ranging from 78*-81*F , boat is run once or twice a week.
Slime grows on it at a similar rate to untreated bronze, but barnacles seem to be slower to develop.
I’ve been scraping the running gear clean of slime and small barnacles about once a month, and I fear I may have already removed much of the zinc along with the growth, as it is not a very hard coating.
At this point, I’m calling the results as better than nothing, better than ablative bottom paint, and about equal to hard bottom paint.

 

[sdowney717]

A big factor in longevity of any antifouling coating is how well it is applied, and how often the boat is used.
Boats that are under way on a daily basis fare far better than those that sit at the dock for extended periods.
I’m currently testing a thick layer of brushed on galvanizing coating on propeller and strut.
Water temps ranging from 78*-81*F , boat is run once or twice a week.
Slime grows on it at a similar rate to untreated bronze, but barnacles seem to be slower to develop.
I’ve been scraping the running gear clean of slime and small barnacles about once a month, and I fear I may have already removed much of the zinc along with the growth, as it is not a very hard coating.
At this point, I’m calling the results as better than nothing, better than ablative bottom paint, and about equal to hard bottom paint.

Yes, I imagine the coating is soft. And scraping on it removes some of this paint.

And the price is a lot less for the zinc paint, if you use the spray can
In my case for under $10, if it slows down the barnacles on the running gear even for a year, it's worth doing.

Every time after painting bottom paint on running gear, hauls show zero paint on them.
Not even a little is left. Maybe there is an electrochemical metal reaction the loosens the paint off the metal.

My boat is 55 years old in Chesapeake lower bay water, so it's salt water, likely it's entire life. And the running gear still looks good.

I have seen prop speed, it is a liquid silicone copper colored rubber paint.
I have wondered if using Permatex copper RTV silicone gasket maker, smearing on a coating by fingers would help.
It is waterproof, sticks on metal good, but it cant really be scraped like with a knife. It can be scrubbed with a soft brush. not a wire brush.

example
Permatex Ultra Copper RTV Silicone High Temperature Gasket Maker 3 oz

 

[sdowney717]

Got more confirmation. Talking to an older Chesapeake Bay deadrise owner and boat painter. He used to use copper paint on the running gear, which also never worked. The solution he was told by others is use the zinc spray paint. He is painting a 47 foot deadrise, and I see the underwater metal he has it clean and shiny. I ask him is he going to put bottom paint on the running gear, and nope, he is not, they don't do that, they use the zinc paint.

Now I was thinking why not also grease it up after painting zinc. I have been using lots of this Oatey white teflon pipe dope grease, and that stuff is very sticky and waterproof.
I used it yesterday smeared on the bronze strut bolts as a sealer. Then on the the inside on the bronze washers and nuts. On my boat those bolts are double nutted, so they won't come loose from that grease.

Could be easily smeared on as a thin layer. If not the prop, then the prop struts, prop shafts, tabs, rudders maybe. But I would try it on everything.
Here in the US, Lowes has it cheap enough.
It will wash off with soap, but it repels water, and is thicker than grease.
If it lasts a while it is a help. And I think it may embed into the zinc paint which is somewhat rough or porous as it is a primer.

Oatey® Great White® Pipe Joint Compound With PTFE | Oatey

 

[kapnD]

Lanolin grease is the old school go to for an oily coating on underwater metals.
It’s real sticky, but wears off pretty quickly depending on the speed of operation, water temp.
Effectiveness goes away quickly, hardly worth the effort except maybe as a preservative if the boat is not going to move for a while.
I don’t think that the Teflon will fare any better, unless you can find a way to bond it to the metal.
A sacrificial coating does have merit, but the uneven pressures on various parts of the propeller make it complicated.
Food for thought— I used to ride some motocross, and had goggles that were covered with multiple layers of thin clear plastic that could be easily peeled off as they became too dirty.

 

[sdowney717]

I was sort of thinking this oatey pipe sealer is very water proof stuff. It is made to not wash away with water. It certainly does not wash off my hands unless I use soap.

Lanolin might be bio degrading?

The thing about what makes primer good for painting top coats is it has a porous nature. It absorbs the top coat to make a better bond.
That galvanized zinc paint is a primer kind of paint.
I got a sense that will work too with this Oatey pipe sealer. It is worth a try. It certainly wont hurt anything.

 

[kapnD]

Teflon paste is a thread sealer, not pipe sealer. It is not designed for exposure, and will wash away quickly.

 

[sdowney717]

Idea is smear on a long lasting underwater grease to protect between haulouts that does not cost an arm and a leg!
Aiming for 24 months.
Coat prop, prop shaft, shaft struts and trim tabs.

My thinking is paint them with the zinc paint, them smear on a coat of underwater grease.

 

[kapnD]

Don’t know if it’s available anymore, but there used to be a product called Cosmoline, a very thick, waxy grease that was designed to preserve metals for shipping and storage.

 

[sdowney717]

Don’t know if it’s available anymore, but there used to be a product called Cosmoline, a very thick, waxy grease that was designed to preserve metals for shipping and storage.

it is, but chatgpt says it will come off underwater

Here is a shared link to a full discussion I had about various greases
ChatGPT - Wash off underwater compound https://chatgpt.com/share/68ab7de1-9798-8010-ac86-f26a7b43beeb
would Cosmoline stay on underwater in salt water

ChatGPT said:


Good question. Cosmoline is a classic long-term metal preservative — basically a very waxy, greasy, petroleum-based corrosion inhibitor. Here’s how it behaves in your situation:

Strengths of Cosmoline

• Extremely good corrosion resistance in air – It’s designed to keep stored machinery, firearms, and ship parts rust-free for years.
  
  
• Waxy, tacky film – Once applied, it hardens into a greasy wax that resists handling and splash water.
  
  
• Very long service life in dry storage – Decades, if undisturbed.

Limitations Underwater

• Not designed for full immersion – Cosmoline is intended for storage and transport, not constant submersion.
  
  
• Salt water exposure – In immersion, especially moving salt water, the film will soften and gradually erode, especially at edges. It won’t “wash off instantly” like pipe dope, but it won’t last 24 months underwater.
  
  
• Marine use cases – Navies and shipyards used Cosmoline on spare parts stored onboard, but not on working underwater gear like props or shafts.

Comparison

• Cosmoline = excellent for above-water, splash zones, storage.
  
  
• Calcium sulfonate marine greases or lanolin-based coatings = far superior for continuous underwater exposure.
  
  
• Some lanolin coatings (like Lanocote or Lanolene) are specifically marketed for props, shafts, and trim tabs, because they don’t wash off nearly as easily and are more eco-friendly.

Bottom line: Cosmoline will stick for a while underwater, especially in calm water, but in real-world saltwater immersion it won’t reliably last until the next haul-out. If you want something to stay 12–24 months on props, shafts, and trim tabs, a calcium sulfonate marine grease or a lanolin-based product is a better bet.

Do you want me to give you a shortlist of products that actually outperform Cosmoline underwater on running gear?


You said:
yes

ChatGPT said:
Here’s a refined list of greases and coatings that outperform Cosmoline for props, prop shafts, and trim tabs, aimed at lasting up to 24 months underwater:

Top Long-Lasting Grease Options for Underwater Use
1. Quicksilver 2-4-C Marine Grease (Lithium-Based)

• Overview: A versatile lithium-based grease that resists degradation when mixed with water—ideal for marine applications like prop shafts.
  
  
• Applications: Used on prop shaft splines, steering system components, drive shaft splines, and more quicksilver-products.compropshopinc.com.
  
  
• User Feedback: Praised for staying effective and preventing prop seizure even under saltwater exposure.
  
  
• Product Availability:

Versatile, OEM marine standard
Quicksilver 2‑4‑C Marine Grease

$20.00
Outboard Parts Online + others

★★
4.9

Enhanced with PTFE for extra protection
Quicksilver 2‑4‑C with PTFE

$24.27
Modern Boat Sales & Service

ChatGPT chooses products independently. Learn more
2. Lucas Marine Grease (Over-Based Calcium Sulfonate)

• Advantages: Exceptionally tacky, designed for marine conditions with high adhesion and corrosion protection. Boasts a weld load rating of 500 kg and resists wash-off effectively lucasoil.com.
  
  
• Why It’s Good: Its adhesive, long-lasting properties make it a top choice for submerged parts.

3. AirTec SG-145 SeaGuard (Calcium-Thickened)

• Standout Features: Calcium-based thickener, very tacky, performs under extreme pressure (4-ball weld load: 620 kg), formulated for both salt and fresh water environments AET Systems.
  
  
• Ideal For: High-stick, long-retention situations—perfect for prop shafts and trim tabs in harsh marine conditions.

4. Lanolene™ (Lanolin-Based Coating)

• Application & Performance: Forms a waxy anti-fouling barrier. Typical durations:
  • Low-use boats: 2–3 months
    
    
  • Medium-use: ~6 months
    
    
  • Heavy usage: up to ~12 months lanolene.com+1.
• Real-World Insight: Aboaters report lanolin lasting well (though not always full season):
  
  “Lanolin worked very well for me... after about 8 weeks I dried out the boat and re-applied as it had thinned out somewhat...” YBW Forum
  “I have used Lanocote… lasts about 5 or 6 months.” CruisersForum

Side Notes: Aluminum Complex & Specialty Greases

• Aluminum Complex Greases: Products like Schaeffer’s #274 are highly waterproof and offer excellent saltwater resistance Bob Is The Oil Guy.
  
  
• Calcium Sulfonate Compatibility: These remain compatible with lithium greases and offer better corrosion and water resistance Boating Forum - iboats Boating ForumsReddit.

Product Recommendations

Versatile, OEM marine standard
Quicksilver 2‑4‑C Marine Grease

$20.00
Outboard Parts Online + others

★★
4.9

Enhanced with PTFE for extra protection
Quicksilver 2‑4‑C with PTFE

$24.27
Modern Boat Sales & Service

• Quicksilver 2‑4‑C Marine Grease — Reliable, broadly used marine-grade lithium grease. Highly water-resistant and ideal for prop shafts and linkages.
  
  
• Quicksilver 2‑4‑C with PTFE — Same trusted grease formulation enhanced with PTFE—a great extra layer against wear and corrosion.

Quick Reference Table
Product / Type Best Feature Estimated Duration Underwater
Quicksilver 2-4-C (Base) OEM standard, durable, water-resistant Seasonal to multi-season (with reapply)
Quicksilver 2-4-C + PTFE Added wear/corrosion protection Extended durability over base
Lucas Marine Grease Highly tacky, excellent adhesion and corrosion protection Long-lasting marine-grade performance
AirTec SG-145 SeaGuard Extremely sticky, heavy-duty, extreme condition use Superior adhesion and retention
Lanolene™ (lanolin-based) Anti-fouling wax, eco-friendly ~5–12 months depending on usage
Aluminum Complex (e.g., Schaeffer #274) Water- and salt-resistant, waterproof High resistance, possibly long till next haul-out
Final Take
For props, prop shafts, and trim tabs aiming for 24-month durability underwater:

• Go with a high-performance calcium sulfonate or lithium-based marine grease, such as Lucas Marine Grease or Quicksilver 2-4-C (with PTFE for added durability).
  
  
• If extreme adhesion and long-term retention are priorities, AirTec SG-145 SeaGuard is an excellent choice.
  
  
• Use Lanolene™ as a supplementary anti-fouling wax layer—especially useful if you need occasional reapplication between haul-outs.

Let me know if you'd like help sourcing these locally or checking detailed specifications!

 

[sdowney717]

This grease would likely work very well long term underwater, says it is very hard to remove.
Waterproof Open Gear Lubricant | Open Gear Grease | Superior Industries, Inc.

This grease also looks interesting.
Would have to scrape it out of the tube to apply
AirTec Grease: SG-145 SeaGuard Marine Grade Grease – AET Systems

Typical cartridge grease choices below
Amazon.com: Quicksilver 802863Q1 2-4-C Marine Grease/Lubricant with PTFE - 14 Oz. Cartridge : Automotive

Maybe this too
Schaeffer 274 Moly EP Synthetic Plus Waterproof Grease, Tube

Cheapest one
Lucas Oil Products Marine Grease: Premium Heavy Duty Lithium Complex Grease, 14 oz. 10320 - Advance Auto Parts

Out of them all, the first would be best.
But maybe the Airtec as it is less costly versus the first one.

I have long term automotive experience, worked on cars-trucks for decades. But underwater use of marine grease, I have little experience.

 

[sdowney717]

Neighbor's deadrise at my marina , rudder and prop painted with zinc spray paint made by SeaHawk
The deadrise is maybe 47 footer and is no longer fished.
The framework is for a canopy cover.

My boat is foreground far left in pic show part of the hull

 

[sdowney717]

zoomed in.
Paint feels a little harder and has a slight shine compared with the Rustoeleum
They painted the zinc anode. I wonder about that.