Mystery hull issue - suggestions?

[George Braun]

2008 Hunter 36. Glass beaded, new barrier coat, new semi-hard bottom paint in spring 2024. Was a beatiful job done by our yard. Getting ready to get boat in the water for 2026 and have a mystery. pictures are of small raised spots that appear as "rust" on the keel. Categorically are not blisters.

Possible causes? Could a 2025 lightning strike in or near our marina be the cause? One boat had electronics fried entirely, we apparently lost a VHF. Could the havoc of a strike have caused a new stray current issue? Other than the spots, bottom is great, loving the semi-hard paint (Sea Hawk)

 

[Davidasailor26]

Looks to me like spots where the barrier coat has failed and the keel is rusting a bit. Rust is less dense than the iron so it bubbles out. Structurally it’s probably not any harm. If you want the keel to be fair you’ll need to sand or grind those spots back down to fresh metal, apply a new barrier coat, and paint.

 

[PaulK]

Are they on both sides of the keel? Saw something similar once with "bubbles" of antifouling paint that burst when poked and let out fine rusty iron filings. It was only on one side of the keel, which made us suspect a slip neighbor with faulty grouding causing a current in the water.

 

[Will Gilmore]

Glass beaded, new barrier coat, new semi-hard bottom paint in spring 2024. Was a beatiful job done by our yard. Getting ready to get boat in the water for 2026

How much time between when you last saw that "beatiful job done by our yard" in 2024, and "Getting ready to get boat in the water for 2026"? Is that damage overnight or over a season in the water? She was "beautiful" when she went on the hard?

If that happened on the hard, and not in the water, maybe lightning is a possibility. There is a distinct discoloration that appears to flash upward from the gravel that those spots are within.

-Will

 

[shemandr]

My 2002 H356 had a lead keel. This 2008 H36 appears to have iron or maybe steel.
Lightning or not, the remedy is to strip to bare metal and re-do coatings. The question is who will pay. I think it will be a hard sell to get the insurance to pay based on the lightning strike. But worth a shot. I think it's more likely the yard pooched the job with respect to the keel. Was the OP present when the barrier coat was applied to the keel? How long was it between stripping the keel and applying the barrier coat? And isn't pro forma to apply epoxy directly to the keel prior to a barrier coat? My experience with yard workers suggests that they did the keel the same as the hull. Except that the bottom is fiberglass and the keel is iron or steel.

 

[American_Mainsail]

I agree generally what most others are saying here. This seems to be a barrier coat issue and you have some light surface rust forming on the keel. It's very common with iron keels and I would say I see something approximating this on 1/2 of the iron keels I see at the yard.

I don't think you have an emergency on your hands, especially if you haul out every season. To remedy this you're looking at stripping down the antifouling and applying an epoxy modified barrier coat.

Since you recently had a lightning strike, I would definitely do a quick stray current test once the boat is back in the water to rule out issues in that department. I would particularly focus on unswitched loads, the bilge pump being the primary suspect.

Edit: After looking another time, you can very clearly make out the joint between the bottom bulb and the rest of the keel. This would tend to suggest to me that this area wasn't encapsulated with a barrier coat when they painted it. I can see this being overlooked by a yard crew that's just running through the yard during the preseason slapping paint on every boat off a list; but I don't know the specific situation here, of course.

 

[Davidasailor26]

My experience with yard workers suggests that they did the keel the same as the hull.

This is a pretty good guess. They (or a separate contractor) probably did the blasting, then some time later came back and applied the barrier coat. That’s fine for the fiberglass parts because they can sit indefinitely between the blasting and barrier stages. But in the meantime a layer of oxidation probably formed on the iron that’s led to loss of some adhesion. The barrier coat should really be applied in less than an hour after sanding to shiny metal.

 

[Barnacle Bill]

It looks like that is a cast iron keel and so needs to be cleaned very well and coated with a proper primer before applying antifouling. If there is any ferrous oxide (rust) on the keel, that could be an adhesion problem for paints. It is an ongoing issue with steel keels and you shouldn't be alarmed about it as it mostly is a cosmetic issue rather than the keel failing, etc. Paint it with the correct products and you should be fine.