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Sandy/crystalline substance around keel bolt

Nov 26, 2012
Hunter 34 Berkeley
So, this happened yesterday. I opened the keel bolt access hatch in the floor of my 1984 Hunter 34 and discovered this light grey sandy/ crystalline stuff around the aft keel bolt. The bolt itself appears in good condition but what is this stuff? Is it a by-product of corrosion or did it just settle here? Anyone else seen this? I sail SF Bay. No sandy beaches around here.


Sep 25, 2008
Alden 50 Sarasota, Florida
To state the obvious, the bolt and nut don’t appear corroded. The only other explanation is salt collected after evaporation.
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Apr 22, 2011
Hunter 27 Pecan Grove, Oriental, NC
The other two posters are probably right. But it is difficult to see crevice corrosion that is hidden inside the keel bolt nut, as you can see
in this shot on my boat. The gray is where the nut was. The white powdery area is where the washer was. Two of the bolts broke while being torqued. They looked fine from above except for some rust stains. I don't see any tell-tell rust stains in your pics.
May 27, 2004
Hunter 30_74-83 Ponce Inlet FL
Does it taste salty?
Put the material in warm water and see if it dissolves.
If not, is the bolt/nut in pic #1 at the lowest point in your bilge?
If you have a wet bilge, as I do, stuff migrates from all over, to the bilge
and settles at a low point.
Are your batteries in boxes or exposed?
No sandy beaches? How about wind blown dust, gravel parking lot residue,
cat litter???
Seriously though, your pic #2 seems to show a granular substance that
is too coarse to be galvanic corrosion dust. But I can't be sure from a pic.
Oct 22, 2014
CAL 35 Cruiser moored EVERETT WA
Salt is a possibility. There used to be salt manufacturing in the South Bay by Mortons. Every couple of years they would gather the salt and create a giant mountain of salt you could see the mountain from the interstate.
Nov 26, 2012
Hunter 34 Berkeley
Well, we recently took a trip up the delta where we sailed past a sugar factory near Benicia. I will put some of it on my cereal and let you know how it is.
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