Narrowing or hourglassing at the waterline
Marine borers — gribble (Limnoria) — have eaten the outer wood in the splash zone, reducing the cross-section that carries load.
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Is my dock failing?
Most dock failure announces itself months before it becomes dangerous. Here is what to look for, what each symptom actually indicates, and how urgent it is.
How can I tell if my dock is unsafe?
A dock is unsafe when it moves under a single person's weight, when a piling has lost visible cross-section at the waterline, or when soil is escaping behind a bulkhead. Any of those three means stop using the structure and have it assessed before the next high tide.
Last updated: August 2026
Pilings
The dock moves underfoot when nobody else is on it
One or more pilings have lost fixity in the mud, or the connection between piling and framing has failed.
Stop using it
Sound wood outside, hollow when struck
Teredo shipworm tunnels from the inside out. The surface stays intact while the interior is consumed — this is the failure mode you cannot see.
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Decking
Boards cupping upward at the edges
Repeated wet-dry cycling from tide and salt spray. Cupping holds water on the board and accelerates the next stage.
Plan repair
Fastener heads standing proud of the board
The wood has moved around the fastener through enough cycles that it no longer holds. A trip hazard first, a structural issue later.
Plan repair
Soft spots at the joist line
Water is sitting in the joint between deck board and framing. The framing underneath is usually further gone than the board on top.
Assess now
Boat lift
One side rises faster than the other
A stretched or corroded cable, a slipping drum, or a lift piling that has moved. Running it racked damages both the cradle and the boat.
Stop using it
Rust bleed at cable terminations
Galvanic corrosion where dissimilar metals meet in brackish water. The visible bleed usually understates the section loss inside the fitting.
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Bulkhead
The wall is leaning toward the water
Tie-backs anchoring the wall to the deadmen behind it have failed, or the soil holding those anchors has washed out.
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Sinkholes or depressions in the lawn behind it
Soil is escaping through the wall. The void behind the bulkhead is larger than what shows at the surface.
Stop using it
Found something on this list?
Photograph it before anything is moved, then call. A photograph of the symptom is usually enough to say whether it needs a site visit this week or this season.