What Are Hull Sides?
The hull sides of a vessel are more than just the skin that keeps the water out, they are critical structural components that provide stiffness and impact resistance. When moisture becomes trapped within the laminate or core of the hull sides, it can lead to costly delamination and significant structural weakness.
"Hull sides" typically refer to the vertical or near-vertical sections of the hull that rise from the chine (where the bottom meets the side) up to the gunwale (the top edge of the hull).
While the hull bottom supports the boat's weight and handles slamming loads, the hull sides provide longitudinal stiffness and protect the vessel from side impacts and docking stresses.
In modern fiberglass boat building, hull sides are often constructed using cored laminate technology. This involves sandwiching a lightweight core material (such as balsa wood or structural foam) between two layers of fiberglass. This "sandwich" construction creates a panel that is incredibly stiff and light, but susceptible to moisture if the outer skin is breached.
What Are Wet Hull Sides?
"Wet hull sides" describes a condition where water has migrated into the fiberglass laminate or, more commonly, into the core material itself.
This isn't usually a pool of standing water. Instead, moisture moves through capillary action, wicking through the fibers of the glass or the cells of the core material. Once inside, the water is trapped between the impermeable fiberglass skins, unable to evaporate naturally.
Crucial Distinction
Wet does not always mean delaminated. A wet hull side has high moisture content, but the bond between the core and the fiberglass skin may still be intact. If caught at this stage, the structure can often be dried and saved without invasive surgery.
How Do Hull Sides Get Wet?
Water intrusion in hull sides is often gradual and invisible. Common pathways include:
- Through-Hull Fittings: Vents, drains, and exhaust ports penetrate the core. If the core isn't sealed ("decored") around these holes, water seeps directly in.
- Deck Hardware: Rail bases, cleats, and stanchions mounted near the gunwale can leak, allowing water to trickle down inside the laminate.
- Window & Portlight Bedding: Seals around windows degrade over time, creating a direct path for rainwater and spray into the hull structure.
- Rub Rail Damage: Impacts at the dock can crack the gelcoat behind the rub rail, letting water in during washdowns or rain.
Why Wet Hull Sides Are a Serious Structural Issue
Ignoring moisture in hull sides can lead to cascading failures:
- Reduced Stiffness: A wet core loses its compressive strength and shear properties. The hull side becomes flexible, potentially causing "oil-canning" or buckling under load.
- Freeze/Thaw Damage: In cold climates, trapped water expands when it freezes. This hydraulic pressure forces the fiberglass skin away from the core, causing immediate delamination.
- Rot & Degradation: Balsa cores will rot and turn to mush. Foam cores, while rot-resistant, can still suffer from hydraulic erosion and freeze damage.
- Resale Impact: High moisture readings on the hull sides are a major red flag for surveyors and can make a vessel unsellable or uninsurable.
Wet Hull Sides vs. Hull Side Delamination
Understanding the difference between wet and delaminated is critical:
Wet Hull Sides
- High meter readings
- No visible bulging
- "Tap test" sounds solid/dull
Can be Dried & Saved
Delamination
- Visible blisters or bulges
- "Tap test" sounds hollow/sharp
- Structural integrity lost
Can be fixed depending on extent
Concerned About Wet Hull Sides?
Review your findings with our team before committing to expensive surgery. We can help you understand your options.
Signs of Wet Hull Sides
While a moisture meter is the definitive tool, other signs can indicate trouble:
- Softness or Flexing: If you press on the hull side and it flexes easily, the core may be compromised.
- Weeping or Staining: Brown stains running down from fittings often indicate rusty water escaping from a wet core.
- Musty Odor: A persistent smell of dampness in cabin lockers or storage areas along the hull.
- Stress Cracks: "Spider web" cracks in the gelcoat can be a symptom of a hull side that is flexing too much due to a soft core.
Note
Moisture can be present deep in the core even without these obvious cosmetic symptoms.
The Traditional Repair Approach
Historically, fixing wet hull sides meant major surgery. Boat yards would cut away large sections of the exterior or interior fiberglass skin, scrape out the wet core, and rebuild the laminate layer by layer.
This approach is effective but comes with significant downsides: high cost, long downtime, potential cosmetic matching issues, and the risk of altering the boat's factory structure.
A Non-Invasive Restoration Approach
Dryboat International® offers a multi-patented, non-invasive alternative.
By drilling small micro-ports into the affected area, we can inject warm, dry air to circulate through the core material. This targeted airflow extracts moisture at the molecular level, returning the core to dry, structural standards without the need for large-scale tear-out.
This process preserves the original fiberglass skin and structural integrity. In many cases, it can even be performed while the vessel remains in the water or during winter storage, minimizing downtime.
When Wet Hull Sides Should Be Addressed
Time is not on your side. Wet cores rarely dry out on their own; they tend to get wetter and spread over time.
Recommended Next Steps:
- 1
Document the Area
- Take photos and note the location of high moisture readings.
- 2
Confirm Scope
- Get a qualified evaluation to determine if delamination has occurred yet.
- 3
Choose Preservation
- If the skin is still bonded, opt for the least invasive solution that protects your hull's structure and value.
Get a Professional Assessment
Dryboat International® works with owners worldwide to plan non-invasive moisture removal.
Common Questions
- Can you dry balsa core? Yes.
- Is painting required after? Usually minor touch-up only.
- Does moisture spread? Yes, over time.
