Wooden Boat Annual Hull Survey & Below-Waterline Condition Log

ContextWalk the hull before the pressure washer starts. Soft spots, discolored anti-fouling, and marine growth concentrations are easiest to identify on a wet hull straight out of the water. Mark each suspect area with a numbered chalk circle — the numbers correlate to your diagram later. Pressure washing removes surface evidence permanently; marking first means your initial observations are not lost. Pay particular attention to areas flanking through-hulls, near keel bolt locations, and at any previously repaired sections.

ContextA wet hull surface reveals plank edge grain, check-cracks, and soft spots far more clearly than a dry one. Soft, waterlogged wood appears distinctly darker and may show a slight surface depression. Discolored streaks — orange, brown, or black running from fastening holes — indicate corrosion bleeding through. Note any areas where anti-fouling paint has lifted, blistered, or delaminated as locations for closer follow-up. Complete your first visual pass before the hull begins to dry; the window is roughly 30–60 minutes on a warm day.

ContextKeel and garboard areas require you to work beneath the boat, flat on your back if necessary. A high-output LED shop light or a good headlamp is non-negotiable; natural light at an oblique angle is also excellent for spotting surface irregularities and surface depressions. If the boat is above eye level on stands, use scaffolding or a stable ladder rated for the task. Rushing a survey because you cannot see properly, or cannot comfortably reach the keel area, is how serious problems get missed year after year.

ContextA survey or planking hammer has a brass or lead head weighing 12–16 oz, sized to transmit vibration into the plank rather than simply making surface noise. Work in overlapping rows, tapping each plank every 6–8 inches along its length. A solid plank returns a clean, slightly ringing tone. A soft or waterlogged plank returns a dull thud — sometimes described as hitting a pillow — or a dead, flat non-resonant sound. Pay extra attention to the sheer strake at the waterline, the garboard plank adjacent to the keel, and any planks surrounding through-hulls or previous repair areas. Mark every dull-sounding location with chalk for follow-up probing.

ContextAfter sounding, follow up every marked location with firm, deliberate pressure from a sharp pick. Healthy wood resists penetration — you should need real effort to sink the pick even a millimeter into sound plank face. Wood that compresses easily, springs back spongy, or allows the pick to enter without meaningful resistance is rot-compromised. Distinguish between surface softness — top 2–3mm, often treatable with epoxy consolidant — and through-softness, where the pick enters freely, indicating advanced decay requiring plank replacement. Do not confuse end-grain softness at butt joints with mid-plank decay; end grain always feels softer and requires a different evaluation. Document the approximate depth of pick penetration at every suspect spot.

ContextOrange-brown staining streaming downward from a fastening hole is a clear sign of iron or galvanized fastener corrosion. The stain itself is a secondary concern; the primary issue is that corroding iron expands as it oxidizes, eventually splitting the plank from inside — a condition called nail sickness. Black staining in oak planking at fastening locations is tannin reacting with iron, which is distinct from rot but marks every iron fastener on the boat. A hull fastened with iron cut nails or early galvanized screws is on a fundamentally different maintenance timeline than one fastened with silicon bronze, and the presence of staining is your signal to examine fastening condition more closely.

ContextA pin-type or pinless moisture meter set to the correct wood species profile gives you quantitative data rather than tactile impression alone. Readings below 19% moisture content are generally acceptable for planked hull wood; above this threshold, rot organisms find progressively more favorable conditions. Readings of 25–35% indicate persistent saturation; above 35% is actively waterlogged and should be investigated for a source. Take readings at the same fixed reference points each year — document them on your hull diagram — so you can track trends. Moisture meters measure moisture content, not structural integrity, and must be used alongside sounding and probing rather than as a standalone tool. A dry-reading area can still have historical rot damage; a wet-reading area may simply be a benign pocket of retained moisture.

ContextIn carvel-planked hulls, below-waterline seams are backed with cotton caulking driven into the seam bevel, then covered with paying compound. Run a pick along every seam at intervals of roughly 12 inches. Cotton that has dried and compressed to near-nothing, or that can be teased free with light pick pressure, has lost its mechanical backing and will not hold compound regardless of how it is painted. A seam without adequate backing cotton is a seam waiting to open under immersion pressure. Pay particular attention to seams near the keel where working loads concentrate.

ContextSeam compound — typically a polysulfide or polyurethane sealant in modern practice — serves as the watertight skin over the caulking backing, not a structural seal. It should be continuous, slightly proud of the plank surface, and fully adhered on both edges. Fine hairline cracks running along the center of the compound bead are normal surface shrinkage and can be re-topped. Cracks opening at the plank edges, or compound peeling away from one or both plank faces, indicate the seam has moved due to plank swelling stress, drying shrinkage, or fastening failure beneath. Open seams wider than 2mm need re-caulking, not just re-topping. Photograph every open seam with a ruler for scale and record location on your diagram.

ContextBelow-waterline seam widths should be roughly consistent along each plank's length — typically 1–3mm for a well-maintained carvel hull. A seam that is properly closed amidships but gaping near the keel or stern indicates plank edge movement, sometimes caused by fastening failure or frame distortion beneath the plank. Conversely, uniformly tight seams with no visible compound can mean planks have swollen so firmly against each other that they are compression-loaded — which causes checking along the grain if the boat dries rapidly on the hard. Both conditions are worth noting and tracking year to year.

ContextThe garboard plank runs along either side of the keel rabbet from stem to stern — it is the most water-exposed, most fastening-stressed, and most frequently decayed plank on a wooden hull. The garboard seam, between the garboard plank and the keel rabbet, is also the most difficult to caulk well and the most likely to re-open after any plank movement. Devote at least 50% of your total seam inspection time to the garboard. A garboard seam that has opened more than 3–4mm needs professional re-caulking before launch; sailing on a weeping garboard seam means sailing with a below-waterline leak that will not close under pressure and progressively worsens with use.

ContextKeel bolts run from the ballast keel up through the deadwood and keel timber and are typically covered with wooden bungs at the bolt head. Any rust staining around a bung, or a bung that has lifted and no longer sits flush, indicates the bolt beneath is corroding and expanding. A raised ring of wood around the bung hole — where surrounding grain is slightly higher than the bung — confirms expansion pressure from ongoing oxidation. Most wooden boats have 6–12 keel bolts; each is a structural connection between ballast and hull. Pull bungs at the two or three most suspect locations annually and inspect bolt heads directly. Replacement of a single corroded keel bolt typically costs $300–$800 in a fitted wooden boat; discovering they are all failing simultaneously costs much more.

ContextThe deadwood comprises the structural timber assembly between the keel and hull — stem, keel, sternpost, and the various knee and apron timbers connecting them. On older vessels this is laminated from several pieces joined with bolts, drifts, or adhesive; delamination at any joint compromises both structural strength and watertightness. Feel for raised edges, step-offs between layers, or visible gaps at joint lines. A joint line filled with silt or black marine growth has been open underwater for some time. Probe joint lines directly with a pick — separation that allows the pick to enter 5mm or more without resistance is a finding requiring a boatwright's assessment.

ContextThe junction between a cast iron or lead ballast keel and the wooden hull structure is a persistent maintenance hotspot. Cast iron keels corrode and expand over decades, distorting the bolt pattern; lead keels are more dimensionally stable but cold-flow under sustained load. The joint requires a compressible bedding compound — polysulfide or a dedicated marine elastomeric sealant — that can accommodate minor movement. A weeping keel joint, visible as moisture, fresh orange staining, or a trickle during initial haul-out, needs to be properly re-bedded before launch. The materials cost $50–$150; deferring the repair for another season typically requires removing additional structure that has since been damaged by water intrusion, multiplying both time and expense.

ContextFastening material determines your failure mode and your maintenance timeline. Silicon bronze — reddish, no staining — is the gold standard, essentially immune to galvanic corrosion in a properly managed hull and capable of lasting 40–60 or more years. Copper behaves similarly. Galvanized steel produces rust streaking over time and has a realistic below-waterline service life of 15–25 years depending on coating integrity. Iron fastenings corrode rapidly in salt water. Stainless steel fastenings look excellent externally but suffer crevice corrosion when buried in wood without oxygen access — a bolt can appear intact at the bung and be severely wasted in the middle of the plank. If your fastening material is unknown, determine it before surveying; your maintenance expectations are completely different for each material type.

ContextPull one fastening from a highest-stress or suspect location — garboard plank, near a through-hull, or a plank that sounded dull — and one from a seemingly sound area as a control. Use a bung puller and the correct-sized screwdriver or socket; never an impact driver, which damages the wood surrounding the bung hole. A healthy silicon bronze screw shows a bright surface with full thread profile. Corrosion appears as pitting, shank thinning — sometimes dramatic, with a screw reduced to 40% of its original diameter while still holding in the wood — or a crumbling thread form. If sample fastenings from suspect areas show severe corrosion, budget for a full refastening project rather than localized repairs; the fastenings throughout the hull are almost certainly the same material and age.

ContextIron and galvanized fastenings, as they corrode, produce iron oxide that occupies significantly more volume than the original metal. This expansion acts as a wedge, splitting the plank along the fastening line — visible as a crack running parallel to the plank edge at precisely the depth of the fastening head. This condition is irreversible once established; affected planks must be replaced and re-fastened with non-ferrous hardware. If one plank shows this pattern, inspect all adjacent planks immediately — a boat fastened with iron throughout will show this progression across the hull, not in a single isolated location.

ContextEach seacock should open and close with moderate hand force — not stiff requiring tools, not loose enough to turn under vibration. Stiff operation in a ball valve or traditional cone-type seacock indicates corrosion or marine growth on the working surfaces. With the boat ashore, open each seacock fully, rotate it all the way back to closed, and confirm it seats completely. A seacock that cannot be fully closed is a potential sinking hazard. If a seacock has not been exercised in more than six months, do not force it; apply penetrating lubricant and attempt movement gradually. Seized seacocks are responsible for a disproportionate share of marina sinkings — they were fine until they were needed in an emergency.

ContextThrough-hull fittings penetrate the planking and create a potential water intrusion point at the flange-to-hull interface and at the backing block behind the hull. Sound the wood surrounding each fitting with your survey hammer and probe with a pick. Soft wood at a through-hull almost always means the backing block or surrounding planking has been saturated, often because the original bedding compound dried out and allowed a hairline weep for years. A through-hull fitting in soft wood must be removed, the degraded wood repaired or replaced, and the fitting re-bedded in fresh compound. Caught early this is a $200–$600 repair; a fitting that works loose underway creates an emergency.

ContextEvery hose attached to a seacock below the waterline should carry two stainless steel hose clamps, positioned so the second clamp does not overlap the first, with screw heads at offset angles for independent mechanical redundancy. Check clamp bands for rust streaking — stainless steel corrodes, particularly lower-grade alloys, and a corroded clamp band can snap without warning. Ensure clamps are torqued firmly; you should not be able to rotate the clamp with hand pressure alone. Inspect hose condition near the fittings for cracking, surface hardening, or swelling, which indicate the hose material is deteriorating. Below-waterline hose failures are infrequent but are high-consequence events when they occur.

ContextGrasp the rudder blade with both hands and check movement in three axes: side-to-side (athwartships) play in the bearing arrangement, up-and-down (vertical) movement indicating worn pintles or gudgeons, and twisting or racking movement in the blade itself. A small amount of rotational play — 1–2mm — is normal in most bearing arrangements. Athwartships play exceeding 5mm, or any vertical movement, needs investigation. Loose rudder bearings wear exponentially under sailing loads; 5mm of clearance becomes 15mm or more within a single season of active use. Also check that all gudgeon fastenings are present, fully tightened, and show no corrosion at the hull or transom interface.

ContextTap the rudder blade surface in a grid pattern with a knuckle or small hammer. Hollow sounds in what should be a solid blade, or irregular variation in tone across a laminated blade, indicate internal delamination or voids. Probe any crazing or cracking in the protective finish, particularly at the leading and trailing edges where surface checking begins first. Waterlogging is confirmed by weight gain: weigh the rudder before launch each season. Weight gain exceeding 5–10% in a solid wooden rudder confirms ongoing water absorption. A severely waterlogged rudder overloads the stock and bearings and may conceal internal rot that is invisible from outside.

ContextPintles and gudgeons should be bedded firmly in polysulfide or similar compound with no visible gap at the hull interface. Rock each fitting individually — any movement in the fitting itself, as distinct from the rudder bearing play you checked separately, indicates fastening failure or soft backing wood beneath the fitting. Inspect bronze fittings for dezincification: a pale pink coloration instead of warm gold, or a chalky surface, indicates zinc is leaching from the alloy. A dezincified fitting retains its shape but breaks at a fraction of its rated load. This occurs most often in lower-quality castings and in low-oxygen environments, and is a reason to replace rather than monitor.

ContextThe stem is the forward vertical timber into which the forward plank ends land. The rabbet cut into the stem to receive these plank ends is a continuous moisture trap: water running down the planking collects at every plank end. The apron — the backing timber inside the stem — often develops serious rot before the stem face, because it stays wet and has limited ventilation. Press the ice pick firmly at every plank hood end along the stem face and rabbet line. Soft spots here are expensive to address correctly — stem replacement in a typical wooden cruiser runs $1,500–$5,000 depending on access and size — but they are structural. A rotten stem allows plank ends to pull free under sailing loads.

ContextTransoms are frequently underdone in surveys because they are less visually dramatic than bottom planking, but every horizontal joint in the transom collects water, and ventilation behind the transom is typically poor. Sound the transom planking both vertically and horizontally; dull spots away from fastenings indicate internal softness. The transom knee — the structural curved timber connecting the transom to the keel — is critical: it is usually a single large piece of grown or curved timber, and rot here compromises the integrity of the entire stern structure. Access it through the lazarette or aft bilge and probe the forward face directly.

ContextThe turn of the bilge — where topsides planking curves into the bottom planking — experiences the greatest cyclical flexing of any seam on the hull. Caulking here is subjected to both the paint build-up cycles of haul-out seasons and the immersion cycles of the sailing season, making it the first place to show compound failure. Run a pick along this transition seam from stem to transom on both sides, checking for gaps, compound that has fully fallen away, or areas where compound is present but has separated from one plank edge. Any discontinuity in this seam needs remediation before launch.

ContextChoose one inconspicuous location on each side — typically mid-hull at the turn of the bilge — and scrape down through all anti-fouling layers to bare wood or primer with a stiff putty knife. Count and photograph the cross-section. More than 8–10 layers of anti-fouling creates a surface that no longer bonds predictably, adds meaningful weight to the underwater hull, and can conceal surface conditions beneath. Plan for a full chemical strip or careful disc-sand every 5–8 years; this costs $800–$2,500 professionally or significant time if done yourself. Note whether any layers appear to be an older formulation — copper loading regulations vary by region and are being progressively tightened.

ContextOsmotic blistering on wooden hulls is less common than on fiberglass but occurs on cold-molded or strip-planked boats with epoxy sheathings, and on hulls with oil-based primers trapping moisture beneath a less permeable topcoat. If you find blisters, open one with the pick: fluid that smells acidic, is yellowish, or contains visible sediment indicates active osmosis beneath the coating. Clear, odorless fluid suggests mechanical delamination rather than chemical osmosis. Record blister size (use pea, marble, or golf ball as reference categories), density per square foot, and distribution — blistering concentrated at the waterline transition has different causes than blistering spread uniformly across the running bottom.

ContextTap the bottom surface firmly with a knuckle in a systematic grid, roughly 12 inches apart. A hollow response — like tapping an empty box versus a solid table — indicates paint layer separation from the substrate beneath. This is distinct from osmotic blistering and typically results from inadequate surface preparation, incompatible paint system layering, or application over a silicone-contaminated surface. Delaminated areas peel in sheets during pressure-washing and will continue to fail progressively. Estimate the percentage of hull bottom surface showing hollow response; if delamination covers more than 20% of the surface area, a full strip and reprimer coat is more economical than patching the perimeter of each delaminated zone.

ContextThe haul-out period is your best opportunity to inspect frames from the bilge side — the boat is accessible, bilge water is minimal or absent, and any seasonal weeping from above-water seams is not obscuring the picture. Probe every accessible frame at and below the waterline level, particularly where frames pass through floor timbers or land on the keel. Softwood frames such as spruce or Douglas fir are more vulnerable to rot than hardwood frames, but any species will fail if the frame-to-planking interface remains persistently wet. A frame that allows the pick to enter with hand pressure needs either sistering — adding a new laminated frame alongside — or replacement. Document every suspect frame by frame number or position.

ContextWater that enters through an exterior seam or fastening travels along the interior plank surface and drips onto the frame below, producing a characteristic stain at the frame top or floor timber. Fresh staining — bright orange-rust or clean brown — means the leak is recent or ongoing. Old staining — dark, dry, no associated softness — may reflect a repair completed years ago with no current activity. Cross-reference every interior stain against your exterior sounding and probing map. Where exterior soundings are clean and there is no interior staining, the area is clear. Where you have exterior softness without interior staining, moisture has not yet propagated inward — an early-stage finding worth treating promptly.

ContextA clean, dry-smelling bilge after an adequate period on the hard is your target. A persistent musty or earthy smell in a dry bilge indicates active fungal decay somewhere in the structure — the odor of wood rot is distinctive and does not come from clean, inert timber. Use a moisture meter to record readings at five fixed reference points: bow section, forward sections, amidships, aft sections, and stern. Photograph the dry bilge for your records. These readings define your specific boat's 'normal dry' baseline — a reading significantly elevated next season indicates water ingress you have not otherwise traced. An undated, unmeasured bilge tells you nothing; a measured, photographed bilge tells you exactly what changed.

ContextA simple profile view and plan (top-down) view with numbered findings cross-referenced to your notes is far more useful than written descriptions alone. Use category codes: R for rot, S for soft or suspect, FC for fastening corrosion, SC for seam or caulking failure, TH for through-hull concern, RD for rudder system, and ST for stem or structural timber. Rate severity: 1 means safety-critical and do not launch, 2 means pre-launch repair required, 3 means complete before next haul, and 4 means monitor annually. This coded map becomes a searchable record — after five annual surveys you can identify which areas of your hull are persistently flagged and which are genuinely stable.

ContextSeverity 1 — safety-critical — means the boat could take on dangerous water during normal use. This includes: a weeping garboard seam that does not close under probe pressure, a seized seacock that cannot be operated, a stem with through-rot at multiple plank hood ends, or a keel joint showing active weeping. Severity 1 items do not launch until resolved. Severity 2 — pre-launch required — means the condition will worsen significantly if the boat is immersed without repair: moderate rot in a single plank, open seams wider than 3mm, corroded through-hull backing blocks. Severity 4 — monitor — means the finding is documented, stable, and will be re-examined. The mental hazard is the escalation from 4 to 1: a finding that seems manageable is often the beginning of a much larger problem. Be honest about severity classifications; you are the one sailing the boat.

ContextWooden boat repair costs vary substantially by region, yard, and craftsperson. Get written estimates — not verbal commitments — that specify materials, method, and scope in enough detail that a different contractor could price the same job. A skilled boatwright who charges $95 per hour and completes the work correctly once is nearly always less expensive over five years than a general marine yard at $65 per hour that patches and re-patches. Ask each estimator explicitly whether the scope covers the described work only, or includes any adjacent repairs that may become necessary once the job is opened up. Scope expansion on wooden boat work is normal and legitimate; wood problems rarely have clean edges.

ContextEvery 'monitor' finding needs a defined future check date written into your calendar, not just into the survey log. Mid-season — 60–90 days after launch — is appropriate for findings you are actively watching for change. Next annual haul-out is appropriate for genuinely stable, well-documented findings that have shown no change across at least two consecutive surveys. An undated monitor item is an item that will be forgotten. Update the severity code next year and note whether the finding has changed, improved, or worsened. Three consecutive annual surveys showing no measurable change is reasonable evidence of genuine stability. Two surveys showing clear worsening upgrades the finding to Severity 2 at minimum, regardless of how inconvenient the timing is.