Pre-purchase GRP and steel hull surveys, out of the water

Before the lift

We ask the yard to haul early in the day, so the hull has as many dry hours as possible before we read it. While the boat is still in the water we note her trim against the builder’s marks, check the bilges for standing water and look at the boot top for weed lines that sit higher than they should. A boat that floats low aft is often carrying water in a cored deck or a sodden stern locker.

Once she is up, the first look is with the pressure washer still running. Blisters weep, cracks show up as lines of fine bubbles, and old repairs often show as a patch that dries at a different speed from the rest of the bottom.

Sovellus capacitance moisture metering

A capacitance meter sends a small field into the laminate and reports how much it is disturbed. Water disturbs it a lot. So do metal, carbon fibre, lead ballast and some antifouling paints. That is why a meter reading is a pointer, not a verdict.

We chalk a grid on the bottom, roughly one cell per 40 cm, and read every cell on the Sovellus relative scale. We then read the topsides above the waterline as our own dry reference for that hull. A bottom that reads close to its own topsides is dry, whatever the absolute number says.

• Readings are repeated after 24 and 72 hours on any hull that came out wet. A falling number is surface water. A number that holds is in the laminate.
• High cells are scraped back to gelcoat and read again, so paint is ruled out.
• Over the keel, the engine beds and bonded tanks, readings are noted but not trusted. We use the hammer and our eyes there instead.

Phenolic hammer percussion testing

Most production yachts since the 1980s have cored decks and many have cored topsides. Balsa and foam cores are light and stiff until water gets in at a deck fitting or a stanchion base. Then balsa rots and foam loses its bond, and the outer skin starts working on its own.

We sound cored areas with a light phenolic hammer, cell by cell. A sound laminate rings sharp. A delaminated patch sounds dull or dead. We map dull patches on the deck plan, then check each one with the meter and, where it matters, a small test hole drilled from inside and filled before we leave.

Ultrasonic thickness on steel and aluminium

On a metal hull the hammer gives way to the ultrasonic gauge. We use multi-echo mode, which measures the steel between two back-wall echoes and ignores the paint, so we do not have to grind the coating off to get a true reading. Each station is fixed on the lines plan and recorded in the sounding schedule, nominal against measured, so the next surveyor can go back to the same spot.

The places that thin first are nearly always the same: the engine room bilge under trays and pumps, around sea chests, at the boot top where the water line wets and dries, and in the shadow of anodes that have been allowed to waste away. On aluminium we look hard at any place where a stainless fitting, a copper-based paint or a shore power fault could have set up galvanic corrosion.

Keel bolts and crevice corrosion

Stainless steel is stainless because oxygen keeps a thin passive film on its surface. Deep inside a keel stub, wet and starved of air, that film can break down. The bolt then corrodes in the crevice where nobody can see it, often looking perfect at the nut.

We look at the keel-to-hull joint for a weeping seam or a smile, the line that opens at the leading edge when the keel has been knocked. Inside, we check the floors and the matrix around each bolt for cracks and rust stains. On older boats with stainless bolts and any history of grounding, we recommend drawing one bolt for inspection. It costs a day of yard time. It is the only way to know.

• Mild steel bolts in iron keels: expect surface rust, look for necking at the joint.
• Stainless bolts in lead keels: the crevice risk is highest, and the bolt looks fine until it is drawn.
• Encapsulated keels: check the bilge sump for water that should not be there.

Rudder stock clearances

With the boat ashore we put a shoulder to the rudder blade and push it fore and aft, then side to side. Any knock is measured with feeler gauges at the lower bearing and checked again from inside at the upper bearing. We compare the clearance with what the builder or bearing maker allows. A worn bearing is cheap. A worn stock is not.

On GRP rudders we also meter the blade. Water that gets in around the stock freezes in a northern winter and splits the blade, and even in the Adriatic it corrodes the internal web where the stock is welded. A rudder that reads wet at the top and dry at the bottom is a rudder worth dropping.

What you get

The dossier lists every finding in one of three groups: safety items to fix before the boat goes to sea, items that affect value and should go into the negotiation, and items for the owner’s list. Each has a photograph, a position on the lines plan and, where we can, a rough yard price from the Upper Adriatic. Banks and underwriters accept the report as a condition and valuation survey.