Boat Survey Checklist: What to Check Before Buying

A professional marine survey is the single most important step in buying a used boat. A surveyor identifies problems that are invisible to the untrained eye and can save you thousands — or prevent a bad purchase entirely. This checklist covers what a surveyor checks and what you should look for during a pre-survey viewing.

Why you need a survey

Even an experienced boater benefits from a survey. A surveyor works with moisture meters, thermal imaging, and hull tap testing — tools and techniques that reveal problems no visual inspection can detect. Most insurers require a survey for boats over 10 years old, and most lenders require one for financed purchases. A survey costs €400 to €800 for a typical 30 to 40-foot boat — a small fraction of the purchase price.

Hull and deck

The hull is the most critical structure. A surveyor checks for:

• Osmosis blistering: Small blisters in the gelcoat indicate water penetration into the laminate. Minor blistering is common on older boats; extensive blistering requires expensive treatment (€3,000–€8,000).
• Core delamination: Balsa or foam-cored decks and hulls can delaminate if water enters through fastener holes. The surveyor taps the hull with a plastic hammer — dull spots indicate delamination.
• Hull-deck joint: Separation or cracking along the join line suggests structural stress or a poor factory joint.
• Keel attachment: On fin-keel boats, the surveyor checks the keel-hull joint for movement, cracks, or weeping. Keel bolt condition is assessed during haul-out.
• Through-hull fittings: Every underwater fitting is checked for corrosion and proper operation. Bronze seacocks should be reddish — pink indicates dezincification and imminent failure.

Engine and propulsion

• Engine hours: Verified against the hour meter. Under 2,000 hours is mid-life for a marine diesel; over 5,000 suggests a rebuild or replacement is due.
• Oil and coolant: Milky oil indicates water intrusion — a serious problem. Coolant should be clean and at the correct level.
• Belts and hoses: Cracked or perished belts and hoses indicate deferred maintenance.
• Engine mounts: Cracked or corroded mounts allow vibration and misalignment.
• Exhaust risers: Corroded risers allow water back into the engine. Replacement costs €1,500–€3,000 per engine.
• Saildrive or stern drive: Checked for oil leaks, rubber diaphragm condition, and bearing wear.

For a detailed engine comparison, see our guide on outboard vs inboard engines.

Rigging and sails (sailboats)

• Standing rigging age: Rigging over 10 to 15 years old is assumed to need replacement. The surveyor checks swage fittings for rust, cracked strands, and bent turnbuckles.
• Mast and boom: Checked for corrosion, dents, and spreader root cracks.
• Sails: Inspected for UV damage, torn stitching, and worn bolt ropes. A new mainsail and genoa for a 30-footer costs €3,000–€6,000.
• Winches: Checked for smooth operation and corrosion.

Electrical and plumbing

• Wiring: Marine-grade tinned wire is required. Untinned domestic wire corrodes and is a fire risk. The surveyor checks for proper fusing, wire chafe, and corrosion at terminals.
• Batteries: Age, type, and condition. House banks over 5 years old may need replacement.
• Bilge pumps: Tested for flow rate and automatic switch operation.
• Water system: Checked for leaks, tank condition, and pump operation.
• Marine toilet: Checked for proper operation and holding tank condition.

What to check during a pre-survey viewing

Before you pay for a survey, do your own initial viewing to decide whether the boat is worth the surveyor's fee. Check for:

• Persistent damp or musty smell below decks
• Water stains on the headliner (traces leaks to their source)
• Soft spots on the deck (press with your knee)
• Cracked or faded gelcoat (indicates age and UV exposure)
• Engine oil colour and level (milky oil = walk away)
• General cleanliness and maintenance signs (a clean boat is usually a cared-for boat)

For a more detailed walkthrough, see our marine surveyor guide and our complete used boat buying guide.

Sea trial

A survey includes a sea trial — a test run under power and (for sailboats) under sail. The surveyor checks:

• Engine temperature and oil pressure under load
• Steering response and play
• Sail handling and rig behaviour under load
• Speed through the water vs GPS speed (indicates hull fouling)
• Vibration or unusual noises

Never waive the sea trial. Problems that are invisible at the dock reveal themselves underway. Once the survey and sea trial are complete, you can negotiate repairs or price adjustments based on the findings. Browse boats for sale on Owning.pro to find your next boat.