At a Glance
| What a survey is | A condition report from a qualified professional — not a pass/fail inspection |
| Cost | Typically $20–$25 per foot of boat length, paid by the buyer |
| Accreditation | SAMS (Society of Accredited Marine Surveyors) or NAMS (National Association of Marine Surveyors) |
| Who pays | The buyer — always. Never use a surveyor recommended by the seller or broker |
| What it doesn't cover | Engine, sails, electronics — these require separate specialists |
| Sea trial | Should always accompany the survey; some surveyors require it, others treat it separately |
A marine survey is one of the most important steps in buying a used sailboat, and also one of the most misunderstood. Buyers often approach the survey as if it will tell them whether to buy the boat. It won't. What it will tell you is the condition of the boat on the day it was surveyed — and condition reports rarely say "walk away" in those terms. They list deficiencies. Your job is to decide what those deficiencies mean for the price and whether you want to own them.
Understanding what a surveyor does, what they don't do, and how to use the results gives you real negotiating leverage. Walking into the process without that understanding means you're paying $700 to $1,500 for a document you don't know how to use.
The Two Accreditation Systems
In North America, the two recognized credentialing bodies for marine surveyors are SAMS (the Society of Accredited Marine Surveyors) and NAMS (the National Association of Marine Surveyors). Both require training, examinations, and ongoing continuing education. Neither credential is legally required to practice as a marine surveyor — anyone can legally call themselves one — which is exactly why the credential matters.
SAMS designations: AMS (Accredited Marine Surveyor) is the standard credential; SAMS-Master is the senior designation. NAMS designations: CMS (Certified Marine Surveyor) is the professional standard. Both organizations maintain directories of credentialed members searchable by location and specialty. When you find a surveyor you're considering, verify their credential directly on the organization's website. Lapsed, revoked, or fabricated credentials exist in this industry.
Surveyors also specialize. A surveyor who primarily does fiberglass production boats may not have the depth of experience needed for a classic wooden schooner or a metal-hulled offshore passage maker. Check that your surveyor's experience matches the boat type you're buying.
The Most Important Rule: Find Your Own Surveyor
Never use a surveyor recommended by the seller. Never use a surveyor recommended by the broker. A surveyor who wants repeat business from a broker will not produce reports that kill deals. They may not produce false reports — but they may describe significant problems with language that undersells their severity, may fail to follow up aggressively on marginal findings, and may have a professional incentive to see the transaction close rather than to protect your interests.
The surveyor you hire works for you. If you find one through a broker referral, assume a conflict of interest until proven otherwise. Find your own through the SAMS or NAMS directories, through recommendations from sailors you trust (not the people selling you the boat), or through sailing club networks. Get references and call them.
What a Survey Covers
Hull Integrity
The hull inspection is the centerpiece of the survey and requires the boat to be hauled out of the water. The surveyor examines the exterior hull for impact damage, stress cracking, signs of repair, and osmotic blistering. They will use a moisture meter across the hull surface to detect elevated moisture content in the fiberglass laminate — a precursor to serious blistering, and invisible from the surface. High moisture readings in isolated areas may be acceptable; high readings across a wide swath of the hull suggests ongoing water intrusion into the laminate.
Osmotic Blistering
Osmosis in fiberglass hulls occurs when water passes through the gelcoat and reacts with water-soluble compounds in the laminate, creating acidic fluid that forms bubbles. Mild blistering — small, isolated blisters in the gelcoat — is common in boats over 20 years old and is a cosmetic concern more than a structural one. Severe blistering that has penetrated into the structural laminate is expensive to repair, requiring hull drying, blister grinding, and a full barrier coat application. The surveyor's report will characterize severity. If severe blistering is present, get a remediation estimate before proceeding.
Chainplates
Chainplates are the fittings that attach the standing rigging — the shrouds and backstay — to the hull structure. They are one of the highest-load fittings on the boat, and they are often concealed behind interior liners where water can collect and cause corrosion that is invisible until failure. Chainplate failure causes mast loss. A competent surveyor will inspect chainplates where accessible and note any that require removal for proper inspection. If a seller is unwilling to allow chainplate inspection, that is a problem.
Keel Attachment
On fin-keel boats, the keel is attached to the hull with keel bolts — typically bronze or stainless steel studs running through the hull into the keel. Keel bolt corrosion is a serious structural issue; keel separation from the hull is catastrophic. The surveyor will inspect the bilge area around the keel sump for rust staining (indicating corroding keel bolts), movement at the hull-keel joint, and any signs of water intrusion at the joint. Boats with corroded keel bolts are not unsalvageable, but the remediation is expensive and the boat should not go offshore until it is done.
Through-Hulls
Every hole in the hull below the waterline — for the head, engine cooling, cockpit drains, depth transducer — is a through-hull, and each one is a potential failure point. The surveyor will inspect each through-hull fitting and its associated seacock for corrosion, proper operation, and evidence of leaks. Seacocks that won't close are non-functional safety equipment. Through-hulls made of plastic (ABS) rather than bronze or Marelon are a concern on any boat that will go offshore.
Rig Inspection
The surveyor will inspect the standing rigging for corrosion, kinking, broken strands, and the condition of swaged terminals and toggles. They will check the mast base for corrosion and the chainplates as noted above. A full rig inspection sometimes requires going aloft, though not all surveyors do this as standard practice — ask explicitly whether going aloft is included, and if not, consider hiring a rigger separately for a rig inspection.
What Surveyors Don't Cover
A standard marine survey is not a comprehensive mechanical or systems inspection. The three areas that fall outside most surveys:
The engine. A marine surveyor will typically run the engine and note obvious problems, but they are not diesel mechanics. If the engine has significant hours, a questionable maintenance history, or any symptoms during the sea trial, hire a diesel mechanic separately to do a compression test and mechanical assessment.
Sails. Surveyors rarely inspect sails beyond a visual check. If the sails are critical to your purchase decision — the boat is being represented as ready to sail offshore — have a sailmaker inspect them, or at minimum ask for the sails to be set so you can see their condition.
Electronics. Navigation instruments, chartplotters, VHF radios, autopilots, and radar are typically noted as present but not tested or assessed in detail. Assume they may need replacement and budget accordingly.
The Sea Trial
The survey should always include or be accompanied by a sea trial — the boat under power and under sail, with the surveyor aboard. The sea trial reveals things the dock inspection cannot: how the engine performs under load, how the boat handles in a seaway, whether hatches leak when the boat is heeled, whether there are alarming sounds from the rig under sail loads, and whether the autopilot tracks properly. Do not let anyone talk you out of a sea trial. A seller who won't allow one has something to hide.
Negotiating Off Survey Findings
The survey report is a negotiating document. Findings that require immediate correction — failed through-hulls, corroded keel bolts, standing rigging past its service life — are legitimate bases for price reduction. Get repair estimates from qualified yards before negotiating. Come to the seller with dollar amounts, not percentages.
Not every finding warrants a price reduction. Minor deficiencies, cosmetic issues, and items that are expected on a boat of that age don't justify a second round of negotiation. Pick the three or four most expensive and legitimate items and present them clearly. Sellers respond poorly to buyers who try to renegotiate every line item in the report.
When to Walk Away
Walk away if: the keel bolts are severely corroded and the seller won't reduce price to cover remediation. Walk away if: the hull moisture readings indicate the laminate is saturated and the boat needs a full blister job the seller won't acknowledge. Walk away if: the chainplates cannot be inspected because of the interior configuration. Walk away if: the seller refuses a sea trial. Walk away if: you've fallen so in love with the boat that you find yourself rationalizing findings that would clearly disqualify any other boat. That last one is the hardest and the most important.
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Frequently Asked Questions
What does a marine survey typically cost and who should perform it? A professional marine survey costs approximately $20 to $25 per foot of overall boat length, so a 40-foot sailboat survey runs $800 to $1,000. The surveyor should hold credentials from the Society of Accredited Marine Surveyors (SAMS) or the National Association of Marine Surveyors (NAMS), both of which require training, experience, and ongoing professional development as conditions of membership.
What is osmotic blistering and why does it appear in survey reports? Osmotic blistering is a condition in fibreglass hulls where water penetrates the gelcoat and reacts with the laminate, forming blisters ranging from pinhead-sized to golf ball-sized below the waterline. It is caused by water migrating through the gelcoat into the laminate where chemical compounds attract further water by osmotic pressure. Minor blistering is a cosmetic maintenance issue; widespread blistering deep into the laminate requires professional barrier coat treatment and is a significant survey finding.
Why are chainplates a critical item in a sailboat survey? Chainplates are the fittings that attach the standing rigging to the hull, and they are among the highest-stress structural connections on the boat. Crevice corrosion in stainless steel chainplates occurs in the oxygen-depleted environment of a sealed deck fitting and can reduce the chainplate's strength to a fraction of its rated capacity without any visible surface sign. Surveyors look for evidence of deck leaks at chainplate penetrations, corrosion staining, and any visible cracking of the surrounding deck structure.
What does a surveyor check about keel bolts? Keel bolt inspection involves checking the accessible nuts inside the boat for signs of rust or movement, probing the bedding compound at the keel-hull joint from outside, and using a moisture meter in the laminate around the keel attachment area. Corroded, loose, or missing keel bolts are a serious structural deficiency; a keel that separates at sea is a catastrophic event. Professional keel bolt inspection with torque testing is recommended for any boat over ten years old.
What are through-hull fittings and why do surveyors inspect them carefully? Through-hull fittings are the valves and skin fittings that penetrate the hull below the waterline for engine cooling, sink drains, cockpit drains, and other systems. Each through-hull is a potential water entry point if the seacock fails or the fitting corrodes. Surveyors check that each through-hull has a functional seacock that can be closed, that the fitting material is appropriate for the installation, and that there is no dezincification or corrosion that would indicate impending failure.