By Jean Levine, Retired SAMS Accredited Marine Surveyor & Jeff Grossman, BSEE
Marine surveys are essential when buying a boat, but even the most thorough and professional survey has its limits. Despite industry certifications, rigorous standards, and decades of experience, there are many issues that simply cannot be discovered during a single day at the dock and a brief sea trial.
After nearly 50 years in the marine world – and hundreds of surveys followed by onboard training voyages – we’ve seen firsthand how problems can reveal themselves only after the sail. This article outlines what marine surveys can and cannot uncover, with examples from real-life scenarios on sailboats ranging from 30 to 65 feet.
The Role of the Surveyor
Today’s professional surveyors are certified by either SAMS (Society of Accredited Marine Surveyors) or NAMS (National Association of Marine Surveyors). Both organizations require deep industry experience, education, exams, and a multi-year apprenticeship before designation as an AMS (Accredited Marine Surveyor) or CMS (Certified Marine Surveyor).
Still, even the “Best Surveyor in the World” cannot inspect what they cannot see, or test systems that aren’t in use, during the survey. A marine survey is, above all, a snapshot in time – an assessment of the vessel’s condition on that particular day.
Common Issues That Hide from Surveys
1. Fuel Gauges
Fuel gauges are rarely accurate and seldom tested under real use. Tanks may show a reading but fail to respond during extended motoring. Surveyors can power up the gauge but not verify actual fuel levels or sensor function without access ports or extended run time.
Tip: Always keep diesel pads handy the first time you fuel up.
2. Holding Tanks & Macerators
Most sellers empty and flush holding tanks before a survey. Surveyors can test whether pumps power on but cannot confirm full-system function or performance under load.
Example: A 46’ sailboat passed a survey with working macerators. On its first voyage, the pumps failed once the tanks filled.
3. Leaking Tanks
Leaks – especially those on the tops or hidden sides of tanks – often don’t show up unless the tanks are full, the boat is underway, or a temporary patch fails.
Best Practice: Be ready to monitor and replace aging stainless tanks, especially on budget-built vessels.
4. Outboard Motors
Outboards may start at the dock but fail under load or prolonged use. Surveyors typically can’t run them long or under realistic conditions.
Powerboat Buyers: Always get a certified engine mechanic to inspect larger outboards.
5. Corrosion
Surveyors can spot visible corrosion but can’t remove every clamp, inspect behind cabinetry, or test every joint. Hidden corrosion often shows itself during the first use at sea.
Real Case: A corroded hose clamp passed visual inspection and then failed at sea, causing bilge water intrusion.
6. Moisture Detection
Moisture meters are unreliable in rain or high humidity. Tapping with a phenolic hammer helps, but minute voids may go undetected.
Pro Tip: Ironically, rain during a survey can help reveal active leaks.
7. Canvas & Soft Goods
Bimini and dodger canvas might look fine, but their waterproofing may have deteriorated. Surveys can’t confirm water resistance unless it’s actively raining.
8. Rigging: The Hidden Parts
Tape-wrapped sections, spreader boots, and below-deck chain plates are often inaccessible. Surveyors inspect what’s visible, but critical failures may lurk out of sight.
9. Electronic Systems
- SSB & VHF: Surveyors may confirm power-up but cannot guarantee range or transmission without on-water testing.
- AIS: This needs to be tested in open water or a busy harbor for range verification.
- Cell Boosters: These only work within a narrow band of signal strength and are tough to test in port.
10. Wiring Complexity
Surveyors check labeled switches and test functionality, but tracing unlabeled wires or evaluating custom installations (like complex charging systems) is beyond the scope of a one-day visit.
11. Outlets
A survey isn’t a full house inspection. On boats with dozens of outlets, surveyors test a sampling, not every socket – especially low-load 12V ports, which may have voltage but fail under actual load.
12. Battery Health
Most boats are connected to shorepower during the survey. A weak battery may appear fully charged. Brief voltage drop tests can help, but only prolonged anchoring and cycling will reveal the true condition.
13. Sea Trials Are Short
Surveys rarely include heavy-weather sailing. Some faults only emerge when the vessel is heeled, pitching, and under load.
Example: A taped speaker wire passed dock inspection, but failed after sailing in swell.
14. Load Failures
High-load systems like anchor windlasses and fuel transfer pumps may power on during the survey but fail under stress.
15. In-Mast Furling Systems
These systems often fail under load when reefed – something a calm sea trial can’t replicate. Internal pawl issues are particularly elusive.
16. Engine & Oil Systems
Oil analysis is only useful if the seller knows the number of hours since the last oil change. Otherwise, the data is meaningless or misleading.
Fuel System Tip: Always polish and clean fuel tanks before a delivery voyage – sludge may sit harmlessly until stirred up at sea.
Final Thoughts
A Marine Surveyor is like a General Practitioner: knowledgeable across systems, trained to spot trouble, and experienced in knowing when to recommend a specialist. Their job is to document the vessel’s condition, not offer guarantees.
No matter how skilled your surveyor is, some issues will only emerge after you start using your boat – especially offshore. The examples above are not faults of the survey process but reminders of its limitations.
Next time you encounter a post-purchase surprise, stop and ask: “Could this reasonably have been found on survey day?”
Standard Disclaimer from Marine Surveys
“No reference or information should be construed to indicate evaluation of the internal condition of the engine or the propulsion system’s operating capacity…. Electronic equipment was checked for ‘power up’ only…. This vessel was surveyed without removals of any parts, including fittings…. This survey report represents the condition of the vessel on the above dates, and is the unbiased opinion of the undersigned, but it is not to be considered an inventory or a warranty either specified or implied.”
Join The Discussion
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What surprised you most after buying your boat and could a survey have caught it
Marine surveys are incredibly valuable, but as this article explains, they are not crystal balls. Let’s talk about real experiences. What issues did you encounter after your purchase? In hindsight, do you think they were avoidable? And how do you now approach pre-purchase inspections or sea trials differently?
https://americansailing.com/articles/things-a-marine-survey-cant-tell-you/
americansailing.com
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