Let me tell you a story that might sound familiar.
A buyer in the Netherlands has spent all spring looking for a 9 m boat. Then he finds it: the right layout, sensible engine hours, a fair price, and a gyro stabiliser already fitted. He assumed that would cost him a premium.
Then the pre-purchase survey comes back. The surveyor found a bonded plinth under the aft berth with gelcoat crazing at two corners. There was no mention of the installation anywhere in the boat’s file. The builder’s Declaration of Conformity described a boat weighing rather less than the one floating in front of him.
The gyro runs. It is probably fine. But nobody can prove it.
The sale completed three weeks late, at 8% under the asking price, and the seller paid for a structural inspection he hadn’t budgeted for. The gyro, which should have been an asset, cost him roughly the price of the gyro.
I’m sharing this because it happens more often than it should, and it is entirely preventable.
The problem isn’t the modification. It’s the gap in the file.
The European second-hand market for small craft has become much more document-driven over the past decade. Buyers are better informed, surveyors are more thorough, and insurers and lenders ask harder questions. Cross-border sales bring VAT status, RCD conformity and registration into every conversation.
In that environment, an undocumented structural or electrical modification is a red flag, however well it was done. The buyer isn’t worried that a gyro is a bad idea. He’s worried about three things he can’t see:
• What exactly was changed, and whether the hull structure was engineered for it
• Who did the work, and whether they’re still in business if something fails
• Whether the boat still matches its certification and insurance basis
When those worries are unresolved, they get priced as a discount. When they’re documented, the discount disappears. It’s unusually simple arithmetic for a market that usually isn’t.
For sellers: the twelve documents to have ready
If you’re selling a gyro-equipped boat, gather these before you list. Brokers, ask for them before taking the listing. Buyers, ask for them before paying for a survey.
1. Original CE Declaration of Conformity and owner’s manual, with the builder’s technical file reference if available
2. Gyro model, serial number and purchase invoice
3. Installation drawings and structural reinforcement scheme: foundation design, scantlings, laminate schedule or weld detail, and design loads. This is the document that turns “someone glued a box in” into “an engineer specified this.”
4. Weight, VCG, LCG and GM calculation. It doesn’t need to be a full stability book on a 4-tonne boat, but it does need to exist.
5. Installation photographs, dated, showing the foundation before closing up, the bolt pattern and backing plates, tabbing, isolators, and pipe and cable runs
6. Electrical schematic and battery capacity calculation, as installed
7. Cooling circuit schematic (or airflow and ventilation documentation for air-cooled units)
8. Sea-trial and commissioning report, gyro off and on, with measured data rather than adjectives
9. Maintenance records: bearings, isolators, cooling flushes, firmware updates
10. Warranty transfer documentation. Know what applies before a buyer asks.
11. Insurance endorsement or notification record, which shows the modification was treated as legitimate from day one
12. Installer’s declaration: company, contact, competence or approval status, standards worked to, signature and date
My practical tip is to bind it all as one PDF with a contents page. A surveyor who receives it in advance spends his time looking at the boat instead of reconstructing its history, and you get a better report for the same fee. It’s roughly a day’s work, and usually worth several times the price adjustment you’d otherwise absorb.
For surveyors (and buyers curious about what good looks like)
Seven checks, none of them exotic:
• Foundation and structure: gelcoat crazing radiating from plinth corners (the classic early sign of cyclic load exceeding the local laminate’s fatigue capacity), disbonding at the tabbing toe, and weld toes on metal hulls
• Fasteners: corrosion, elongated holes, missing backing plates, dissimilar metals
• Isolators: set, cracking, oil contamination, and uneven compression across the mount set
• Cooling circuit: hose specification, double clips, strainer, seacocks, and any salt tracking that suggests a slow weep
• Electrical: discoloured terminals, cable and protection ratings, and whether the gyro can be isolated without killing the whole house supply
• Software and controller: firmware version and fault log. Many controllers record more than owners realise.
• Run it: listen, feel the bulkheads, check spin-up time against the manufacturer’s figure
For brokers: how to write the listing
There’s a temptation to resist here. Please don’t write “95% roll reduction.” It means nothing without sea state, heading, speed and loading. Knowledgeable buyers know that, and it invites exactly the scepticism you wanted to avoid. It can also come back as a misrepresentation argument.
Try this instead: “Gyro stabiliser fitted 2023, professional installation, full documentation pack available, sea-trial report on file.”
That sentence tells a serious buyer the boat will survive a survey. Two more tips:
• Say whether it’s a factory option or a retrofit. They carry different risk, because a factory fit sits inside the builder’s original design and certification work.
• Publish the pack summary, not the pack. A one-page contents list in the listing signals rigour, and the full file follows after a viewing.
For buyers: what to negotiate
• No documentation? Ask for a discount that reflects the risk, a structural inspection at the seller’s cost, or a retention held against findings.
• Full documentation? Expect to pay for the comfort. A well-documented, professionally installed system is genuinely valuable. Argue about the number, not about whether there is one.
• Sea trial, gyro off and on. Same conditions, same heading, same loading, back to back, fifteen minutes each. If the seller refuses, it’s fair to ask why.
• Check warranty transferability before completion. It’s a five-minute email that occasionally changes the price.
• Get your insurer’s position in writing before you complete. It costs nothing and closes off the worst surprise in the process.
Over to you
I’d love to hear from the brokers, surveyors and yards reading this. On the gyro-equipped boats you’ve sold or surveyed, which single document moved the deal most, and which missing one cost the seller the most?
We’d like to build the next version of this checklist from real transactions rather than from theory, so please share your experience in the comments.