Most boats sold are used boats
Pre-owned transactions are roughly 78 to 80% of all US boat sales. The typical buyer is not evaluating a warranty and a build sheet; they are evaluating someone else's maintenance decisions over five or ten years, described by the person who made them.
Palm Beach County raises the stakes. There are 37,905 registered vessels in the county, 28,904 of them in the 12 to 40 foot outboard band, and boats here run twelve months a year in salt water with no layup to interrupt wear. Hours accumulate faster and corrosion never pauses. The most useful thing a buyer can do before wiring money is put instruments on the engines, because on an outboard boat they are most of what can go catastrophically wrong after closing.
Stated hours and ECU hours often disagree
The number on the dash is a display. The number in the engine control unit is a record. They come apart for ordinary reasons and dishonest ones, and the inspection reports the gap rather than guessing at the motive.
Ordinary reasons: a gauge replaced during a rigging update started from zero, an hour meter counts key-on rather than run time, a seller quoted an old listing, or a hull with twins had one powerhead replaced. The other reason is misrepresentation. Depending on brand and model year, many outboard ECUs store more than a total: hours logged within each RPM band, plus recorded over-rev, overheat and low-oil events. That separates 600 easy hours at cruise from 600 spent pinned at wide-open throttle, and it is the part buyers most often say changed their offer. Hours, codes and event history are read with the manufacturer's diagnostic interface and photographed into the written record.
Compression, and what a low cylinder actually means
Compression is measured with the engine warm, all plugs out and the battery charged, cranking each cylinder through several revolutions. Absolute numbers vary by engine family, so consistency across cylinders matters most: variation within roughly 10% is normal, and a cylinder well below its neighbors is a finding, not a footnote.
A low cylinder redirects the inspection rather than ending it. Next is a leak-down test to locate where the pressure is going, valves, rings or head gasket, then a borescope through the plug hole to see the piston crown and bore. The camera answers what a gauge cannot: scoring on the bore, a washed-clean crown suggesting a lean run, detonation damage, or corrosion inside a cylinder that took water. Results are recorded cylinder by cylinder, giving the buyer a baseline for the rest of the engine's life.
The sea trial is where the engine stops hiding
An engine at the dock idles; an engine under load reveals itself. The trial runs with normal load aboard and the laptop connected, on live data rather than dash gauges.
Recorded: cold-start behavior, idle quality in and out of gear, shift engagement, wide-open throttle RPM against the maker's rated range, operating temperature from the ECU, charging voltage under way, trim under load, vibration, smoke at trolling and cruise, any code thrown during the run, and hot-restart behavior. WOT RPM is the most informative number on the trial: an engine that cannot reach its rated range is either over-propped or down on power, and the difference is a propeller versus a powerhead. Anything found under load is written up the way a standard diagnostic finding is, with the cause named.
Corrosion and impact damage: where the money hides
Salt-water outboards fail from the outside in, and the evidence sits where a walkthrough does not reach. The cowl comes off, and the powerhead, harness, connectors and exhaust adapter are inspected for corrosion and salt tracks.
An engine inspection is not a marine survey
These are two professionals doing two jobs, and a used-boat buyer generally needs both. Hiring one and calling it the other is the most common mistake buyers make.
| Pre-purchase engine inspection | Full marine survey | |
|---|---|---|
| Performed by | Marine mechanic | Accredited marine surveyor |
| Covers | Engines, rigging, controls, propulsion, ECU data, sea trial | Hull, stringers, transom, coring, moisture readings, structure, systems |
| Accepted by insurers and lenders | No | Commonly required |
AquaRepair Marine does not perform hull surveys and does not represent this inspection as one. A hull surveyor should be engaged alongside, usually on the same haul-out and sea trial day. Warranty questions on a boat still under coverage go to the brand's dealer network.
Book a pre-purchase inspection
FAQs
Do I need a full survey as well? For most purchases, yes. A survey by an accredited marine surveyor covers hull, structure, moisture and systems, and it is what insurers and lenders commonly require. An engine inspection covers the mechanical package, where most post-closing cost lives on an outboard boat. The two are usually scheduled around one haul-out.
Will the report tell me what to offer?
What if the seller will not allow a sea trial? Worth knowing before spending money. Much of the inspection, ECU hours and history, compression, corrosion, gearcase testing, can be done without running the boat and is still worth doing. But behavior under load is not observable at the dock, and a seller unwilling to run the boat has told you something about the transaction.