What the inspection covers
Think of it as a mechanical and electrical once-over on a boat that isn't yours yet. The engine goes first. How does it start cold? How does it idle? Oil level and condition, cooling flow, belts and hoses, fuel lines and the primer bulb, the battery and what the charging puts out under load. Then the drive: gear lube, prop and prop shaft, trim and tilt, and whether it stays where you set it. Nothing taken on trust. Nothing judged off the listing photos.
Most of the value is in what a seller has no reason to mention. A trim ram that weeps. A steering cylinder with a torn boot. Corroded ring terminals behind a battery switch. A bilge pump wired through a float switch that doesn't float anymore. None of that stops a boat leaving the dock for a ten-minute demo ride, and every bit of it costs money once she's yours. It all gets written down, so you're not relying on your memory of a busy afternoon.
Where a mechanical inspection stops and a surveyor starts
This isn't a marine survey. A survey, done by an accredited marine surveyor, is a different paper for a different reader. It's about value and condition, for an insurer or a bank, and it usually means the boat comes out of the water for moisture readings across the hull and a structural look at stringers, bulkheads and coring. Older or higher-value boat? Insurers and lenders will often insist on one. Need financing? Need a policy written? Is the boat big and old enough that structure's the real question? Then get a survey.
A mechanical inspection answers a narrower question, and answers it really well: does the powerplant and everything bolted to it work, and what'll it take to fix what doesn't? On a twenty-foot bowrider with a known engine, that's usually the whole question. The two don't compete. Buyers of bigger boats often book both, and the mechanical findings tell the surveyor where to dig harder.
Compression, gear lube and the story fluids tell
Compression is the least expensive look inside an engine you'll get. Don't fixate on the number itself — what tells the story is how far apart the cylinders are. All in a tight band? Even wear, probably. One sitting well below the rest? Could be a ring, a valve or a scored bore, and that's when you stop and find out, not start haggling. On a four-stroke, check the oil while you're at it. Milky, overfilled, or smelling of fuel changes the whole conversation.
Gear lube is the other tell. Drain some into a clear jar and hold it up. Good lube, you can see through it. Water turns it cloudy gray, coffee with milk, and if there's glitter in it, that's metal off the gears or bearings. Water in a gearcase almost always points to a failed prop-shaft or driveshaft seal — and that tells you something about the seller as well as the boat. Nobody looked after a lower unit that ran a whole season wet.
Electrical, hull and transom
For the electrics, follow the current. Batteries get load-tested, not just read sitting there. Terminals come off and get a look. The main switch and fuse block get checked for green corrosion and scorch marks, and the charging output gets read at the battery with the engine running. Then you flip on every circuit — nav lights, blower, horn, pumps, trim, gauges, electronics. The trouble's usually in whatever wiring past owners tacked on over the years, and once you've seen a factory loom, you can pick that out in a second.
Above the waterline, the transom and hull get every check you can do without a lift. Flex in the transom with the drive trimmed. The seal around the transom assembly, or the outboard bracket bolts. Little stress cracks at the corners. Water stains in the bilge and under the deck hatches. Soft spots when you walk around. The bottom itself — the running surface, the keel and strakes, anything fitted below the boot stripe — needs the boat out of the water. If that matters to the deal, get it hauled before you pay.
The water test, and what you are handed at the end
A boat that runs on a flushing attachment in a driveway has told you almost nothing. Load is what shows the problems. An engine that only overheats when it's worked. A drive that won't hold trim. Fuel trouble that only shows up at wide-open throttle; a gearcase that whines under power; a hull that porpoises because the prop's bent. A water test puts the engine under real load across its whole range, a hole shot and a long run at cruise included.
Why that matters here: the calendar. Most private sales around Lake Winnipesaukee happen in a short window either side of ice-out, on a boat that last ran in October and has sat on a trailer or under shrink wrap since. Ice-out in 2026 was declared on April 13, and across the record the average has moved earlier, from roughly April 23 towards April 14. Before that date there's nowhere to test it. So a boat sold in March is sold on an engine nobody's heard run under load.
If a water test truly can't happen, that's not automatically a reason to walk. It's a different risk, though, and it should be named and written down as one. What you get is a written record: every item checked and its condition, photos of anything wrong, and a plain split between ordinary wear, repairs to plan for, and findings bad enough to walk away over.