Under Load: How to Run a Sea Trial That Actually Tells You Something

There are two watery events in a boat purchase, and buyers routinely blur them into one. The first is the sea trial: a boat, a stretch of water, and a seller trying very hard to look relaxed. The second is the survey: a qualified person with a moisture meter and a hammer telling you what the first event couldn't. They answer different questions. Confusing them is how people end up with a lovely-handling boat and a rotten transom.

An audition, not an inspection

Think of the sea trial as a test drive with consequences. It tells you how the boat sits, sounds, steers and stops. It tells you whether the engine makes its numbers. It gives you a feel for whether you actually want the thing. What it does not do is look inside the hull, pull the leg apart, or tell you the standing rigging is three seasons past sensible. A trial is a snapshot taken on one day, in one weather window, with an engine that has usually been run recently. Treat it as evidence, not as a verdict.

Sort the order of play before you commit

Most brokers will happily arrange a trial, but the details matter. Ask for the trial to happen before the survey if you can, or on the same day with the lift-out straight afterwards. That way a gearbox that won't hold pressure under load can be fed straight into the survey conversation while the boat is still on the hard.

Agree a few things in writing first: who pays for fuel, whether a mechanic can attend, what happens to your deposit if the trial throws up something serious, and whether you're allowed to handle the boat yourself. Some sellers want to keep the helm. That's understandable, but you need at least ten minutes of your own hands on the wheel and throttle. If the answer is a flat no, ask why.

Also ask the seller, politely and firmly, not to start the engine before you arrive.

The cold start is half the story

Turn up early. Before anyone touches a key, have a look at the coolant level, the oil, the belts, and whether there's a suspiciously fresh rag under the engine. Then start it cold, from genuinely cold, and watch.

You're listening for how quickly it catches, whether it hunts or stumbles for the first thirty seconds, and what comes out of the exhaust. Blue smoke that clears is one thing. Blue smoke that lingers, or white smoke that never settles, is a conversation. A diesel that needs a whiff of throttle to fire on a mild November morning is telling you something about compression or glow plugs.

An engine that's been warmed up for you before arrival is a small red flag. Not proof of anything, but a seller who wants to hide a rough start usually has a reason.

Now put it under load

This is the part that gets skipped, because it takes time and everyone wants to be back at the pontoon. Don't let it be skipped.

Take the boat out to open water and work through the rev range deliberately. Note the speed at each step. Then take it to wide-open throttle and hold it there for a couple of minutes, conditions permitting, and check three things: does it reach the manufacturer's rated maximum revs, does the temperature gauge stay put, and does anything new start vibrating?

A diesel that tops out well short of its rated revs is either over-propped, fouled, or tired. Any of those is worth knowing before you hand over money. Watch the exhaust under load too, because a prop that's too big for the engine will often show as black smoke that wasn't there at half throttle.

Then drop back to a fast cruise and stay there. This is the speed you'll actually use, and it's where you'll notice a droning shaft, a whining gearbox, or a stern gland dripping faster than it should. Outboard owners should glance back at the telltale stream periodically; a weak pee at cruising revs is a cooling issue waiting to be expensive.

Slow, tight and awkward

Handling gets tested in two places: open water and the marina. Out in the open, do figure-of-eights both ways, feel how the boat leans, and check the trim tabs or outboard trim actually change the ride. Try the autopilot if there is one, and let it hold a course for a few minutes rather than thirty seconds.

Back at the marina, ask for a slow-speed run past the pontoons. You want to hear the gearbox going in and out of gear cleanly, feel the prop walk in reverse, and get a sense of how the boat drifts. Windage is real, and a boat that feels nervous in a ten-knot crosswind on a calm day will feel considerably worse in April.

While you're stationary, run the windlass up and down with the engine on. Drop and raise the anchor. Check the bow thruster. Open and close the seacocks you can reach.

The long list of things water hides

A clean trial tells you the engine started and the boat went forward. It says nothing useful about hull moisture, osmosis blisters, delamination, keel bolts, corroded through-hulls, rudder stock play, cutlass bearings, chainplates, or the age of the standing rigging. It won't find sludge in the bottom of a fuel tank unless you're drawing from the very bottom. It won't reveal a gearbox clutch on its way out if the run is short and gentle. Intermittent electrical faults rarely appear on demand.

A calm day also hides slamming and a following sea, and a half-empty tank hides trim problems. Even the best-organised trial is a couple of hours out of a boat's life.

Keep notes, then get it surveyed

Write down the revs, the speeds, the temperatures, and every noise you didn't like. Ask the broker to confirm the engine hours on the hour meter in writing. If the boat is a significant purchase, have an independent engineer attend rather than relying on the seller's mechanic.

Then book the survey. Ask the surveyor to pay particular attention to anything the trial raised. A sea trial tells you whether you want the boat. A survey tells you whether you should have it. You need both, and in that order.