Yacht Sea Trial: What to Check Before You Buy

A yacht that idles beautifully at the dock can hide a great deal once the lines are slipped. Vibration that only appears at cruising revolutions, a genset that trips under real load, a stabiliser that will not hold in a beam sea — none of it shows in a still marina. The sea trial is your single opportunity to see the vessel work before your money changes hands, and buyers who treat it as a pleasure cruise rather than a controlled test routinely miss the faults they are paying to discover.

What the sea trial is for in a purchase

The sea trial sits inside the conditional-purchase window, alongside the survey and, on larger yachts, an engine-room and machinery survey. Its purpose is narrow and specific: to confirm that the vessel and her systems perform as represented when they are actually put under load, at sea, in conditions the dock can never reproduce. A signed sale is almost always subject to satisfactory survey and trial; until both are accepted in writing, the buyer retains the right to walk or to renegotiate.

It is not a demonstration and it is not a hand-over. The seller or their captain typically runs the boat, but the day belongs to the buyer's side. The surveyor observes machinery under way, the buyer's representative watches performance against the specification, and every reading is recorded. The distinction matters: a trial run as a sales showcase flatters the vessel, whereas a trial run as an inspection surfaces the problems you are there to find. Insist, in writing, on a trial long enough and hard enough to exercise every major system, not a gentle turn around the bay.

Propulsion and generators under real load

The machinery is the heart of the trial. Engines and generators that sound healthy at idle must be pushed to reveal their true condition, because heat, load and duration are what expose weakness.

• Main engines through the range: run up in steps to full rated power, holding each stage long enough for temperatures and pressures to stabilise, and watch for smoke, alarms, oil-pressure drift or exhaust colour changes under load.
• Wide-open-throttle check: confirm the engines reach their rated maximum revolutions; falling short often signals fouling, propeller pitch issues, a fuel-delivery restriction or tired engines.
• Generators on genuine load: a genset must be tested carrying real electrical demand — air-conditioning, galley, pumps — not idling, since faults appear only when it is worked.
• Return to idle and restart: verify clean idling, a clean re-start when hot, and no unexpected vibration through the shaft line.

Record oil pressure, coolant and exhaust temperatures, fuel burn and revolutions at each stage. These figures, checked against the manufacturer's specification and the survey, are where an experienced surveyor reads the real health of the plant.

Handling, stabilisers and steering

How the yacht behaves under way is as revealing as the numbers on the engine gauges. The trial should deliberately test manoeuvring and motion control, ideally in a little sea rather than flat calm, so the systems are asked to work.

Put the helm hard over both ways at speed and at slow-speed manoeuvring revolutions, and confirm the steering is responsive, free of play and free of hydraulic groans or leaks. Exercise the bow and stern thrusters repeatedly — they should hold their bite without overheating or cutting out on thermal protection, a common fault on tired units. If the yacht carries stabilisers, whether fin or gyroscopic, test them both under way and, where fitted, at zero speed at anchor: they should visibly damp roll and hold it, without hunting, warning alarms or hydraulic complaint. Note the turning circle, any list in a hard turn, and how the hull tracks at cruising speed. A vessel that wanders, lists oddly or refuses to settle is telling you something the specification will not.

Systems to test: the checklist

Beyond propulsion and handling, a long list of secondary systems must be exercised while there is power, way and load. The table below sets out the core systems, what a satisfactory result looks like, and why it matters to the deal.

Who attends, and documenting the results

The right people in the right roles turn a pleasant day afloat into usable evidence. A serious trial is attended by an accredited marine surveyor, whose job is to observe the machinery under way and read it against the survey; the buyer or the buyer's representative, watching performance against the specification and the broker's representations; and the vessel's captain and crew, who run the boat and answer for how she is operated. On a larger yacht an independent engine surveyor may attend the machinery specifically.

Documentation is what gives the trial value after the fact. Every reading — revolutions, temperatures, pressures, fuel burn, speed at each stage — should be logged, with photographs and, where useful, video of any fault as it occurs. A written trial report, cross-referenced to the survey, becomes the factual record that supports whatever you decide next. A trial with no paper trail leaves you arguing from memory; a trial with a full log lets you negotiate from evidence.

How the findings reshape the deal

The trial rarely ends in a clean pass or fail. More often it produces a defect list, and the value of the day lies in how you use it. Because the sale is conditional on a satisfactory trial and survey, findings give the buyer real leverage that evaporates the moment the conditions are accepted.

• Price adjustment: quantified faults — an engine short of rated revolutions, a failed stabiliser, tired air-conditioning — support a reduction reflecting the true cost of putting them right.
• Repair before completion: require the seller to rectify defined items, verified on a re-trial or by the surveyor, before funds are released.
• Escrow retention: hold back part of the price against work to be completed, released on proof.
• Withdrawal: if the findings are serious enough, the conditional structure lets you walk with your deposit intact.

The discipline is to price the defect list honestly against professional estimates, then choose one route deliberately — not to accept vague reassurance that a fault will be sorted later. Leverage exists only while the conditions stand; use it, in writing, before you sign them away.