The sea trial: what to check before, during and after

A survey tells you what condition a yacht is in. A sea trial tells you how she behaves when everything is working at once: engines under load, generators carrying the house systems, steering and stabilisers in a real sea. Many expensive faults only appear under way, or in the first minutes after a cold start.

A pleasant hour along the coast proves very little. This guide sets out what to check before, during and after the run, what your surveyors are doing while you watch, and how the result feeds into acceptance under the purchase agreement.

Before you leave the berth

Insist on a cold start. Ask the seller or broker, in writing and in advance, that the engines and generators are not run before you arrive. A warm engine can hide hard starting, smoke that clears once the engine is hot, and some leaks. If you arrive to find the engine room warm, note it and ask why. Some white or grey smoke on a cold start is normal and should clear as the engine warms; heavy or lasting smoke is not.

Read the logs. Look at the engine and generator hour meters and compare them with the service records and the listing. Ask for the maintenance log, recent work orders and any fault codes stored by the engine electronics. Gaps in the history need answers.

Check fluids and bilges. Before the start, your engine surveyor will usually check oil and coolant levels and condition, look for fuel, oil or coolant in the bilges, and look at belts, hoses, raw-water strainers and exhaust elbows.

Agree the plan. Confirm who is in command (normally the seller's captain or a skipper the seller approves), the route, the duration, the fuel on board, and what tests the surveyors want to run. Make sure the weather and sea state allow a meaningful run.

During the trial

Record readings with the time and engine speed. Your surveyors will take their own notes, but your record helps later.

Engines and drivetrain

• Load and wide-open throttle. The engines should be run up through the range and, where the builder's and engine manufacturer's guidance allows, held at full load for a period agreed with the engine surveyor. The key question is whether each engine reaches its rated maximum speed under load. If it cannot, the cause may be fouled running gear, wrong propellers, an overloaded boat or the engine itself.
• Temperatures and pressures. Record coolant temperature, oil pressure, exhaust temperature where fitted, boost pressure and gearbox oil pressure at several engine speeds. Readings should be stable and similar between engines on a twin installation.
• Exhaust smoke. As a general guide, black smoke under load suggests incomplete combustion (for example air supply, injection or overloading), blue smoke suggests oil being burnt, and persistent white smoke after warm-up can suggest unburnt fuel or coolant in the exhaust. Colour alone is not a diagnosis.
• Vibration and noise. Feel and listen through the hull, in the cabins and in the engine room. Vibration that rises at a particular speed may point to shaft alignment, propeller damage, worn mounts or cutless bearings.

Handling and systems

• Steering. Test lock to lock at low and at cruising speed. Check for play, noise or delay in hydraulic systems, and check the emergency steering arrangement.
• Stabilisers. Test fin or gyro stabilisers under way, and at anchor where the system offers zero-speed stabilisation. Ask for the service history.
• Thrusters. Run bow and stern thrusters in both directions. Note any overheating or cut-outs during repeated use.
• Generators under load. Run each generator with real load on it: air conditioning, galley, water heaters. Check that voltage and frequency hold steady and that changeover between shore power, generators and any battery systems works.
• Autopilot and navigation electronics. Engage the autopilot on several headings and check it holds a course. Test the chart plotter, radar, AIS, depth sounder, compass, VHF and any satellite communications.
• Watermaker, pumps and alarms. Run the watermaker if fitted, test bilge pumps and their alarms, and ask for the fire detection and suppression system to be demonstrated as far as is safe.

Sailing yachts

On a sailing yacht, the sails and rig deserve as much attention as the engine. Hoist and set every working sail, including furling sails, and check their condition and shape. Run every winch, manual and electric, under load. Tack and gybe, check that the furlers and any hydraulic systems work smoothly, and look at the rig under load for movement at the chainplates and mast step. A specialist rigging inspection is often commissioned separately.

What the surveyors do

Your hull surveyor uses the trial to see the yacht working: how she handles, whether there is movement or noise in the structure, whether the bilges stay dry under way, and how the systems listed in the survey perform. Many surveys also include a haul-out on a separate occasion to inspect the hull, running gear and through-hull fittings below the waterline.

The engine surveyor, where you appoint one, concentrates on machinery: the cold start, readings at each engine speed, performance at full load, smoke, leaks and the condition of the engine room during and after the run.

You commission and pay for these surveyors, and they report to you, not to the seller. Our directory of marine surveyors lists vetted surveyors by location, so you can find one near the boat.

After the run

Inspect the engine room straight away. With the engines just stopped, look again for leaks of oil, fuel, coolant or exhaust, for water in the bilges, and for anything that has moved, loosened or overheated.

Take oil samples. Oil samples from engines, generators and gearboxes are best taken while the oil is warm and well mixed, and sent to a laboratory. The analysis can show wear metals, fuel or coolant in the oil and other early signs of trouble. Results can take several days.

Write it down. Record your own observations the same day while they are fresh, and share them with your surveyors so they can be reflected in the survey report. Note anything that did not work, did not reach specification or could not be tested, and why.

How the trial fits into acceptance

Most purchase agreements, including the MYBA Memorandum of Agreement widely used in the Mediterranean, make the sale conditional on the buyer's survey and sea trial. The agreement normally sets out who pays for what, how long the trial may last, and the deadline by which you must give notice.

After the trial and the survey reports, you will usually choose between three outcomes:

1. Accept the yacht as she is.
2. Accept her subject to conditions, such as agreed repairs before closing or a price adjustment.
3. Reject her in the way the agreement provides, in which case the deposit is normally returned on the terms it sets out.

Deadlines in these agreements are strict. If you need more time, for example to wait for oil analysis or a specialist report, ask for an extension in writing before the deadline passes. Talk to your broker, and to a maritime lawyer where the sums are large, before you send notice.

Start your search

When you have a shortlist, browse motor yachts, sailing yachts or catamarans on Yachtxchange, and use the surveyor directory to find independent surveyors near each boat. For more on how a purchase works from offer to closing, see our guide to buying a superyacht in Barcelona.

This guide is general information, not legal or technical advice. Follow your surveyors' recommendations, the engine and builder's guidance and the terms of your own purchase agreement.