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What to Expect at a Sea Trial

Introduction

A sea trial is a test sail or motoring run carried out before finalising the purchase of a boat. It is your opportunity to verify that the vessel performs as described, that its systems work correctly under real conditions, and that there are no handling problems that would only become apparent once underway. Alongside the marine survey, the sea trial is one of the most important due diligence steps in the boat buying process.

When Does the Sea Trial Happen?

The sea trial typically takes place after you have signed a Purchase and Sale Agreement (PSA) and paid a deposit, but before the final payment is made. The PSA should explicitly state that the purchase is subject to a satisfactory sea trial. This protects your deposit — if the boat fails the sea trial, you are entitled to withdraw and recover your deposit in full.

In practice, the sequence is usually:

  1. Sign PSA and pay deposit
  2. Marine survey (haul-out inspection)
  3. Sea trial
  4. Negotiate based on findings (if necessary)
  5. Final payment and transfer of title

Who Attends the Sea Trial?

At minimum: you (the buyer) and the seller or their representative. You should also invite:

  • Your marine surveyor — Many surveyors include sea trial attendance as part of the pre-purchase survey fee. They will observe engine performance, listen for mechanical issues, and test systems with a professional's ear and eye.
  • A trusted experienced sailor or engineer — If you are a novice buyer, having an experienced friend present is invaluable.
  • Your yacht broker — If you have one, they should be present to document the trial and protect your interests.

The seller or their captain will usually operate the boat during the trial, though you should have the opportunity to take the helm.

Preparing for the Sea Trial

Before you go afloat, do a brief walk-round with the seller:

  • Confirm that the fuel and water tanks are adequately filled.
  • Check that all safety equipment is accessible and in place.
  • Ask the seller to explain any unfamiliar systems or controls.
  • Take photos of the instrument readings before departure (engine hours, fuel level).
  • Bring a notepad or use your phone to log observations during the trial.

Engine Start and Warm-Up

Observe the engine start carefully:

  • How does the engine start? Does it fire promptly, or does it struggle?
  • Listen for unusual noises immediately after start — rattles, knocking, or excessive smoke.
  • Check the exhaust: a small amount of white smoke at cold start is normal for diesel engines and should clear quickly. Black smoke indicates over-fuelling; blue smoke indicates burning oil.
  • Check that oil pressure and temperature gauges rise to normal operating range within a few minutes.
  • Allow the engine to reach operating temperature before putting it under load.

Leaving the Berth

The departure manoeuvre reveals a lot about the boat's handling and the condition of its propulsion system:

  • Does the engine engage smoothly into forward and reverse?
  • Is there any vibration through the hull at low RPM? (Could indicate propeller damage or shaft misalignment.)
  • Test the bow thruster if fitted — it should move the bow smoothly without unusual noise.
  • How does the boat respond at slow speed in a crosswind or current?

At Sea: Engine Performance

Once clear of the harbour, the seller should demonstrate the engine across its full RPM range:

  • Gradually increase RPM from idle to maximum rated RPM.
  • At maximum RPM, the boat should reach approximately its rated maximum speed. Note the actual speed on the chart plotter.
  • At cruising RPM (typically 70–80% of maximum), note the speed and fuel consumption if an instrument is available.
  • Listen throughout for mechanical changes in engine noise — a change in sound can indicate a developing problem.
  • Check the exhaust throughout: it should remain clear at operating temperature.
  • Watch engine temperature — it should stabilise within the normal operating range and stay there.

Run the engine at cruise speed for at least 30 minutes. Problems with cooling, fuel delivery, or overheating often only emerge after sustained use.

For Sailboats: Testing Under Sail

Insist on hoisting the sails and sailing the boat, even in light conditions:

  • Hoist the mainsail — observe how it comes up the track. Check for stiff or missing slides, battens, and leech line condition.
  • Unfurl the headsail — does the furling drum operate smoothly? Is there any binding or stiffness?
  • Sail on both tacks — observe how the boat balances. A well-tuned boat should sail on a slight weather helm in moderate breeze. Excessive lee helm is a handling concern.
  • Tack and gybe — test how the boat handles sail changes. Observe the traveller, mainsheet, and winches in operation.
  • Check instruments under sail — wind speed and direction, boatspeed, and depth should all read correctly.
  • Test the autopilot under sail — it should hold course without hunting or excessive rudder activity.

If the seller is reluctant to hoist sails or insists conditions don't allow it, be cautious — this is a key part of the trial for any sailing vessel.

Systems Checks Underway

While the boat is underway, methodically test all onboard systems:

  • Chart plotter / GPS — confirm it is tracking position correctly and displaying charts.
  • VHF radio — switch to a working channel and test transmission and reception.
  • AIS — confirm targets are being received on the chart plotter display.
  • Radar — if fitted, power it on and confirm it is painting returns.
  • Depth sounder — check it is reading correctly against charted depth.
  • Navigation lights — switch on and visually check all are working.
  • Windlass (anchor winch) — run it up and down under light load.
  • Generator (if fitted) — start it and check that 230V power is available.
  • Bilge pumps — test both manual and electric; check that the automatic float switch activates correctly.

Returning to the Berth

The return to the berth is another test of the boat's slow-speed handling:

  • Observe how the boat responds in reverse — some boats are difficult to steer astern due to propeller walk.
  • Watch for any hesitation when shifting from forward to reverse under load.
  • After docking, inspect the bilge — any water that shouldn't be there?
  • Check the engine compartment after shutdown for any signs of new leaks (oil, coolant, fuel).
  • Take a final reading of engine hours.

What to Do If You Find Problems

Not every issue discovered during a sea trial is a dealbreaker. Minor findings can be addressed through price negotiation. However, the following should be taken very seriously:

  • Engine overheating or failure to reach rated RPM.
  • Excessive vibration suggesting shaft or propeller damage.
  • Gearbox that fails to engage or slips.
  • Significant water entering the bilge while underway.
  • Major electrical failures.
  • Rigging that is visibly unsafe (broken wire strands, cracked swage terminals).

If you discover serious issues, you have the right to withdraw from the purchase under the terms of your PSA and recover your deposit.

Sea Trial Checklist Summary

  • ✔ Observe cold engine start
  • ✔ Check exhaust colour throughout
  • ✔ Full RPM range test — note speed achieved
  • ✔ Sustained cruise at normal RPM for at least 30 minutes
  • ✔ Hoist sails and sail on both tacks (sailboats)
  • ✔ Test all electronics underway
  • ✔ Test navigation lights, bilge pumps, windlass
  • ✔ Observe handling at slow speed and in reverse
  • ✔ Inspect bilge and engine bay after return
  • ✔ Log all findings — photos and notes