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Sea trials - Putting a boat through its paces

Putting a boat through its paces on the water can reveal a lot

Putting a boat through its paces on the water can reveal a lot about its design, systems, performance and more

During the course of numerous sea trials, I have uncovered various issues aboard boats of every size and configuration, some being mechanical in nature, others emanating from questionable design or manufacturing practices, and still others due simply to the lack of routine maintenance.

Read the other stories in this package: Sea-trialing a displacement hull  

For example, a recent test run aboard a repowered Boston Whaler Revenge revealed the fact that although the engines were new, correctly sized and installed by an authorized dealer, the rigging hadn’t been done properly. The boat wouldn’t handle or perform anywhere close to its potential, leaving the prospective buyer to question the vessel design.

He eventually located and purchased an identical boat that had been properly set up, and exhibited none of the handling issues of the first.

On a Kadey-Krogen yacht I surveyed in Florida, the conventional stuffing box had been replaced with an aftermarket “packless” unit; the owner said the original required “excessive maintenance.”

During the sea trial I observed the newly installed dripless system spewing water, as well. It turned out that the running gear was misaligned to such a degree that it would have been impossible to maintain watertight integrity through the shaft log.

Every vessel can benefit from a periodic evaluation under power, commonly referred to as a sea trial. This story will focus on planing powerboats, although much of the information also will apply to displacement hulls. (See companion story on displacement boats.) My hope is that, by reading this, you will be able to better evaluate your next boat purchase, or if hiring a professional surveyor for the job, make you aware of what that person should and will be critiquing.

A sea trial is a critical part of evaluating a vessel’s performance, machinery, controls and systems, in addition to its comfort and safety. When carefully performed, the sea trial will demonstrate the handling characteristics of a boat and provide valuable information regarding the operating systems, such as engines, their cooling and exhaust systems, steering, running gear and most of the installed equipment aboard the boat. Consideration also is given to structural elements of the hull, deck and overall construction.

I use the sea trial to determine if any undesirable characteristics exist, such as not reaching advertised speed, instability, poor steering response, underpowering or failure to trim. Although the nature and duration of a sea trial are determined by the vessel’s intended use (offshore, coastal, etc.) and other considerations, I make every attempt to put each boat through similar testing and evaluation. The more exhaustive the sea trial, the more likely that hidden faults will be revealed.

When practical, it’s best to put the boat through its paces in reasonably windy and bumpy conditions to avoid post-delivery disappointment with the boat’s rough-water handling and safety. Not all issues or questions that arise during a sea trial are critical; some are just good to know about. You also want access to protected waters for the sea trial.

It should go without saying that the boat needs to be fully commissioned, reliable and ready for the sea trial, but I have spent many an afternoon sitting on the dock waiting for batteries to charge, tanks to be filled, and spark plugs to be changed. I review vessel preparation with the seller or broker several days prior to the sea trial, and confirm the day before. Fuel and water tanks should be a least half full, though I prefer them to be topped off. With older fuel tanks in particular, running in rough water with full tanks can reveal leaks that otherwise might not be obvious.

The question as to who should operate the boat during the sea trial is constantly debated among professional surveyors. There are numerous observations that can be made only while operating the boat, but much of what needs inspection should be accomplished with someone else at the helm.

When I sea trial a boat, I have the vessel owners or their representative handle the close-quarters maneuvering, both dockside and in restricted waters. I ask him or her to perform several maneuvers when they feel it is safe to do so.

Once the boat is in open water, I request the helm and take over for my testing. Only after getting a good feel for the vessel will I attempt any close-quarters maneuvering. I strongly suggest limiting the number of participants on board to only those necessary for the sea trial. Hatches will be open, abrupt and sudden maneuvering will occur, and you need to be able to move about freely. Before leaving the dock, quickly inspect the interior and exterior of the boat, being certain that everything is stowed and secured.

At the dock

I like to begin the sea trial with cold engines, because cold starting can reveal conditions that can go unnoticed after the engines are warm. For example, slow cranking can be caused by battery or electrical-connection issues, and difficult starting can be a sign of faulty ignition or fuel systems.

With inboard, sterndrive and V-drive boats, I place a plastic drop cloth (an old picnic table cover works well) under the engine. Inspected following a hard run, it can indicate even the most minor engine oil, transmission or coolant leaks that may otherwise go undetected.

Note the level and color of the engine oil and coolant for comparison after the sea trial. An increased oil level and milky appearance indicate the presence of water in the oil, possibly caused by a leaky head gasket, or cracked engine block or cylinder head. An abnormal increase in the coolant level can indicate the presence of seawater in the closed-circuit cooling system, signifying a failed heat exchanger. A decrease in coolant could point to a bad cylinder head gasket, allowing the coolant to be turned into steam within the cylinder.

Note the engine hours prior to starting, then check again following the sea trial to confirm the hour meter’s operation and accuracy. Move the throttle and shift controls to confirm smooth, easy operation. There should be a positive mechanical detent enabling you to feel where neutral is located. (If not labeled, confirm which lever controls which function. I have been embarrassed on more than one occasion by linkages set up in different sequences.) The controls should remain set where you place them, without creeping.

Turn the ignition on without cranking the engine; the engine alarms should activate in a few seconds, confirming proper operation. On multiple-engine boats, start one engine and let it settle down to idle before proceeding to the second. This will enable you to isolate any abnormal mechanical sounds while observing the color of the exhaust smoke, and confirming the flow of cooling water from the exhaust.

Black exhaust smoke on engine startup or while running is caused by a rich mixture (excessive fuel), which normally can be corrected with a comprehensive tuneup. Blue smoke that appears to linger and settle on the water surface can be caused by oil leaking past the valve guides or piston rings. It isn’t uncommon for there to be a slight blue tinge to the exhaust of older engines with high operating hours; however, an engine survey might be in order.

By this time the oil pressure and charge indicators should provide stable readings. I shut the first engine down while starting the second, allowing unhindered observation of the second power plant. Once the second engine has settled down, restart the first engine and allow them both to warm up. The engines should run identically, and comparative gauge readings at the helm should be similar.

Many larger vessels have second helm stations, and a few have cockpit controls. Be sure to check all controls and instrumentation at each station.

Once the engine is running, I turn on all electronics, navigation lights and any equipment that can be used while the vessel is under way. This not only verifies their operation, but should apply a load to the charging system as well.

Listen for squealing alternator belts and growling alternators, which can indicate the charging system needs attention. Observe the helm-mounted charge indicator for system voltage. I monitor the circuits periodically during the sea trial, and again after returning to the dock. Ask about the operation of any electronics you are unfamiliar with — the autopilot in particular, as it should be tested during the open-water portion of the sea trial.

Observe the level and condition of the bilge water, looking for signs of fuel, oil or coolant. I carry white index cards to dip into the bilge as an aid in determining what is floating on or mixed with the seawater. Checking again after the sea trial can provide another indicator of engine/transmission leaks or excessive seawater coming in through packing glands.

If practical and safe, I leave the engine hatches secured open. If the hatches are removable, I might leave them at the dock to provide additional deck space. In protected waters, I often remove the outboard cowlings for a period of time. Once the boat is under way, the open hatches will allow you to monitor the machinery for leaks and vibration and, with the use of an infrared temperature gun, confirm the helm instrument readings. In addition, I use a remote photoelectric tachometer to confirm engine rpm.

On the water

As the vessel operator shifts between forward and reverse leaving the dock, observe the prop shaft/coupling interface of inboard and V-drive boats. There should be no movement between the two. A shaft that is loose will almost invariably show up as it slides in and out of the coupling.

Evaluate operation of the engine and transmission controls, and note any uncertainty about shifting or neutral idle problems, especially in sterndrive and outboard boats. The engine should idle smoothly and within specified rpm with the vessel in gear, and be able to remain at idle or slightly above for close-quarters maneuvering. (Vessels equipped with powerful diesels that swing large props may require trolling valves to maintain close-quarters maneuverability.) With this simple test alone, I have discouraged prospective purchasers from continuing with the sea trial, based on an engine misfire or difficulty with shifting.

As you leave the dock, confirm that the trim tabs are fully retracted. The boat should track straight, both at idle and cruise speeds. (With twin-screws, be certain that both engines are running at the same rpm.) Excessive play in the steering system linkage or rudder misalignment will cause the boat to wander or snake from side to side. Veering to one side usually is indicative of rudder misalignment, but it also can be caused by too many through-hull fittings on one side of the boat or a hull that’s asymmetrical. Boats with propeller pockets or tunnels aren’t known for responsive steering at low speed. Their undersized rudders can make docking a challenge, and care should be taken in any difficult seaway.

While running in protected waters, I inspect the stuffing box and rudder packing for excessive leakage. There should be no vibration in the deck, and the prop shaft should be running true. Prior to any high-speed runs, I evaluate and record overall performance and handling characteristics through a range of speeds, normally in 500-rpm increments. Conditions permitting, I run the boat up-sea, down-sea and with the waves on the beam to determine the boat’s handling characteristics. On a calm day, you may need to double back over your own wake.

For the steering to be responsive, there should be no more than three or four turns from lock to lock. I perform a series of decreasing-radius turns at various throttle positions, both to port and starboard. I accelerate and decelerate from these turns, as well. The water will get fairly confused, which is part of the goal. Look for excessive roll or heel, nose diving, catching a chine during turns, porpoising, or any condition that affects the balance and handling of the vessel. Determine if the cockpit would be safe and comfortable for passengers, and if it has adequate freeboard and hand-holds. The transom door should remain latched during the exercise. I have seen poorly designed latches come undone as the boat flexes during a hard turn.

With the boat running straight again, I do a series of short turns to simulate quick, evasive maneuvering by rotating the helm a quarter-turn in each direction. By this time you should have a good idea of the boat’s handling characteristics. At this point I return the helm to the skipper and ask that the vessel be accelerated up on plane. Things can occur rapidly, so this procedure may need to be repeated a few times. While the vessel is accelerating, I observe how the bow rises and note the visibility over it. I carefully listen to the engine; it should remain smooth and strong without hesitation or misfire. It shouldn’t speed up rapidly — an indicator of prop slip — but should be in sync with the hull speed.

The boat shouldn’t require full throttle or, in my opinion, trim tabs to get up on plane. Once on plane, you should be able to back off the throttle slightly without the boat falling off. Observe the engine instruments and note their readings for future analysis. Again, visually check the machinery for any leaks. If the instrumentation indicates everything is stable, ask that the boat be brought up to full throttle and run for a minute or two. Using an infrared temperature gun, I scan the engine heat exchangers, oil coolers, exhaust risers and elbows for temperature anomalies. I also check the temperature of the stuffing box and transmission.

Determine if the engine is turning at the correct rpm, based on the manufacturer’s specifications. Twin engines should run up to wide open throttle and synchronize. If not, bring the fast engine down to the slower one and determine the difference. Most V-8 gas inboards will turn between 4,000 and 4,400 rpm at WOT. Low-speed diesels typically are governed to 2,500 rpm, and should be within 50 rpm of that figure. High-speed four-cycle diesels can turn between 2,800 and 3,400 rpm, and should be within 100 rpm of the manufacturer’s recommendation. Diesels shouldn’t be allowed to over or under rev.

Slowly back off full throttle and allow the boat to settle back to cruising speed. Observe the exhaust and look for color indicators, as when starting the engines, being careful of the station-wagon effect in the cockpit. While at cruising speed activate the trim tabs one side at a time to confirm proper operation by the change in hull trim and vessel heading. Also, go below and open doors, lockers and drawers. Examine partitions and bulkheads for anything that may be binding or excessively loose. As the hull flexes, clearances may change between the panels; excessive clearance or binding can indicate too much hull flex.

Any vibration seen or felt on the flybridge or in the forward quarters while at cruising speed is excessive and damaging. All boats will vibrate through some portion of their rpm range, but should not do so constantly. Most vibration issues I encounter are caused by excessive shaft runout, which I define as the degree that the prop shaft runs off center. This can be caused by misalignment of the struts, stuffing box, engine and transmission, or an out-of-balance propeller or worn cutless bearings, among others.

The last test I perform is the back-down test. By accelerating an engine hard astern and then hard forward, the integrity of the engine-mounting system can be assessed. I carefully demonstrate the procedure to the skipper, and if we are comfortable with the operation, I observe the engine-mounting system while he or she operates the boat.

To start the back-down test, place the engine in reverse gear and briskly open the throttle about halfway as the boat moves aft. As soon as the boat is making way, close the throttle, select forward gear and open the throttle again. There should be no play where the engine mounts attach to the beds, stringers or engine. The flexible rubber portion of the engine mount should allow for up to 1/8 inch of movement.

Heading back in

If possible, I like to do close-quarters maneuvering while returning to the dock. It provides me with a final opportunity to confirm equipment operation and monitor instrumentation. Once back at the dock remember to recheck the engine oil level and condition, coolant level, and bilge water volume and content with a fresh index card prior to leaving the boat. Although I take notes during a sea trial and review them before leaving the boat, I find that — barring any glaring issues — I can provide the most accurate evaluation of the vessel immediately following my trip home in the car, when information, observations and impressions are still fresh.

Many issues uncovered during a sea trial are relatively minor, and can be attended to by competent technicians. However, there may be design issues with a particular vessel that require you to decide what compromises you are willing to accept. If in doubt, consult with a professional marine surveyor or repair facility.