Why Are Boat Engines Measured in Hours?

Every time you see someone in a boat on the lake, river, or in the ocean, that little green envy monster starts rising up and you wish it was you out there. Next thing you know you’re at the local boat show, looking at gently used boats. There are a lot of new terms to learn, like this new usage of the word “hours.”

Why Are Boat Engines Measured in Hours?

Why are boat engines measured in hours? Boat engines, much like heavy equipment engines, operate under a different kind of strain and are used in a much different environment than an automobile engine. Keeping track of the number of hours the boat’s engine has been running is key to making sure that routine maintenance happens at an interval that will keep the engine running at an optimum level.

Most times, boats are fitted with a running hours meter. If the boat you’re looking at doesn’t have an automated measuring method, the captain will certainly have a detailed engine log. Let’s look at how these numbers vary based on the type of engine your boat has.

The Hours of Diesel versus Gasoline Boat Engines

Before we even start to talk about how many hours of use an engine can usually safely run until standard maintenance is needed, let’s talk about the difference between gasoline and diesel engines.

Boat Size Matters

In some cases, by starting with asking the boat’s length, you can eliminate the gas vs. diesel question.

• Smaller boats on the market (up to 35 feet) typically only offer gasoline options.
• Larger boats over 45 feet in length generally won’t have an option other than diesel.
• Boats in the 35-45-foot length range will offer the choice of gasoline or diesel.

Gasoline Engines

If you have a smaller boat, a gasoline engine will have the power you want to get you moving. Gasoline engines are also significantly quieter than their diesel counterparts.

Gas-powered engines typically need to have major maintenance performed every 1,500 hours. Of course, just as you would on your car or truck, you’ll want to conduct annual spark plug, oil, filter, fluids, and water pump impeller inspections and maintenance to keep everything running smoothly.

Diesel Engines

Diesel engines tend to be heavier, stronger, have better fuel efficiency, noisier, and much more expensive than their gasoline counterparts. They are also perceived to be safer, but that is assuming they are being used properly, and timely maintenance is performed.

The average diesel boat engine can go about 5,000 hours between servicing. They used to be able to go significantly longer than that before needing a major overhaul (up to 8,000 hours.) That is not necessarily the case any longer. The addition of the turbocharger has put much more strain on the diesel engine – boaters want to go faster and to generally have more power.

A captain that doesn’t over-tax his turbocharger can still expect to see a much higher number of hours usage before the engine needs to be replaced or rebuilt. That said, it isn’t uncommon for a diesel engine to cost in excess of $20,000 more than its gasoline-powered cousin.

One other point for diesel engines is that diesel’s flashpoint is much higher than that of gasoline. This means that gasoline can explode earlier than diesel. Not really something you want to think about, but it becomes a serious safety concern when considering the pros and cons of the two types of engines.

Knots versus Miles

Something else to consider when wondering why boat engine life is measured in hours is to consider that a nautical mile is not the same as a land-based mile. A nautical mile is, in general, 1.15 miles for every land (statute) mile.

It’s also important to think about the impact that currents have on the stress, wear, and tear of a boat’s engine.

Yes, it’s true that if your car is battling a headwind, your gas mileage will be worse than if you weren’t. That said, currents, swells, and waves require more from your boat’s engine than the wind does on its regular land counterpart.

Life Expectancy of a Boat’s Engine

We already discussed the fact that gasoline engines will run about 1,500 hours and diesel about 5,000 before needing major work done. That’s fine, but what does that really mean when talking about how long you can use your boat until you need to plan for an engine overhaul?

One preventative step you can take is to know that short running time between stops and long idle times are hard on your boat’s engine. These practices can lead to the need for earlier repairs.

Let’s think about a typical recreational day on the water.

• Getting out of port (or off the dock) and out to open water.
  • 30 minutes
• Motoring around a bit to feel the wind on your face; then you’ll go to the spot where you want to spend some time fishing or swimming or sunbathing and will drop anchor.
  • 1 hour
• Spend some time pulling water skiers or tubers and then drop anchor again.
  • 1.5 hours
• Motor back to the dock (or pier).
  • 1.5 hours

So, for this particular day’s worth of fun, you’ve probably used about 4.5 hours of engine time. Some trips will use more time; many will use less.

Let’s assume you live somewhere you can go out every weekend, and you’re on the water every Saturday and Sunday – it’s highly unlikely, but it could happen.

That’s 104 days or approximately 468 hours of engine use.

That would mean you would need to consider a gasoline engine overhaul in about three years. You’d have about 10 years for a diesel engine.

Some of the additional factors that impact your engine’s performance are:

• The presence of saltwater
• How clean and dry you keep the bilge
• How often you perform needed routine maintenance

The Best Environment for Your Engine Compartment

To preserve your engine’s life, paying close attention to your boat’s engine compartment will work in your favor.

Engine compartments should have plenty of dry, cool (about 50 degrees Fahrenheit), clean air. To accomplish this, compartment blowers should always be set to exhaust and should run for at least 5 minutes before you start your boat’s engine.

Just as an airplane pilot has a pre-flight check, you, as the captain of your boat, will want to have a pre-launch check.

The Pre-Launch Oil Check

Performing simple tasks such as checking the oil before you leave can provide you important information.

• Check the oil level and appearance. If there’s a higher level of oil than you expected, and it has a somewhat milky appearance, you may need to check to make sure water didn’t find its way into your engine. Less oil than you expected could mean you have a leak somewhere.

There’s nothing worse than getting to the middle of the lake and having your engine seize up. That is unless you’re like one poor captain who got to the middle of the lake and had his brand-new trolling motor fall off because it hadn’t been properly mounted. Those make for dark days.

In Conclusion

Boat engines are measured in the number of hours they’re physically in use as opposed to the number of miles they can be expected to travel. Time is a better metric for how much wear and tear an engine is taking.

So, whether you decide on gasoline or a diesel engine, conduct your pre-launch checks and we wish you fair winds and following seas.