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Marine Motors: Challenges & Opportunities

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On the popular British automotive television program “Top Gear,” the hosts were interested in discovering how hard it could possibly be to build a vehicle that was capable of both being driven on the road and sailed in water. Various types of such vehicles have been dreamed about, designed and even occasionally produced over the years, but as we’ve seen, none has really captured the public’s attention.

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After converting a Triumph Herald convertible, Volkswagen camper and Toyota pickup into a bizarre armada of “sailing vessels” the three Brits learned just how much of a challenge it is to create something that could get you around comfortably in city traffic and let you enjoy a day on the bay as well.

How difficult was it? In a word, very.

Despite our dreams and their best efforts, turning a roadworthy car into a seaworthy craft is not as simple as we were shown in old cartoons and James Bond movies.
And in a sense, it’s what the engine rebuilding industry discovered about the marine market as well.


According to one leading engine remanufacturer, marine motors seemed like a no-brainer.
“All of us engine builders looked at the marine market about 15 years ago or so and said, ‘Heck, if we can build an engine for a car, we can certainly build one for a boat.’ We all decided to do that – and we all rapidly learned to fail. Despite the commonality of being internal combustion engines based predominately on domestic automotive engine platforms, we discovered that there are some significant differences between a car engine and a boat engine…and those differences were important.”

Marine Market Facts

According to the National Marine Manufacturers Association (NMMA, sort of the SEMA of the high seas), recreational boating continues to be a major consumer goods industry. The number of boats in use was nearly 18 million in 2006, a figure that is 13 percent higher than in 1989. In 2006, boating generated $39.5 billion in sales and services, an increase of 6 percent from 2005.

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Granted, many of those billions came from the sales of wind- and people-powered crafts (sailboats, canoes and kayaks), but powerboats account for more than 11 million of the boats in use today.

“In the last year alone, we’ve increased our replacement marine motor sales by 40 percent over the previous year,” explains a remanufacturer. “I think the climate has a lot to do with it. You’ll get a lot of people out there boating around Memorial Day, and a lot of them didn’t change their oil or winterize their boat, so they’re likely to have something go wrong. The better weather, the more people on the water, the more failures. Plus, the length of the season has an impact. If it’s nice all the way through Labor Day, business will be better.

The same expert also says the economy has a lot to do with business in this market too. “If a car breaks down, the owner is likely to decide it’s easier to get zero percent financing and go buy a new car. You don’t have that easy option with a boat. So there’s a lot more money involved if you want to get that new boat. When people don’t have that extra income to buy a new $20,000 boat, they’re more likely to put a $5,000-$6000 motor in the one they do have.”

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Marine engines are a different breed of motor from the standard passenger car or light truck, despite beign built on Chevy 4.3L, 350 of 454, Ford 302 and 351 or Chrysler Hemi engines, as well as Isuzu, Cummins or Yanmar light duty engines, according to those who build them. Marine engines work a lot harder than automotive engines, experiencing much higher loads.

The typical marine engine in a pleasure boat might spend 10 percent of its time idling, maybe 60 percent of its running time at cruising speed (4,000 rpm), and maybe 10 to 30 percent of its time running at wide open throttle (5,500 to 6,500 rpm). A performance boat might spend 5 percent of its time idling, and 95 percent of its running time at wide open throttle at speeds as high as 8,000 rpm.

Stern drives typically have 1:1 gear ratios, so the engine has to pull much harder compared to an automotive engine that has gear reduction in the transmission, and addition gear reduction in the differential.

Because of these loads, marine engines don’t last like automotive engines.

The operating environment for marine engines is also entirely different. The engine is in a boat, which means it usually relies on the surrounding water for coolant.

Consequently, there are no corrosion inhibitors in the coolant and cooling system corrosion is a major issue. All the fittings have to be stainless steel, brass or some other corrosion-resistant material. With an offshore boat, the situation is even worse because the coolant is salt water. The highly corrosive nature of salt water means the cooling jackets inside the cylinder block and heads must be painted or coated to prevent the salt from eating away the metal.

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These adverse conditions mean there’s really no core exchange program with a marine engine, especially if that motor is run in salt water.

According to the NMMA, the life of the average marine motor is directly related to the maintenance it receives. The average marine gasoline engine will run for 1,500 hours before needing a major overhaul. The average marine diesel engine will run for more than three times that long and log an average 5,000 hours under the same conditions.

“The typical gasoline marine engine will run fine for the first 1,000 hours. It is at this juncture that the engine starts to exhibit small problems. If these small problems aren’t addressed, they can turn into major problems, which may make the last 500 hours of life difficult to reach,” explains the association.

“Diesel engines are built to finer tolerances than are gasoline engines. They will accept much more abuse and often deliver, if well maintained, 8,000 hours of hard work before needing a major overhaul.”

Although diesel engines are much more expensive in the marine industry, they are becoming increasingly more popular. One of the reasons is safety. Because of diesel fuel’s higher flash point than gasoline it does not present the same threat of explosion that gasoline fumes carry. Reliability and safety go hand in hand with a boat.

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A well-maintained gasoline engine run under the best conditions may well run for more than the 1,500 hours without major overhaul. And since the typical recreation boater uses his craft about 200 hours per year, these engines will seem to last forever. But, as with car owners, boat owners may not maintain their vessels as they should.

Cooling is a major issue with marine engines, even stock ones. Inboard engines are typically located low in the hull where there is little if any airflow around the motor itself.

The NMMA offers these recommendations: engine compartments should be supplied with lots of dry, cool (50 degrees F), clean air. The very minimum fresh air vent area (in square inches) for natural ventilation without blowers is found by dividing engine horsepower by 3.3.

Two of the most important rules of thumb for engine compartment blowers on gasoline engines are that they should always be set to exhaust, not to blow air in, and they should be run for a minimum of 5 minutes before starting the engine.

Fresh water engines often run quite cool (120° to 145° F), which can cause the rings and valves to gum up. An engine operating temperature of 160° to 180° F is better because it allows the engine to develop more power and experience less blowby (and less cylinder wear). But with salt water engines, going over 150° to 160° F may cause the salt to precipitate out of solution and form scum deposits inside the engine.

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Marine engines typically use water-cooled exhaust manifolds to preheat the incoming water, and to keep the manifolds from getting so hot they create a potential fire hazard inside the boat. But the exhaust manifolds are also very vulnerable to internal corrosion. If the cooling inlets, cooling system and exhaust outlets are not cleaned and maintained regularly, they can clog with corrosion and debris causing the engine to run hot, overheat and suffer damage such as scuffed pistons, valve sticking or head gasket failure.

The wet nature of the marine environment also precludes the use of a lot of electronics on the engines. Though many engines are now running fuel injection, the engine control module runs in open loop because no oxygen sensors are used in the exhaust manifolds. Some high performance engines do run digital pyrometers in the exhaust to keep an eye on exhaust temperatures so they can avoid running too hot and too lean (which may be too bad for the engine!). But most of the tuning that’s done is done in the shop on a dyno, and once the engine goes out the door there’s little if any adjustment that’s possible.
If you’re getting inquiries from your automotive customers about your abilities to service their boats, you may find they’ve noticed something amiss — and it’s usually in the form of exhaust gases. Here are some association guidelines of how to identify potential problems with boats based on their exhaust smoke.

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Exhaust gases from marine engines should be clear. Any color of smoke can warn you of potential trouble.

  • Black smoke is the result of engine overload, a restricted air supply, or a malfunctioning fuel injector in the case of a diesel engine. Improperly burned particles of excess fuel are blown out the exhaust.

  • Blue smoke is formed by combustion of the engine’s own lubricating oil. This can be the result of worn piston rings, valve guides, or oil seals. The oil can come from an overfilled air filter in the case of a diesel engine or excess oil in the crankcase.

  • White smoke indicates either water vapor from dirty fuel, a water leak into the cylinder or atomized, but completely unburned, fuel. Air in the fuel can also cause white smoke.

In addition to the smoke, boaters should check the level and condition of their engine oil regularly – at least once a day and preferably before every start, suggests the NMMA. Feeling the oil for its condition as they would with an automotive engine can alert them to foreign particles that could mean contamination or parts failure.

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In addtion to condition, the level of oil is crucial…but unlike your automotive customers, boaters may find that their oil level actually increases. Too high a level might be a clue that water has found its way into the oil sump. This could crack the cylinder head, break a piston, or both, just by turning the engine over. This mixture of oil and water will also look “milky.”

Too low a level could indicate an oil leak that could lead to engine seizure. Look in the bilge to see if there is any oil residue. Many marine engines sit very low in the bilge and water is consistently in contact with the oil pan. Over the years this can corrode and cause pinhole leaks in the pan.

Keeping up with the Davey Joneses

To the outsider, boating is often considered a luxury, but the NMMA says the average boater is actually middle class. Three-fourths of current boat owners have household incomes under $100,000, so it’s not as if getting into this market will introduce you to millionaires. Still, the Pandora’s box of “want vs. need” is just as strong in the water as it is on the street.

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“Look at it from the automotive side. I’ve got a ’68 Bronco with a straight 6 in it. I’m putting in a 351 Windsor that’s stroked out to be a 408. So I’m going to get a whole bunch of horsepower and a bunch more torque.” explains one source. Translate that to a boat: putting in a performance engine with more horsepower and more torque doesn’t correlate to faster on the water like it does on the street. If you go from something that’s 260 hp (about what you see from the standard 350) to 350-400 hp, you’re really not going to gain 20 mph on the water – it’ll likely be 5-10 mph.”

Still, a lot of it is a self-esteem thing, much as it is in the automotive world as well. If your neighbor has a ’66 Mustang, you want to have one that roars a little bit louder. That’s really what drives a lot of the marine market as well.

Selling crate motors that are better than OE for less to national distributors has been our niche…and we can’t make enough of them,” explains a remanufacturer. “I’d sell a luxury product over a commodity item every day.”

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