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Marine Refrigeration

The beer is warm. The spinach is unfrozen. The ice cream is soupy. Refrigerators, whether at home or at sea, seldom fail. But when their time has come, it's time to go.

We fell into the marine refrigeration market when we decided to dump the 20-year-old Norcold on our 42' trawler. Over the years, it chilled beer nicely, while occasionally freezing things that shouldn't be frozen.

Recently, however, two things really began to bother the crew. The compressor seemed to run constantly, a sign that it finally might be aging. This was particularly an irritant at night, when sharp ears would lie awake listening to the Norcold chugging away nonstop in the galley.

But what bugged us most was the large freezer box/ice tray compartment that occupied nearly a quarter of the interior. For us, it was a total waste of space.

Our boat's first owner thoughtfully installed an ice maker and a freezer, so the two little ice cube trays in the Norcold were of little use. Why he installed the Norcold with its unneeded freezing space at first was a puzzle. The answer would become obvious: somebody had been on a budget and there was little other choice.

Because of that freezer compartment, the Norcold didn't have space for food and beverages for even a long weekend, so we carried an ice chest in the cockpit for soft drinks, fruit, and vegetables.

Some spacious trawlers can accommodate a refrigerator the size of one at home, or a slimmed down apartment-sized box. Most of us make do with the under-counter-type, which require stooping or deep-knee bending a dozen times while preparing a meal.

There probably still are a few older powerboats that have cavernous boxes into which big blocks of ice are deposited every now and then. For them, there are many systems on the market that make it relatively simple to convert to refrigeration.

Newer fridges are superior, thanks greatly to better insulation and more efficient electric motors. Although many off-the-shelf products are insulated with urethane foam, custom builders can buy insulating vacuum panels that are many times more efficient than foam, but much more costly.

If an off-the-shelf unit doesn't look right, it's possible to have a refrigerator custom-made to fit the available space, and to provide the features boaters want.

Norcold and other builders of 12-volt direct current (VDC) slip-in models obviously include a small freezer compartment in their refrigerators because that is what the recreational vehicle market demands. The huge RV segment of the market drives the design and marketing decisions, and the combo is the result.

The Thetford Co., a manufacturer of marine products, purchased Norcold last year. Maybe boaters will rank higher with Norcold in the future.

Some History

The basic principle of refrigeration hasn't changed in the one hundred-plus years since Clarence Birdseye (there were others, but those of us who shop the frozen food sections of our corner grocery recognize that name) figured it out and put it to work. The systems are better today, however, because motors and compressors are more efficient and electronic controls manage the process more effectively.

The technology of delivering cold hasn't changed much in 50 years, either. "It is all technology from the 1940s and 1950s," said Mike Bowden, owner of Ocean Options, a dealer with shops in Fairhaven, MA, and Annapolis, MD. "The only change has been in new refrigerants."

There is a new way to keep things cool, but it may be too new for marine consideration. It is called thermoelectric, and is a space age thing and slippery mentally.

Thermoelectric is based on the Peltier effect. When a low-voltage DC current passes through a junction of two kinds of metal joined in two places, heat is absorbed at the cold junction and dissipated at the hot. Got that?

Stick the cold junction part inside a box and you have a refrigerator with no moving parts, except for a fan. The six-pack coolers that plug into a cigarette lighter all use the thermoelectric process; larger units that might work on a boat are just now being introduced.

Askeland, Inc., of Cranston, RI, offers its thermoelectric Coolerator 2002 for $669 for boxes up to 12 cubic feet in volume. The price does not include the box, however.

President Leif Askeland said the water-cooled Coolerator 2002 draws 9.5 amps of 12VDC when operating in a fast cool mode, and 3.2 amps on its economy setting. It is designed for owner installation, by attaching it to the inside of a refrigerator box and linking up cooling hoses.

Askeland also makes a Coolerator 1001 for use in converting old ice boxes into refrigerators. It will cool up to 4.5 cubic feet to about 40 degrees below the temperature outside the box. Its price is $199.

Basic Theory

Keeping beer cold the old-fashioned way depends on one scientific fact: as a liquid evaporates into a gas, the gas absorbs heat from its surroundings.

A refrigerator is a closed system, within which is some kind of liquid refrigerant. For years, the refrigerant commonly used was ammonia or sulfur dioxide, both evil chemicals. Later, scientists produced a class of molecules unknown to nature and called them chlorofluorocarbons (CFCs), and thought they were environmentally safe. The best known of the CFCs is Freon, a DuPont product. We now know that CFCs are evil, ozone-damaging chemicals, so today we use a benign product called R134a.

While it still is possible to refill an old refrigerator with recycled Freon, the greenies among us will choose instead to buy something new filled with R134a.

Here's what happens inside the hidden recesses of a refrigerator: Under pressure, the liquid refrigerant is allowed to escape through a special valve and, evaporating, it comes out as a cool gas at low pressure. In a refrigerator, this gas flows through copper tubing (often hidden or enclosed in a thin sheet of metal called an evaporator plate) picking up heat as it moves along. (The heat gets into the refrigerator because everyone in the house is always opening the door in search of a can of pop, an apple or a scoop of ice cream. A refrigerator is surrounded by the heat of a house or a boat and, despite good insulation, that warmth penetrates into the area that is supposed to stay cold.)

Exiting the refrigerator, the gas, now warm, flows into a condenser that cools the gas, which then liquefies. And we're back at the beginning of the cycle, with the pressurized liquid escaping through the expansion valve.

Around and around it goes. The average refrigerator probably operates 40% to 60% of the time to keep food cool. They are wonderfully reliable, often running for decades without stopping. (The freezer in my garage was used when we bought it, at least 20 years ago. We have not spent a cent on repairs. Similarly, the Norcold on our boat has defied its reputation as a short-lived product and performed well for two decades.)

Evaporate Or Holding Plate?

There are two variations on this basic method of keeping food and drink cold. One, already mentioned, is the evaporative plate system. The other is the holding plate (or, some say, the energy accumulator) system.

The market offers many evaporative refrigeration systems. They operate just like the refrigerator at home. An evaporative system will run frequently to keep the refrigerator chilled. It switches on and off as demand requires.

The Norcold is a classic example of an evaporative system refrigerator, ready to install under the counter.

A much more costly choice is cold plate refrigeration. The plate is a box, two to four inches thick, sized to fit inside the refrigerator, across the side or top. The plate is filled with a fluid (alcohol, antifreeze or calcium chloride compounds), in a network of tubes that carries the refrigerant.

As the compressor works, the fluid freezes. It then holds its chilly temperature for many hours without further effort by the compressor. A holding plate does a good job of maintaining the 40 degrees required in a refrigerator without turning the compressor back on for at least 12 hours. Some super units last even longer.

Major builders of marine refrigeration components and systems offer both evaporative and cold plate units. These companies include Grunert, Adler/Barbour-Crosby, Glacier Bay, Sea Frost, Frigomatic, Technautics and others, including local shops that build custom systems with off-the-shelf components.

The problem with holding plate systems is that they are enormously expensive, costing three to four times more than evaporative systems. Or more.

The only real advantage of a cold plate system is that the owner chooses when a holding plate compressor is to operate; he or she has no control over when an evaporative refrigerator turns on or off.

When holding plates were first introduced to boaters, they were a blessing for sailors, whose boats had insufficient battery capacity to run a refrigerator, and whose feeble engine alternators would have trouble keeping one charged. A sailboat owner would only have to run his engine twice a day to drive the compressor just long enough to freeze the holding plate.

Today, with the availability of deep cycle batteries and high-capacity engine alternators, holding plate refrigerators offer no benefits to powerboaters and few advantages to sail boaters-except, perhaps, for circumnavigators and others on long ocean crossings. A powerboat making an ocean crossing certainly has the ability to handle the frequent energy demand of an evaporative plate refrigerator.

An evaporator plate draws a little power fairly often. A holding plate system hits the energy supply hard twice a day for a prolonged period. Both kinds work well.

There is no good reason for powerboat owners to install a holding plate refrigerator or freezer. They are no better at cooling than an evaporator refrigerator, and are ridiculously expensive. Holding plate refrigeration was developed decades ago to keep ice cream delivery trucks cold.

In the 1970s, small holding plate systems were introduced to the boating market by Grunert and Crosby, giving sailors reliable mechanical refrigeration for the first time.

Many of today's sailors, who make the switch to power from sail, order a holding plate system for their new trawler because it is what they know best, said Mike Bowden of Ocean Options.

These ex-sailors like custom boxes, with fine woodwork and stainless steel fittings, and controls that will manage temperatures closely.

Typically, he said, a custom holding plate installation will cost $3,000 to $8,000. Bowden installs them on large yachts. He also sells Norcold refrigerators to budget-minded boaters.

Despite the extreme differences in cost, some powerboaters still prefer holding plate systems.

Chris Washburn, owner of Washburn's Boat Yard in Solomons, MD, installed a holding plate in the refrigerator of his 42' Krogen.

"In the case of my Krogen, while cruising to Nova Scotia we would run the genset half an hour in the morning. And that was it. The cold plate would get cold and stay cold," Washburn told me. "When we went to the tropics, we would run it 45 minutes in the morning, and half an hour at night."

For the long-distance cruiser, who may want to spend days at anchor in some hidden cove, the holding plate should be considered because it minimizes recharge time, Washburn said. After two years of cruising, his Krogen had 2,000 hours on the main engine and 400 hours on the generator.

"For going from marina to marina, and on an occasional long cruise, it's better with an inverter and a standard (refrigeration) system," he said.

Although holding plates are costly, Washburn said the biggest cost is in building an insulated box. "People come in with a hole in the wall and it's a big expense to build the box to fit that hole."

The high price of a holding plate system will knock them out of consideration for most trawler applications. An evaporative system makes just as much cold for a lot less.

Noting the cost difference, one industry skeptic said: Take the money you'd spend on a holding plate and put in the bank. Use the interest to buy ice.

What's Available?

The choices available to a trawler owner shopping for a self-contained replacement 12VDC refrigerator, like the Norcold, are limited. Those who have a remotely-located refrigerator compressor have more options.

If an older trawler has a Norcold refrigerator it probably is a Model 704, which the company sold until 1991. That's the unit that's been keeping us awake on our boat. The refrigerator offered by Norcold as a replacement is Model 541.

The trouble is that the 541 is shorter, wider and deeper than the 704, and simply can't be fitted into many boats without extensive cabinet work. In some trawlers, there may be no way to make a 541 fit.

Norcold said it made the change to allow the front of its small refrigerators to be flush with the face of the cabinet. The older 704 sticks out beyond the cabinet front.

Norcold says parts are still available for the 704, so there's no need to toss one just because it quits.

There are a few 12VDC slide-in, under-thecounter refrigerators on the market that should fit the 704 space: Nova-Cool of Canada makes one precisely the same dimensions, while the Coolmatic by Waeco International of Germany is an inch or more smaller in each dimension, requiring new trim to cover the gap.

This kind of swap will cost between $800 and $1,000, assuming the owner does the installation, and doesn't need massive cabinetry work to make everything fit.

Because the cooling equipment is in a compartment within the box, it's usually simply a matter of unscrewing the refrigerator mounting brackets, disconnecting the power plugs and pulling it free. The entire unit weighs less than 100 pounds, so only one helper should be needed to slide the new one home.

So they're easy to install. But they also include ice cube makers, cutting into precious refrigerator space, which puts them at the bottom of my list, at least temporarily.

Something else to consider: Industry technicians tell me that Norcold builds its own refrigerator compressor. If any part fails the whole works must be replaced. Nova-Cool and Coolmatic use a Danfoss compressor made in Denmark or Germany, and whose individual parts may be replaced or repaired. The cooling fan on a Danfoss, for example, is a simple computer cooling fan, easily replaced.

Norcold is the Bayliner of marine refrigerators. It gets bad raps that are often undeserved. One is that the Norcold compressor has a short life, maybe 10 years. Ours is 20 years old and, despite its idiosyncrasies, still works.

If a trawler owner is pursuing a new refrigerator simply to get a larger one, the simplest way may be to buy one of the free-standing portable boxes, about the size of a picnic cooler, that work either as a freezer or a refrigerator. They can be put any place within reach of 12VDC, under a table, in the cockpit, or on the bridge. If it goes outdoors, be sure it is weather resistant. Many are not.

Some boater-fishermen carry one or two of these portable units to chill or freeze their catch. You can buy them off the shelf in many stores; custom refrigeration shops also will build them for you.

What, Or Who, Is Danfoss?

I had been hearing about Dan Foss as I did my refrigeration research and began to wonder, who is this guy?

Turns out Danfoss is a large firm based in Nordbork, Denmark, with factories in many places, including China and Mexico. I found the company on the world wide web and learned that it is a leader in refrigeration and motor controls.

But still, what is a Danfoss? I dropped by Scan Marine on Seattle's Lake Union and talked with the owner, Karl Westerberg, whose business specializes in heating and refrigeration. On the shelf in his office was a shiny, black Danfoss. This is the compressor that chills refrigerator boxes in countless boats and RVs around the world.

The whole thing would fit in a big shoe box, or at least a bread box. (It's six inches high and 13 inches long and weighs about 13 pounds.) It will fit in a notch in a self-contained refrigerator (Nova Cool, Coolmatic), or it can be installed nearby as part of a custom installation, and connected to an evaporative plate in a refrigerator box.

On one side was a small domed structure, and on the other a radiator-like device with a small computer fan in front. Several copper tubes ran between them and others ended in mid-air, waiting to be connected to a refrigerator box.

This little machine will run on 12 or 24 VDC, drawing about 45 watts, or 3.75 amps at 12 volts. It will cool a refrigerator of up to 12 cubic feet of space, or a freezer of about five cubic feet. The newest Danfoss is the BD35F, which is advertised as being 20 percent more efficient than its predecessor.

The Danfoss is not designed to run full time, so sizing the refrigerator box correctly is important and worth calling on a professional like Westerberg.

Choices, Choices

If a trawler owner wants to pursue refrigeration options beyond all-in-one units like the Norcold, Nova-Cool and Coolmatic, the market choices widen significantly, and the cost shoots skyward. Among them:

Toss the old refrigerator box and build a new box with gobs of super insulation. Then buy a new 12VDC compressor and mount it in some nearby space and connect it to a new evaporator plate in that box.

This is the system many boats already have: an insulated box, a remotely-located compressor and an evaporator plate in the box. If you're tempted to replace the mechanicals and keep the old box, listen to this warning: experts say that if the unit is so old the compressor died, the seals and insulation around the box also may have failed. Check it out.

(It can be a challenge to find a place for the compressor. Visiting a Dutchbuilt motor yacht recently, I admired a custom holding plate refrigerator and freezer. The teak doors curved to match the bulkhead in which they were mounted. The compressor was across the galley, beneath the stove. Service or repair required removal of the range and an adjoining cabinet.)

A number of firms build refrigerator components that can be installed as remote modules, with quick-connect tubing and fixtures for owner installation. Among them: Grunert, Adler/Barbour Crosby, Sea Frost, Waeco, Glacier Bay, Technautics, Frigomatic. There also are custom shops along every waterfront with the skill to build any system a boater might need, using components from these and other manufacturers. Many are available in 120VAC as well as 12VDC.

While you ponder buying an evaporator plate system or a holding plate refrigerator, there are still other considerations: do we choose an air or water-cooled refrigerator? Does the compressor go in the engine room, lazarette, or under something? Do we build the box ourselves, or hire it out? Do we use the traditional urethane foam insulation? Or do we mortgage the boat and buy some of the new vacuum sheet insulation?

If your engine runs a great deal, consider an engine-driven compressor. But this adds complexity, in the form of shafts and seals that may leak, tubing running through the engine room, and the need to add a backup electrical system for those hours when the engine is off. It is very expensive, too.

David Lehmann of Sea Freeze in Bellingham, WA, a builder and installer of custom refrigerators, said an engine-driven refrigerator with an electrical backup "is a plumbing nightmare."

One could easily spend from $1,200 to $5,000 on such refrigeration alternatives-plus whatever it takes to build a new box, which could cost as much...or more. A lot of money to keep beer cold.

Another possibility is to keep the Norcold box, but rip out its compressor and evaporator plate. Buy a stand-alone compressor and plug it into a new evaporator plate installed in the old box. This is done, but to me that's rather like putting a Corvette engine in a 1975 Honda. You'll still have an old, poorly-insulated Norcold that will not perform particularly well, and may still have a tendency to run all night.

Why not just call Norcold and order a new compressor?

Here's another choice: If your boat has been updated with a 2,000 or 2,500-watt inverter, and deep cycle batteries, consider going to an appliance store in your local mall or a discount hardware store, and purchasing a 120VAC refrigerator built for household use.

"The commercial (household) stuff is cheaper, and it's more dependable," said Mike Bowden of Ocean Options.

A Norcold 704 or 541 has barely three cubic feet of refrigerator space, not counting the ice cube tray-freezer. One of the household alternatives, the 75R by U-Line (it is only a refrigerator- no freezer box!), has six cubic feet of space for food and beverages. The U-Line is about an inch taller and wider than the 704, and one should measure carefully before buying. In our boat, the hole for the 704 was cut comfortably large and the U-Line would fit with only some minor carpentry work.

Most of the major appliance makers, from Sears to Sub Zero, build under-the-counter and other, smaller refrigerators that will work well on a boat. I've seen them for as little as $300 for a cheap import. But expect to pay $700 to $800 for an AC box designed to go under the counter. You see them everywhere if you look: in coffee shops, delis, offices, recreation rooms, wherever there's a need to cool beverages and snacks.

The U-Line begins to look attractive by comparison. The company thinks about boaters, too. Its refrigerators and freezers may be equipped with locking pins so doors don't fly open in rough water.

Cruising The Tropics

Richard Kollman, of Fort Lauderdale, who has written about refrigeration for boats cruising the tropics, said one problem with using systems built for homes is that they are less energy efficient than 12VDC refrigerators like the Danfoss. Home systems have become more efficient in recent years, but they still have an unlimited amount of energy as long as they are plugged in.

Kollman also argues that inverters are less efficient than advertised when used to power inductive motors, as used in AC refrigerators.

And Kollman warns that too little attention is paid to insulating a marine refrigerator.

Insulation Is Critical

"The most important thing is insulation," he said. "R Values do work. If insulation is six to eight years old, it is probably no longer as good as today's insulation."

Most stock refrigerators have about four inches of urethane foam for insulation. Freezers should have about six inches of foam. (Freezers use refrigerator compressors, which just work harder and consume more energy as they drive the temperature to zero. In some systems, the same compressor will run a refrigerator and a freezer.)

Ron Sevier of Glacier Bay, Inc., a San Mateo, CA, manufacturer of refrigerator components, agrees with Kollman.

"The bottom line to all of this is that while everybody gets worked up with the kind of system to use, I tell you they need a good box first." Sevier recently ripped the old ice box from his sailboat and installed new refrigeration equipment and a new, well-insulated box. It was, he said, "a daunting task."

As he dug out the foam insulation from around the old ice box, Sevier found it was saturated with water, probably condensate. It was useless.

If installing just a new remote compressor, heed Sevier's message. Carefully check the insulation around your existing box for moisture or damage. If the insulation is poor, even a new system will have trouble keeping the box cold, and will consume far too much energy.

The newest insulation on the market is a vacuum panel, which uses the principle that keeps coffee hot in a Thermos bottle. It is usually custom made and very, very expensive-it may cost $1,000 to insulate one refrigerator. One splinter or exposed screw head can rip the panel and destroy its insulating qualities.

Glacier Bay manufactures a vacuum panel called Barrier 20; for a refrigerator, the panel is one-inch thick and has the insulating capacity of four inches of urethane foam.

Some boaters go to lumberyards and buy sheets of stiff blue foam made by Dow to supplement existing insulation. One inch has an R value of 5. It can be cut to fit and glued in place. Another builders' product is a similar foam board known as polyiso, which has an R 7.2 rating.

Cooling Considerations

Home systems are air-cooled. Those used on boats may be air- or water-cooled.

(Those cooled by water, pump a steady stream overboard, often prompting good-hearted, but unknowing neighbors in the marina to report that the bilge pump is running nonstop, suggesting that the boat is sinking.)

David Lehmann of Sea Freeze will build water-cooled refrigerators, but would not leave a boat for long periods with the water pump running, because they are subject to wear, leaks and the occasional blocked raw water intake.

Bob Tutwiler, a sales and customer service representative at Sea Frost, added: "Water cooling is the buzz word, some say it is more efficient. But it is a hassle with another DC motor, with brushes and through hulls. It's not worth it."

Energy Requirements

Next to a dedicated freezer, a refrigerator is the hungriest energy hog on a boat. Amps are important, and you should know how to count them and calculate the demand on batteries and generators.

A Norcold, Nova-Cool, Coolmatic and other self-contained 12VDC refrigerators draw between four and five amps of battery power. If it runs 12 out of 24 hours, it will use between 50 and 60 amp-hours of energy, although some say it may use as much as 80. An average 8D battery will carry that load easily for a day, as long as there are no other DC systems tapping into it.

When the trawler's energy load includes radios, stereos, water pumps, electric toilets, lights, let alone a freezer, the amp-hour load rises quickly and several batteries may be needed. But one of these 12VDC units shouldn't break the energy budget.

If you consider moving a household fridge onto a boat, you need to think about where to find AC power. Owners who run generators day and night have no worry...just plug in. But if an inverter is in the circuit, count your amps carefully.

There's a formula to calculate the draw on DC batteries whenever an inverter is used to feed 120VAC to an appliance such as a refrigerator. Multiply AC amps by 10 to convert to DC, and multiply that answer by 1.1 to compensate for the inefficiency of the inverter.

This is how the U-Line numbers work: Plugged into 120 VAC shorepower, the refrigerator compressor motor draws 2.4 amps. Multiplying by 10 gives us 24 DC amps. Multiplying again by 1.1 produces a total DC battery load of 26.4 amps. That's a fairly large hit on battery capacity, but is one that can be carried by a properly-sized bank of deep cycle batteries linked to a large inverter.

My selection criteria was this: could my batteries and inverter support a refrigerator and other DC loads, while at anchor from 3 PM today until 9 AM tomorrow, without recharging?

If the refrigerator runs one third of those 18 hours, 158.4 ampere hours would be sucked from the battery bank. Because it is recommended that only about half of a battery's capacity be tapped, at least two deep-cycle batteries would be needed to carry the refrigeration load. Add in other house energy demands (lights, TV, stereo, and a small freezer), and the number of batteries needed increases.

Our trawler has six-volt deep cycle batteries connected in series to produce 12 volts. They have a storage capacity of about 700 ampere hours, sufficient to carry the refrigerator, the small freezer and other minor AC loads over the test period. (The ice maker would be too much, so we operate it only while plugged in at a dock, and store the ice in the freezer.)

Yes, our electrical system would carry the load, assuming reliable batteries. I've found that pampered batteries, checked frequently, fed distilled water and recharged properly, will last many years. Add the cost of a set of replacement batteries to the price of a home-style refrigerator and the total still is less than buying a new compressor and evaporative plate to update an existing refrigerator.

How big should the battery system be? Glacier Bay, the California manufacturer of boat refrigerators, says: As big as you can afford and find space for.

A warning: even if battery supply is adequate, an inverter may not be able to handle the load, if several major AC appliances kick on at once. Your DC system may crash.

Energy management is important when the supply is limited. That includes watching what gets turned on, and controlling, as much as possible, systems that turn on automatically. Some owners with a refrigerator and freezer (either AC or DC) turn the freezer off overnight. If it had been chilled to zero degrees, and if it were not opened, everything should still be frozen hard in the morning.

Big engine alternators will recharge the batteries and pump up the freezer again while the boat is under way the next day.

What's All This Mean?

If a boat has all the good stuff-a big inverter, a bilge full of deep cycle batteries, hefty alternators, then a 120VAC refrigerator could make sense. If you have to purchase all of these items just for the sake of a refrigerator, it doesn't.

Thinking about all the available systems, it seems clear that those of us who like to keep things simple will vote for a 12VDC self-contained refrigerator. Yeah, something like the Norcold.

It would not have water cooling. It would not have a holding plate. It probably would have a little ice cube tray. Modest cost. Easy to install. Cheap to operate. Reliable.

Some of us want more-complex refrigeration, with a remote compressor that may operate a refrigerator and freezer. Unless the box is a total loss, with inadequate insulation, it's probably best to stick with what you have. Repair and replace as necessary.

It doesn't make sense to drop a couple thousand dollars on an inverter and deep cycle batteries, just to use a household refrigerator. If that gear is in place and already reliable, the little boxes from Sears, Sub Zero, Whirlpool, ULine and others look attractive. The shopper has greater choice and may find one that works better for boating than anything available in a marine store.

Refrigerators are everywhere, and so are repair people. I bet it would be easier to get a hometype refrigerator repaired in small and distant sea ports (look at all the Sears repair trucks on the streets) in the unlikely event one failed.

Whatever your choice, stay cool.