Flagship Marine
Keel Coolers
Keel Cool Diagram
Due to unparalleled quality and superior service backed by decades of experience, we have chosen R.W. Fernstrum & Company to cool our equipment and are happy to pass along our OEM buying power for not only dissipating your HVAC heat load, but also your power plant and generator equipment.

Rather than pump corrosive raw water through your equipment for cooling, install a keel cooler - you will extend your components life and never again have to clean a plugged strainer!
Ideal for shallow coastal waters where seaweed, algae, mud, sand and silt are a constant problem.
Fernstrum & Company
These coolers can be surface mounted,recessed or side mounted and have very little drag when properly installed.
Call us with your particular cooling needs and we will be happy to provide you with a very competitive quote.


You can eliminate your troublesome water pump completely if you use a dry exhaust system,and actually have no raw water in your vessel at all!

In most cases the engine's fresh water circulating pump is more than adequate for circulating water through the keel cooler by itself.

Surface mounting on an existing hull with a wedge shaped fairing block as shown will not only protect the cooler from striking an object, but reduce the drag to an almost non existent level.

  Surface Mounted Keel Cooler
Recessed mounted coolers offer the best protection, especially when hauling your vessel, and in new construction this is the preferred installation.
Recessed mounted keel coolers

 For a shallow draft vessel, you may mount the cooler on either the side or stern of the vessel in a recessed or surface mounted installation. For HVAC cooling that is used dockside only, we actually mounted a cooler on the transom!

  Shallow draft vessel keel cooler
 Side mount shown in a recessed compartment.

  Side mounted keel cooler

A BOX COOLER is one of our coolers mounted in a sea chest as shown. This offers you the best protection possible and gives you more flexibility for servicing and stacking multiple units in one compartment.

Variety of Keel Coolers

Many different types of connections can be custom designed to exactly suit your requirements - sketch our what you need and our design team will prepare a plan for your consideration.

 The unique Fernstrum design results in a smaller, more compact cooler for the same amount of heat rejection. The unique rectangular shape of our tubes provide a far greater surface area and negates the need for grooving, and our use of heavy gauge 90/10 CuNi we believe ends up in a far superior product.

So what does that do to the size of a cooler? In many circumstances, a kit cooler can be anywhere from 33% to 100%larger than a GRIDCOOLER based on the same cooling requirements. In addition, the sizing difference includes standard cooler loadings of 90% for a kit cooler and 75% for a GRID COOLER.

 Fact & Fiction
About Keel Coolers, in Particular the R.W. Fernstrum GRIDCOOLER

FICTION: A GRIDCOOLER can't be used in high speed applications.

FACT: GRIDCOOLERSare currently being used on high speed crew and patrol craft.The GRIDCOOLER creates a negligible amount of drag in high speed applications, and their sturdy design will hold up under the most demanding conditions.

FICTION: A GRIDCOOLER must be mounted in a recess.

FACT: Any GRIDCOOLER may be mounted in a recess or just externally mounted on the side, bottom or rake of the hull, depending on the vessel design.

FICTION: GRIDCOOLERS require too many through hull fittings.

FACT: Any GRIDCOOLER can use our L-Series option which requires only two through hull fittings, one for the inlet nozzle and one for the outlet nozzle.

FICTION: The GRIDCOOLER is more difficult to plumb than our competitors' coolers.

FACT: The two-pass or U-Flow GRIDCOOLER has both inlet and outlet nozzles on the same end of the unit. The nozzles can use a variety of fasteners including hose connectors, flanges, or threaded pipe.

FICTION: Grooved round tubing is more efficient than smooth rectangular tubing.

FACT: This statement might be true, depending on the cross-sectional area and perimeter of the two tubes used in the comparison, but don't be misled into believing that the grooved tubing used by our competitors is more efficient than our tubing. Efficiency of the cooling units in question can be determined by simply comparing the size of one unit to the size of the other. If a GRIDCOOLER and a grooved tube cooler are sized for the same application, our GRIDCOOLER will be the smaller unit.

FICTION: 70/30 copper/nickel is more durable than 90/10 copper/nickel.

FACT: If you are comparing apples to apples, 70/30 is only slightly more durable than 90/10 copper/nickel. However, in comparing our 90/10 to our competitors' 70/30, you may be comparing apples and oranges. Our 90/10 tubing is twice as thick as our competitors' 70/30. This increase in wall thickness more than makes up for any differences in material.

FICTION: Welded and brazed joints can crack and leak.

FACT: Unlike"O" ring slip joints which leak under vibration, welded and brazed joints will not crack and leak under normal operation, and many units damaged by severe groundings or being struck by debris will still operate effectively without leaks. In a heavy pounding sea, kit coolers and their gasket joints can easily fail.GRIDCOOLERS are built to withstand heavy seas.

FICTION: Brazed coolers can't be bent to conform to a hull's curvature.

FACT: Because of the ductile qualities of 90/10 copper/nickel and the inherent strength of brazed and welded joints, a GRIDCOOLER can be bent to meet your desired specifications.

Engineered Keel Cooling

QUALITY - Our 100% parts inspection process and rigorous testing procedures insure that all raw material and every GRIDCOOLER is built with the same exacting standards that prompted the U.S. Navy to set their keel cooling standards by the Fernstrum GRIDCOOLER. Nearly 25% of the production time for every GRIDCOOLER is spent in inspection and testing,from raw material to finished product. This level of quality control insures the dependability and performance that has kept our GRIDCOOLERSin service for as long as 30 years.

MATERIALS - A standard series GRIDCOOLER is made of either heavy gauge 90/10 copper-nickel or 5000 series marine grade aluminum rectangular tubing. These alloys were chosen because of their resistance to salt water corrosion and their heat transfer abilities. The copper/nickel units are silver brazed, and the aluminum units are welded. These construction materials and methods provide a level of durability far above any kit cooler.

DURABILITY - While 70/30 copper/nickel is marginally more corrosion resistant than 90/10,its lower heat rejection abilities make it a relatively poor heat conductor when compared to 90/10. However, don't be fooled into believing a kit cooler is more corrosion resistant than a GRIDCOOLER.A kit cooler uses a very thin walled tube while our GRIDCOOLER uses a much thicker wall tube. This thicker wall tube, and our welded and brazed joints, led the U.S. Navy to give the Fernstrum GRIDCOOLER a 20 year rating.

CONSTRUCTION - Kit coolers use "O" rings and gaskets to hold their coolers together for a "tight" seal. Unlike a kit cooler, the welded and brazed construction of a GRIDCOOLER provides a solid cooler.Welded and brazed joint construction also eliminates the excess wear between vibrating tubes and fasteners that occurs with kit coolers. Sure, you can replace kit tubes a bit easier, but why should you have to replace tubes?

PRECISION - Every GRIDCOOLERis built out of high quality pipe and sheet stock, not cheap out-of-round and thread bare castings or plug-and-pray seals. This allows us to let you decide how your GRIDCOOLER will attach to your vessel;and have peace of mind in knowing it will attach properly.

SIZE - The GRIDCOOLER is the most efficient keel cooler available. Our 90/10 copper/nickel has 1/3 more heat rejection ability than the 70/30 copper/nickel used by the competition. Our rectangular tube is much more efficient than the thin spiral round tube used by the competition. The size of our cooler can be easily compared to any of theirs. Based on the same information, our GRIDCOOLER can be as little as half the size of their bulky kit coolers.

PRESSURE DROP - Overheating,uneven engine cooling and air pockets in the cooling system are just a few of the problems associated with excessive pressure drop in an engine cooling system. Any one of these problems will cause premature engine wear and engine failure if the problem is not addressed. It also limits the types of pumps than can be used for coolant flow. Unlike the kit coolers you may see, our GRIDCOOLER is designed to create a minimum amount of pressure drop. Kit coolers using spiral tube create turbulence and turbulence is pressure drop. Kit coolers with only one through hull fitting severely restrict water flow, which creates pressure drop.

DESIGN FLEXIBILITY - With over 8000 GRIDCOOLER models available, we can recommend a cooling system that meets the unique needs of your engine on your vessel in your operating environment. Our standard GRIDCOOLER models can use any one of our five tube types, they can have between 4 and 24 tubes and they can be between 21 and 187 inches long(in six inch increments). If the standard configuration of a GRIDCOOLER creates a problem, we can make modifications as needed.

SAFETY FACTOR - Unlike kit coolers, our units have a 75% heat rejection loading, giving a built in safety factor of 25% for pump and impeller wear, internal and external fouling, re-powering, etc.

EASY INSTALLATION - Designed to be externally mounted or flush mounted on the hull, the GRIDCOOLER presents no greater problem than ordinary through-hull fittings.The GRIDCOOLER is a completely assembled unit ready for installation,complete with heavy neoprene gaskets for sealing the inside and outside of the hull. If needed, a GRIDCOOLER can be bent to conform to the hull's curvature.

SUPPORT - With over 50 years experience in the marine engine cooling market, we will engineer a GRIDCOOLER to meet your specific application and needs.We can give you advice on cooler placement, installation and service.Should you require an emergency replacement unit, we can have it shipped to you within three business days or less.

VARIETY - Kit coolers might be available in as many as a couple hundred models...GRIDCOOLERS are available in over 8000 standard models, and a near limitless number of specials can be built for your individual application.

NEGLIGIBLE DRAG - At up to twice the size, kit coolers create more drag than our GRIDCOOLER.After a combination of independent testing by the Vienna Model Test Basin and in-house testing was completed, it was proven that the Fernstrum GRIDCOOLER creates less drag than the difference in drag between spraying and rolling a coat of anti-foulant paint on a hull.

DAMAGE - If a kit cooler is damaged, a catastrophic loss of coolant usually follows due to the loss of tubes. Our GRIDCOOLER does not suffer from this problem. Because we use brazed and welded joints, the cooler may leak, but any coolant loss should be replaced.

Questions? Our Customer Service & Tech Support Team is Here to Help
800-316-6426 | sales@flagshipmarine.com

Flagship Marine Units NEVER Have Condenser Failures!
    The heart of every marine air conditioner is the condenser—the heat sink to the ocean and the only component the corrosive sea water touches is the inside of the inside tube.  Failure of this tube is catastrophic for the entire system. Even extremely corrosive places like the very high salinity of the Red Sea are no problem for Flagship Marine condensers because we use an unusually thick walled 90/10 CuNi (copper nickel) tube with particular annealment, hardness and other characteristics.
   We don’t dramatically shorten our condensers to save money by enhancing this tub: knurling or rifling for example. Our tube is “slick walled” with no thin spots that fester these failures.   
   Paper thin condenser tubes dissipate heat very quickly so the condenser tube can be short and inexpensive.  We don't cut corners by doing so.  We have full length condensers!  The shorter the condenser, the cheaper it is and the shorter it will last!
Our condenser wall thickness almost equals the shell wall thickness, ensuring decades of trouble free service.
   Flagship Marine has always prioritized durability and quality over cost savings and we NEVER cut corners. We also don’t skimp on our brazing material—ALL refrigerant lines are brazed with a 15% silver alloy, not the 5% typical of other manufacturers.
   As a result, Flagship Marine is very proud to have had almost ZERO condenser failures in the last two decades.

Every 5-7 years or so, it's good form to chemically clean the inside of the condenser tube with a phosphoric acid solution (such as "Barnacle Buster"), and if in fresh water every couple years with a bleach solution. In locations with muscle crab infestations more frequent treatments may be necessary. This will bring the condenser back to a like-new condition.

Over the years the heat transfer will be diminished by a marine growth which will gradually increase the refrigerant pressure and reduce efficiency. Simply circulate the solution through the condenser for a couple hours or so (depending on the dilution), and when you're done a high pressure garden hose will help blast away any stubborn deposits. Muriatic acid will also work but it unnecessarily removes the protective patina and is VERY hard on your lungs and the environment!

Hand Crafted in Stuart Florida
All Flagship Marine condensers are hand-crafted from start to finish at our Stuart factory location to our exacting specifications

Still Built with Pride in the USA
with Only Domestic Alloys.
No Cheap Imports.

Flagship Marine's chillers are the most rugged, commercial/military quality chilled water systems available! When downtime can equal lost dollars, the durable and dependable Flagship Marine units are money in the bank.
To make the very best in chillers we put the very best materials in the hands of skilled technicians. Our chillers are built to last decades. Made in the USA Since 1995
All stainless components are 316 marine grade stainless steel!
Evaporator housings, drain pans, electrical boxes etc.
are 5005 marine grade aluminum!

Copper Nickel socolets
Flagship Marine takes no shortcuts
with quality and design!

   All condenser tube to manifold connections are made with precision machined 90/10 CuNi (Copper Nickel) socolets that are TIG welded to the schedule 80 90/10 CuNi nipple with a monel alloy and brazed to the condenser tubes to ensure many years of trouble free service.

   This configuration meets all MilSpec and ABYC requirements. Naked connections aren't nearly as durable and fail to meet those standards.
   For your convenience all manifolds are fitted with reducing couplers and a 3/4" drain plugs for winterizing.

Welded elements
Welded elements

Expansion Valve

All Flagship Marine equipment incorporates expansion valves which adjust the modulation of the refrigerant to match the conditions of sea water, humidity and ambient temperature. This maximizes performance by preventing excessive or inadequate refrigerant head pressures, resulting in more cooling and extended component life!
This is why all new HVAC equipment must now use expansion valves instead of the capillary tubes you may still have in your home air conditioner.
We don't "cut corners" - these cost us about $75-175 each vs a $3.00 cap tube, and on the larger units we use "balanced port" rather than the standard expansion valves which automatically adjust to the amount of refrigerant flowing rather than being a fixed flow and out of balance.

Capillary tubes cannot adjust the refrigerant modulation which is fixed by the physical length of the tube. Like a broken clock that is right only twice a day, capillary tubes either over-modulate or under-modulate the refrigerant as the sea water temperatures vary. As an extreme example, if you are in upper Mississippi when the water is 40° and the air is 95° the modulation will be excessive and the head pressure much too low. Expansion valves adjust the modulation according to the conditions.
No Capillary Tubes

Dry Drain Pan
Flagship Marine Exclusive: Dry Drain Pan
No more mold and mildew starting in your drain pan!
We now manufacture sloped aluminum drain pans that are dry so the condensate water doesn't have a chance to grow mold and mildew.
sheet metal components
All sheet metal components are laser cut with aircraft/military quality tolerances in the ten-thousandths of an inch range as depicted here with the skeleton of an air-cooled chiller. Note the PEM nut inserts and numerous stainless steel rivets that result in a very rigid, strong and exacting structure.
Variable Frequency Drives
If your vessel is wired single phase or you have marginally sized generators, or if you want to almost completely eliminate voltage fluctuation when compressors start, we can install Variable Frequency Drives (VFDs) in our equipment. 
The VFD reduces the start up inrush and will greatly reduce any brown out, generator lag or flickering in your TV when the compressors start. 
The typical inrush (millisecond start up amperage) is about 5-7 times the running amps, however with a VFD the compressor frequency slowly ramps up to the 60 HZ speed so the inrush is typically about 1.3 times the running amps.  You can also manually program in lower or higher frequencies as well to accomplish running on lower amps or more output at higher amps if you need to, but of course you will lose or gain proportional performance by doing so.
Flagship Marine strives to provide the most simple, trouble free and durable equipment available, and frequency drives are not in keeping with the KISS principal that guides our component selection and design, however there are applications that warrant these excellent products.

Diagnostic Monitor with ICM Modules
Flagship's Exclusive Diagnostic Monitors Use
Time Tested "Over the Counter" ICM Modules
No Printed Circuits
With Flagship there are no expensive proprietary printed circuit boards.
No highly trained technician needed, typically a voltmeter and a
screwdriver is all that is needed to make most repairs!
All Flagship Chillers have a low voltage control module with clearly labeled LEDs advising the end user specifically what has tripped the chiller, be it high or low refrigerant pressure, freeze control protection as well as low chilled water flow. Diagnostic Monitor Panle

Programable Digital Control

Our new digital control is programmable or you can override the programs and manually control the temperature.

In addition to a host of features it has a back-lit screen for programming even in the dark.

ANY four wire battery-operated control will operate ANY Flagship Marine Unit

Personalize Your Thermostat

We will laser etch your vessel name here
for only $35.00

Personalize Your Thermostat
Questions? Our Customer Service & Tech Support Team is Here to Help
800-316-6426 | sales@flagshipmarine.com

Flagship Marine, Inc., 2427 SE Dixie Hwy., Stuart, Florida 34996 - USA
Phone: 772-283-1609 Fax: 772-283-4611 Wats: 800-316-6426 sales@flagshipmarine.com

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