Frequently Asked Questions
Nigel Calder Changes his mind!
About Mexicolder Systems
Handy Hints to keeping your cool in the Tropics

Frequently Asked Questions:

Do I need water-cooling for the fridge and freezer?
No. For the amount of heat/hour the Mexicolder removes from the box, water-cooling is ABSOLUTELY unnecessary, In fact, with a water-cooled system, the energy to power the pump uses more precious amp hours.

We are concerned about the heat from the system warming the interior of the boat in the tropics.
The radiant heat from sunlight on the deck, cabin and hull far exceed the heat produced by the Mexicolder, in short you won’t notice the difference. Boiling a kettle of water for 2 cups of coffee or cooking creates much more heat than a Mexicolder.

I have seen keel cooled systems advertised that do not need a fan or a pump, will this work for me?
Yes, we built several prototypes that worked, BUT…….. Nothing comes for free and for this reason Mexicolder uses air cooling, When you are hauled out for underwater maintenance the keel cooling system did not work and when left on it damaged the compressor which is the heart of the system. Imagine being in a boatyard for even a few days and loosing those cold drinks and ice when you need them the most? Not to mention a freezer full of meat or seafood. In addition to the former you have to bore a 1 ½” hole though the hull and pay for the haul, launch and labor to do so. Even though keel coolers are made of bronze they are still susceptible to stray current corrosion. You don’t need to haul out to install a Mexicolder, or ever need worry about future corrosion issues.

There are other systems on the market that use cold plates and high capacity compressors, they cost many times more than a Mexicolder and then there is the install to pay for, so even if cost were not an issue, why wouldn’t I opt for one?
Cold plates are history, they are heavy, and they occupy the well-insulated box space you have supposedly created to store food in! They are problematic as most require expansion valves with mechanical connections that are prone to refrigerant gas leaks. Often they use a larger compressor and lots of associated and sophisticated control equipment to cool them so that means even more weight in batteries and heavy cables to supply the current. Add to this mélange the solenoid controlled valves, multiple wiring blocks, looms, suction accumulators and suction control valves………so much more to go wrong. Ask Nigel Calder.

What about engine driven systems?
In our opinion they are history too. From their first introduction and our personal experiences they were one of the most problematic systems we ever had or have worked on. In short, the operating pressure of the compressor at the end of the cycle is lower than the compressor was designed for in its role as an automotive air conditioning system. This often causes problems with the shaft seal and the system can get shut down due to moisture entering past the seal. The other disadvantage is that you are literally bound to your vessel, as the engine must be started at least once a day. Say goodbye to extended inland trips.

Do you offer “ high tech” digital controls?
No, the simple thermostat does a great job and is trouble free. If you insist, yes, we can custom install all the “bells and whistles” you desire, however we will put a switch in the system so that if you ever get hit by lightning, have a power surge or the digital control gets knocked out by your H.F. radio transmissions you have the option of having a simple, reliable thermostat.

Why is a high capacity compressor that I see advertised, advantageous?
It is not, as heat moves very slowly, and even more slowly as the temperature drops.

1.Think of your fridge box as the bilge and the fridge system as a bilge pump and the bilge water as heat.
2. If you had a lot of water leaks into the bilge you would want to stop them, this equates to building a well-insulated fridge box, thus stopping heat leaking into the box.
3. If you have a well-insulated fridge box, you have a smaller heat leak into the box and so you need a smaller more efficient pump (fridge system) to remove it at a regular interval.
4. Try sucking a cup of water out of the bilge with a 1 ½” hose size pump, then try with a ¼” hose size pump and you’ll understand.

We need both a fridge and a freezer; do we need to buy two units?
No, in almost all cases if the boxes are next or near to each other the cold air that spills over from the freezer box will keep you drinks ice cold and veggies fresh and crunchy. We built a custom system that use a small circulating fan and insulated 2” pipes to cool an auxiliary box when the boxes are split either side of the galley range like on the Catalina 42 “Ceilidh”, this works very well, the information can be found on this site.

Assuming we purchase and have you install a system, what happens if we need spare parts in New Zealand or somewhere else on our circumnavigation?

All the moving components in the system are available in any developed country anywhere in the world. The system was designed with this in mind, we have been there! We offer a cruisers spares package for less than $100.00 including tax, for those going further a field. The key to the energy efficiency of the system is engineered within the static internal design features.

Where did the Mexicolder system come from?
An ANSWER to SATISFY hundreds of sailors who, over the last 28 years worldwide asked us “why can’t I have a boat fridge system as reliable as a domestic fridge/freezer?”

Good QUESTION…why not?
We took a blank sheet of paper and years of hands on experience. Then we wrote down all that was good and all that was not good of all the systems available on the market in the mid 1990’s. We kept the good stuff and then tested and tested and tested aboard a cruising sailboat in the severe heat conditions during several summers in the Sea of Cortez Mexico. We then removed all the excess moving parts that were “fluff” but doubled up on the stuff that kept the compressor or “heart of the system” beating nicely. Then we chose the finest quality materials to build a simple, lightweight and efficient answer to the sailor’s needs and dreams.

Where can I have a Mexicolder installed?
At the time of writing, only in Mazatlan Mexico. There are independent contractors who can make box modifications, or all the materials available to do it your self.

Nigel Calder Changes his mind!

Excerpts from "Cold Comfort" Jan 2004 Sail Magazine:

"For a decade or more I have been an advocate of high-capacity DC holding plate refrigeration for cruising boats. I've recommended such systems to numerous people, have designed them or a number of boats, and have installed them on my own boats. But the technology has changed, and with it my cost/benefit analysis of different refrigeration options. Now I'm faced with having to ignore my own advice."

"...I believe the balance has shifted in favor of constant-cycling DC refrigeration, even on a hard-core cruising boat."

About Mexicolder Systems:

Our systems utilize the vapor /pressure system and a double air cooled condenser that keeps the high pressure down and thus the amp load too.

We can offer custom installation in Mazatlan. Dealers and installers in other ports are welcome to contact us.

Other systems on the market use user installable "Quick Connects" between the evaporator plate and the compressor. Over time the vibration, heat, and constant motion on a boat in the tropics take their toll on user installable "quick connect" fittings. These "Quick Connect" fittings begin to leak, which allows the compressor to suck in moist hot air, which destroys the compressor. We have replaced the "quick connects" for numerous cruisers in out of the way places, where there would normally not have been a refrigeration technician available. We believe that long term dependability and increased efficiency is dependent on having connections brazed instead of using leak prone “quick connects.

Mexicolder Compressor Considerations:

In all vapor compression refrigeration systems such as the Mexicolder Tropical Yacht Refrigeration System, we are "pumping" heat out of a hopefully well insulated box into the ambient environment.

1. It stands to reason that the compressor skid should be mounted in an area that is not heated up by an engine, generator, water heater, space heater or direct sunlight. The compressor skid needs to be in a dry area of the bilge, at cabin sole level where the dual fans can draw air from the cabin through the condenser and then cool the compressor housing and the electronic control module. Hot air raises so if the unit is fitted below a set of galley draws or berth, ventilation holes will need to be made to let the heat escape. Do not mount the compressor too near to the box you are trying to cool for obvious reasons!

2. Mexicolder Tropical Yacht Refrigeration Systems were designed to run efficiently on air cooling alone in temperatures up to 120 degrees Fahrenheit, rarely if ever does the bilge area of a vessel in the water near this extreme. The twin fan condenser ensures liquidity in the refrigeration cycle in the most extreme conditions. Tests in Mexico have proven that water cooling the system is not needed and this just increases the amp draw. Another important feature of air cooling is the elimination of stray current corrosion within the Mexicolder Tropical Yacht Refrigeration System and the need for another through hull fitting, pump and associated hardware, all prone to failure and at worst the cause of a sinking.

3 .The Compressor/Condenser skid should be wired directly to the batteries, not through the electrical panel or battery switches. This will ensure that the control module senses the true battery voltage. Although a 15 amp fuse is fitted on the compressor skid the American Boat and Yacht Council (A.B.Y.C.) recommend fitting a fuse at the batteries in the positive conductor. The removal of this fuse can also be used to depower the unit if so needed. From the skid to the batteries measure the distance in feet there and back to give ascertain the total wiring run in feet.

For wiring runs up to 12 feet use #10 AWG wire.
For wiring runs up to 20 feet use # 8 AWG wire.
For wiring runs up to 30 feet use #6 AWG wire.

The above specified wire runs are for 3% voltage drop. The wiring should not be bundled with other wires. Crimp on the end fittings and solder them too. Apply electrical tape or preferably heat shrink tubing. Connect the positive (red) wire to the positive terminal on the skid wiring block and to the positive battery post with an in line 15 amp fuse. Connect the negative (black) wire to the negative terminal on the skid wiring block and to the negative battery post.

Handy Hints to keeping your cool in the Tropics

from Mexicolder Tropical Yacht Refrigeration Systems

All of the following tips will help to reduce the "REFRIGERATIVE LOAD" on your fridge system, and thus reduce the amount of amp hours you burn. A refrigerator or freezer maintains items cold or frozen by removing heat from the box where the food and drinks are stored. Once everything is at the desired temperature, the "REFRIGERATIVE LOAD" is the heat leakage into the box from the surrounding ambient conditions, plus any warm stuff you put into the box.

For example: A six pack of beer in aluminum cans weighs 78 ounces, if in La Paz in July this beer purchased off a beer truck will be about 95 degrees Fahrenheit. Now..even being English I personally prefer beer at about 40 degrees. To calculate the amount of heat we need to remove to cool the beer to an acceptable temperature the following calculation is made.
Warm beer temperature minus cold beer temperature, multiply this by the weight of the beer and cans in pounds, then multiply this by the Specific Heat of Water = 1 ( we're talking about American beer)

The math is:
95-40 = 55 x (78/16) x 1= 268 (rounded) this is the amount of heat in BTUs (British Thermal Units…heck we invented it!) we need to remove from the beer. Consider a typical small 12 volt boat fridge system removes about 350 BTUs per hour and it is easy to see why they work so hard and burn up so much power. Now, suppose you are real smart cruisers and went ashore and bought already cold beer and put it in a cooler with some ice, now that's thinking, because even if /when the taxi breaks down and you show up with that same six pack at 55 degrees , you will only need to remove 73 BTUs of heat, to get the stuff back to 40 degrees. Other foodstuffs have different Specific Heats, all based on the water versus fiber and fat content. Fruits and vegetable are 80 to 90% water so their specific heat is 0.8 to 0.9. It is easy to see how having things pre cooled will lower the amp draw.

Another example, but with a twist in the tail…
To cool 10 lbs of freshly caught Dorado fish from a seawater temperature of 89 degrees to 20 degrees where it will be good for about three weeks the calculation is 89-20 = 69 x 10 .lbs x 0.7 (specific heat of low fat fish) = 483 btu's. Now for the twist, since there is less water in the fish than the beer, the thermal conductivity of the fish will be lower, so cut it into serving thickness filets rather than large chunks and lay it well spaced against the coldest part of the freezer plate to get it to freeze quickly.

Box Considerations:

1. Ideally there should be 5 to 6 inches of closed cell polyurethane foam on all sides of the box and on the bottom. Lids can get away with 3 inches. Check around the box casing, open the galley draws, perhaps you can squeeze a couple more inches here and there. Add as much foam as possible on engine room bulkheads. A reflective outer surface will help to reduce radiant heat leaking into the box. Closing curtains or hatches to stop the sun beating on the counter top will help no end.

2. There should be good seals on the lids and front openings are a no-no for energy efficient offshore cruisers, so seal them up with silicon and don't use them if there is a top entrance too. An easy way to improve the seal on the top is to lay a large place mat or rubber type sheeting on the counter top that can be rolled out of the way to open the box lids. This stops the moisture in humid air from reaching the evaporator and prematurely frosting it up.

3. Defrost regularly, ice on the plate is an insulator and stops the heat being efficiently removed from the box. NEVER use a sharp implement to remove ice. Transfer all food stuff to a cooler and switch off the compressor. Pour warm water on the plate and allow the ice build up to fall off. Thoroughly clean and dry the area and then after the plate is at ambient temperature switch the unit back on.

4. Extra unused box space should be filled with gallon or liter containers of fresh water, (or cases of sodas or beer) this acts as a temperature ballast. As produce and items are removed from the box replace the space with more water bottles or drinks or towels or cushions/pillows double wrapped in plastic bags. This means every time you open the box you don't suck in as much air at ambient temperature as you have reduced the actual amount of free air space inside.

5. Make sure the box drains are covered or fitted with a plug.

6. Hang a white piece of sheeting or canvas over the rail, immediately outboard of the box to reduce the radiant heat gain from the hull when the sun beats upon it. You might even have some insulating foam stitched between the two layers.

7. When you go to provision, tote a collapsible or solid cooler with you so that pre cooled meat, produce and drinks are put into the box cold.

8. A small low amp computer cooling fan mounted on top of a PVC tube can be used to circulate air in the box and maintain more even temperatures. On most Danfoss compressors the fan is connected in parallel with the condenser cooling fan, but be sure the total load of both fans does not exceed 0.5 amps at 12 volts, otherwise the black control box will be damaged. If the fans do exceed the rated load then a relay will need to be fitted. On Mexicolder units this relay is already fitted and so it is a simple job to piggy back spade connectors onto the fan terminals of the relay that sits on the double fan condenser shroud.