Cool Running: Managing Heat in Interior, Fridge, & Engine Room

The stop in Acapulco was brief. Eighteen hours to clear out of Mexico with the port authorities, top off the fuel tanks (again at US$2.40/gallon) and check the engine room.

The latter revealed that the raw water pump on the port engine had begun to leak sea water and oil from its shaft seals. This is just a couple of hundred hours after the starboard pump was changed, so we now know to rebuild these after 2000 hours. There is a spare on board and the R and R took half an hour. Everything else looked fine.

We’re crossing the Gulf of Tehuantepec as this is being written. Conditions are perfect, four to eight knots of breeze from the aft quarter and calm seas (just as predicted by our Expedition routing software and GFS weather model GRIB files). Water temperature has been between 85 and 87 F (29.5 to 30 C), air temperature the same in the evening and a little warmer in the sun.

The heated environment stresses systems and potentially crew, unless the correct precautions are taken.

With an Unsailboat we have the luxury of power 24 hours a day, which translates into AC electricity for air conditioning. So the interior is a cool 76 F (24.5 C). But with our modest air conditioning capacity (kept on the light side so we can run it off our inverters) and huge heat load from the array of windows surrounding the “great room” we have to reduce heat load on the glass.

This takes two forms. First, the windows have a 3M nonmetallic film on them which eliminates 99% of UV A and B radiation, and more important for the air conditioning, half of the infrared (heat) radiation. In addition, we have a set of awnings which fit around the perimeter. These are zipped to the handrail around the house edge and then tied to the lifelines. Early and late sun pokes under these awnings so at each end of the day the inside window shades on the affected area are partially dropped (we can see under them when seated).

Until three days ago our sailing habits were dominant and we were barely using the air conditioning. Instead we were relying on natural ventilation through the deck hatches and aft door (which is excellent). The air flow kept the 86+F (30C) inside temperature tolerable (barely) and really stressed the fridge and freezer systems. As a result, the variable speed Frigoboat compressors have been running flat out trying to keep up. The basement freezer was slowly losing the temperature battle. Checking with Frigoboat we found that our 100% full freezer did not allow sufficient air flow to the evaporator plate. With the air conditioning controlling the interior, temperature is holding now, and in the next day or so we will reorganize to get some of the inside surface of the evaporator plate exposed.

Designing an engine room for hot operation is a tradeoff. It is almost impossible to do it with natural air flow. Using forced ventilation, with big blowers, creates a huge source of noise, and if the blower(s) fail, you are really in trouble.

With our large engine room volume and small engines we have the option of maintaining temperature with the engine room hatch opened (in addition to the Dorade style vents). We wouldn’t do this in heavy weather, but that is rare and if we were forced to close the hatch we would live with inefficiency of the high temperatures. As it is, with the passive system we are using, the engine room averages 120 to 125 F (49 to 51.6 C). And it is a great place to lose weight from sweating if there any chores to be done.

Speaking of which, our hydraulic system generates a lot of heat which is dissipated via two heat exchangers. One of these is on the case drain lines to the hydraulic pumps and the other on the reservoir tank. These were plumbed in parallel, with the raw water cooling circuits off the engines providing the coolant. The system has run fine through the previous 2700 hours of operation, but in this hot water we were starting to see overheat alarms on the NAIAD stabilizer system.

Discussing this (via e-mail) with Don Redding of NAIAD we learned that they no longer recommended a parallel plumbing set up on the heat exchangers, now suggesting having them in series. As the present system use 1/2″ fittings and we needed 3/4″ for series, we were not sure we could execute this modification under way. However, digging into the large box of fittings carried in the basement yielded a functional (albeit less than perfect) handful of parts to allow the change to be made. The result is much better water flow and lower hydraulic oil temperature.

Meanwhile, the crew is finally into the routine, sleeping well, and enjoying the process of watching the waves slide by. There is nothing on the horizon but ocean. No clouds, little wind, tiny wind waves and a moderate beam swell. Motion is negligible, engine noise barely audible over the whisper of the air conditioning (in fact the air con seems to mask what engine noise there is). We are running at 1850 RPM, which is where we find the fastest speed for minimum noise. This is yielding an average of 10.5 knots – although right now we are losing almost a knot to current. The flying bridge is a favorite haunt day and night.

Our ETA for Balboa, Panama in just under five days.

Posted by Steve Dashew  (April 21, 2008)

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