Boiling the Heat Exchangers

Adam had asked what I meant by "boiling the heat exchangers, so I thought I'd write an entry about it.

 
 
You probably already know all about heat exchangers, so just skip over this paragraph and the next one if so. As you probably know, there are various pieces of equipment on a boat with oil or water or hydraulic fluid that needs to be cooled. Often, cooling is provided by seawater being drawn through a heat exchanger. The heat exchanger takes some of the heat from the equipment's fluid, and passes that heat on to the seawater, which is then pumped overboard. The heat exchanger consists of small tubes that pass the equipment's fluid very close to the seawater, while keeping them separate from each other.

The trouble is, stuff grows in seawater, and it grows in warm seawater even more. So, the combination of small tubes and warm seawater means that all "raw seawater" heat exchangers eventually clog up. Not all at once, but gradually over a period of time that might be a year or might be 5 years, or might be 6 months, just depending on local conditions such as temperature and "how much stuff is there in the water". As the clogging up occurs, less and less seawater goes through the exchanger, and it becomes less and less effective, ultimately becoming completely clogged and completely ineffective.

One way around this problem is to not bring seawater aboard at all. Instead, a warmed "loop" of water or coolant is sent outside the boat to be cooled in a "keel cooler" that is attached to the outside of the hull. This keeps the seawater outside the boat, and the heat exchangers clean. However, I'm told that keel coolers can also clog up on the outside of the boat, and sometimes in a matter of a couple of weeks. Ken Williams reports about this issue in his excellent blog.

Anyway, to remedy the heat exchanger clogging problem, it is necessary to somehow remove the build-up. It turns out a very effective and fairly easy way to do so is to use a solution such as Barnacle Buster to dissolve the build-up without harming the exchanger itself. This is called "boiling" the heat exchangers, because the dissolving action effervesces (kind of like Alka-Seltzer), and so looks like boiling water.

 
 
Sometimes it is easiest to remove the heat exchanger and put it in a bucket of Barnacle Buster (or similar) solution. Other times, it is easier to undo the inlet and outlet hoses from the thru-hulls, and just let the equipment's pump pull Barnacle Buster from a bucket, through the hoses, into the equipment, and back out again into the bucket. There are hybrid approaches too. Either way, in a couple of hours (maybe a bit more in a hard case), the clogs are all gone, and the heat exchanger can work properly again.

 
 
When I bought it, my boat was about 2 years old, but had only been owned by the manufacturer, who had run it up and down the East coast to boat shows. My engine had something like 600 hours on it, and my gensets had about 250 to 300 hours on them. I had 8 heat exchangers to consider. One for the main engine, one for each genset (2 in all), one for the hydraulic stabilizers, one for each power take-off for each genset (for the get-home drive), one for the power steering, and one for each of the two air conditioner "tempering units".

Of these, the air conditioners needed the most cleaning, because they ran much of the time when the boat was just "sitting", even when the engine wasn't running. The engine and gensets weren't too bad. The steering was fairly clogged for some reason, and so were the stabilizer. We came to the conclusion that a combination of "hours" and elapsed "days" of sitting/operation all combined to gradually clog up the system. 

Please note: all the temperatures in my boat were absolutely normal, so the system was not so clogged up that things started to overheat. However, the writing was on the wall, and sooner of later, something would have overheated and shut itself down (hopefully) to protect itself. As you know from my previous writings, my philosophy is to stay "ahead" of the boat on maintenance, figuring that it is both cheaper and much more pleasant to fix things before they break and before the family is aboard for a scheduled trip, than to fix something in a seaway when everyone is uncomfortable. I'm also not sure it's actually cheaper to do this, but it may well be, since all repairs can be done "at leisure" rather than on an "emergency call out" basis inevitably at 5pm on the Friday of a long weekend.

I will say this much: In the hot, humid Florida climate, my air conditioners were running constantly. The day that the heat exchangers were cleaned, the air con started to only run about half as much, but the boat stayed just as cool. The improvement in heat exchanging was very visible at the air con overboard drain, where at least twice as much water came out as had come out before.

Bottom line: Part of what I've done with this boat is to bring it up to better-than-new condition, and to take preventative steps to ensure a good "dispatch reliability" of the boat (ie: to ensure that when I want the boat to go, it will go). This involves replacing slightly more parts than usual, slightly more frequently than usual. I learned this from my days as an aircraft owner, and am trying to carry the same methodology over into boating.

It is fair to say that perhaps the best part of this boiling exercise is that it all happened in Ft. Lauderdale while I was comfortably at home in Honolulu. This is one of the benefits of working with a wonderful captain who is helping us through the early months of our ownership learning process.

Current Blog Article: Boiling the Heat Exchangers

Winter 2011: Training from Lauderdale to Georgetown and back!
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