keel cooler in keel-repair and maintenance

[Bill Streever]

Hi All.

I am looking at an aluminum trawler with a dry stack exhaust and a keel cooler. I am more or less familiar with how ordinary keel coolers work (on shrimp trawlers for example), with heat exchanger pipes under the hull (usually recessed). In this case, the keel cooler is inside the keel itself. The broker did not seem to know how the keel cooler would be accessed for maintenance or repair, and I haven't found anything useful on line.

Questions:
1. Would I expect the keel cooler to consist of heat exchanger pipes that are sitting against the aluminum inside of the keel? If so, how would the pipes be protected from corrosion? Should I expect them to be aluminum tubes that are built into the keel?
2. Are keel coolers that sit inside of keels generally accessible for inspection, maintenance, and repair?
3. I know that idling an engine that relies on a keel cooler for long periods can cause overheating (because the water next to the keel cooler is not circulating). Is this even more of a problem when the keel cooler sits inside of the keel, so that there is no direct contact between the heat exchanger and the water? Also, would cooling be adequate in warmer waters?

Thanks for any thoughts or links to more information.

Hoping this trawler works out for us, but I don't want to move forward until I am comfortable with what I know about the keel cooler. -bill

 

[Bmarler]

Hi All.

I am looking at an aluminum trawler with a dry stack exhaust and a keel cooler. I am more or less familiar with how ordinary keel coolers work (on shrimp trawlers for example), with heat exchanger pipes under the hull (usually recessed). In this case, the keel cooler is inside the keel itself. The broker did not seem to know how the keel cooler would be accessed for maintenance or repair, and I haven't found anything useful on line.

Questions:
1. Would I expect the keel cooler to consist of heat exchanger pipes that are sitting against the aluminum inside of the keel? If so, how would the pipes be protected from corrosion? Should I expect them to be aluminum tubes that are built into the keel?
2. Are keel coolers that sit inside of keels generally accessible for inspection, maintenance, and repair?
3. I know that idling an engine that relies on a keel cooler for long periods can cause overheating (because the water next to the keel cooler is not circulating). Is this even more of a problem when the keel cooler sits inside of the keel, so that there is no direct contact between the heat exchanger and the water? Also, would cooling be adequate in warmer waters?

Thanks for any thoughts or links to more information.

Hoping this trawler works out for us, but I don't want to move forward until I am comfortable with what I know about the keel cooler. -bill

Without direct knowledge of how it was built you’ll be guessing how it was constructed. Aluminum is a great conductor though, so an internal cooler might be perfectly acceptable. I’m the event of a catastrophic failure, like the pipes leaking without any access, you could always fit an external cooler and bypass the original.
Surely, someone knows how it was built though. Is the builder still in business?

 

[Bill Streever]

thanks

Thanks.

The builder is no longer in business. It is possible that there are build specs aboard and that I might find something in the paperwork, but so far no luck there.

The current owner seems to know very little about his boat.

Is it possible that heat exchanger tubes are built directly into the keel, with coolant flowing through the tubes?

 

[dannc]

...
Is it possible that heat exchanger tubes are built directly into the keel, with coolant flowing through the tubes?

Yes having the coolant flowing through tubes, or a simple tank, against the hull plating is likely/possible on a metal boat. As was stated by another poster, AL conducts heat very well, so having the coolant next the hull plating is possible and likely.

Later,
Dan

 

[Circumnavigator]

It wouldn't surprise me if a section of the hollow keel is blocked off as if it were a tank and the coolant goes in one end and out the other. Very simple, the only potential failure is a failure of the keel structure (grounding?) or a failure of the joints where the pipes go in.


An idling engine doesn't produce much heat -- my experience is that on most trawler sized engines you have to put the boat in gear to get them up to normal operating temperature. Unless the cooler is badly undersized I would think it is fine to idle it, perhaps even while the boat is out of the water.


Jim

 

[jgwinks]

It wouldn't surprise me if a section of the hollow keel is blocked off as if it were a tank and the coolant goes in one end and out the other. Very simple, the only potential failure is a failure of the keel structure (grounding?) or a failure of the joints where the pipes go in.


An idling engine doesn't produce much heat -- my experience is that on most trawler sized engines you have to put the boat in gear to get them up to normal operating temperature. Unless the cooler is badly undersized I would think it is fine to idle it, perhaps even while the boat is out of the water.


Jim

I've seen plans for home building in steel where they did just that. The bottom part of the keel was blocked off to form a tank and coolant was piped in one end and out the other. The hull skin itself was the heat exchanger. With the thermal conductivity of aluminum this world be very effective

 

[dannc]

I've seen plans for home building in steel where they did just that. The bottom part of the keel was blocked off to form a tank and coolant was piped in one end and out the other. The hull skin itself was the heat exchanger. With the thermal conductivity of aluminum this world be very effective

I have seen some plans for steel boats, and the actual builds, which used half pipes against the hull plating. The coolant ran through the half pipes. I thought that was a good idea.

Other "keel" coolers are using simple tanks, which I think is a better idea, because it is simpler to build and less likely to have problems with the welds simply because there is less welding required.

AL transfers energy very well so it does not take as much area to cool down the engine coolant.

Professional Boat builder has an article or two on the calculations to figure out how area is needed to transfer the energy.

Later,
Dan

 

[Bill Streever]

Many thanks to everyone for your input. This is super helpful. I think I sent thanks individually to each response, but they are not showing up on the overall forum, so I'll try this quick reply feature to see if a public "Thanks!" shows up. Really appreciate everyone's willingness to share knowledge.