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Go Back   SailNet Community > On Board > Gear & Maintenance
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  #11  
Old 11-07-2007
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I worked on a house- solar\conductive heat. It had a grid of something like abs plstic set in the concrete foundation that kept the floor warm and warm air went up through the house. the trick on it was alot of very small tubes running long distances with low preasure and low flow.
It will work Hoffa but the one off, set up, would probably cost more than a new heeat exchanger and a new water pump X 5 .
the problem on the boats I worked on that were keel cooled were that the cooler was generally the stacked plate variety and barnicals and alge growth on the plates was what would kill you. It has to be a cooler that is inside the hull or keel to be maintanace free. on a steele or aluminum hull the cooler could be very efficiant. you would have to figure the surface area of the heat exchanger and the amount of cooling efficiancy of the raw water pump flow. You would have to embed a grid into the hull the insulating properties of the hull and water and hull and air may heat the air in your hull up more than the water around it depending on ambiante temps. heat generaly rises.
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  #12  
Old 11-07-2007
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Of course, any large heat exchanger grid that you setup would probably make a very nice SSB antenna ground plane.
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  #13  
Old 11-07-2007
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Quote:
Originally Posted by HoffaLives View Post
I thought about the keel cooler thing but didn't want those holes in the hull. I did some quick checking, and the k-value or thermal conductivity of GRP is about 1/2 that of water, which really isn't that bad (and a long way from being an insulator). The hull of the boat is in intimate contact with an enormous heat sink. It CAN be done (and there are high heat transfer epoxy resins out there (ie. TIGA R-915, K=1.46, H2O=.5 ). The issue is how big of a heat diffuser you would need to sufficiently conduct away the heat. You could build a diffusing grid on the inside of the boat using the above epoxy and glass.

The temp of the cooling water is below the boiling temp of water, waaay below any ignition temperature.
Hoffa,

Even if the K-Value of GRP is 1/2 that of water, the volume of water being pushed through the heat exchanger as compared to the surface area of GRP in contact with the closed loop would make the delta between the respective abilities of these systems to cool exponential. Your fibreglass may be transferring some heat into the water through the exterior surface of the hull (and also quite a bit of heat into the INTERIOR of the boat through the air), but it is not FLOWING over the closed cooling loop like the raw water does.

Some of the other variations on the keel-cooler are interesting and I think they've all been tried with varying degrees of success. Usually what the workboats do is simply run a copper pipe longitudinally outside the hull, parallel to the keel, for a run of about six or eight feet. You also have to adapt the system to a dry exhaust.

Bolger and others have taken it even further in certain designs and eliminated even the keel cooler by going with vented air and oil-cooled engines with dry exhaust.

Last edited by JohnRPollard; 11-07-2007 at 11:10 AM.
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  #14  
Old 11-07-2007
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car radiator

Hello,

If you are so concerned about the effects of raw water, why not just get rid of the heat exchanger, raw water pump entirely and go a standard automotive radiator? You would need to place it somewhere and install a fan to blow air through it, but you get rid of a water pump and extra plumbing. It works fine for cars, there is no reason why it would not work on a boat.

Barry
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Old 11-07-2007
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Quote:
Originally Posted by BarryL View Post
Hello,

If you are so concerned about the effects of raw water, why not just get rid of the heat exchanger, raw water pump entirely and go a standard automotive radiator? You would need to place it somewhere and install a fan to blow air through it, but you get rid of a water pump and extra plumbing. It works fine for cars, there is no reason why it would not work on a boat.

Barry
I've actually seen this done... a monstrous 65' steel ketch built from one of Roberts' plans. Unfortunately the boat burnt up before the system was really put to the test.

I'd suspect that the space required is the major negative - fab noise another and heating up of the interior, while welcome at certain times and in certain climes, not so much at other times.

And besides, it's just not nautical ......
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Old 11-07-2007
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Barry...

The problem is the collosal amount of heat to be rejected.
A 35 hp motor operating at (say) 40% efficiency will be rejecting about 65 kW into the cabin.
You will just cook the crew.

It would be possible to make a big cowl that ducted the heated air out and into the air, but it would mean a big through-deck, and it would be a sinking risk in heavy weather.

If I were going to go the route of the cowl, I would have an air-cooled motor, and a big duct. The super-hot exhaust manifold would be the next problem... it would get seriously hot.

Air cooled motors are noisy too. I know Magirus Deutz make a few good ones. Lister used to, and probably still do.
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  #17  
Old 11-07-2007
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Quote:
Originally Posted by BarryL View Post
Hello,

If you are so concerned about the effects of raw water, why not just get rid of the heat exchanger, raw water pump entirely and go a standard automotive radiator? You would need to place it somewhere and install a fan to blow air through it, but you get rid of a water pump and extra plumbing. It works fine for cars, there is no reason why it would not work on a boat.

Barry
This is essentially what I was describing in the last pararaph of my previous post, except adapted for the marine application. Autos have the huge advantage of their engines being mounted externally, and having massive air flow over the radiator surface at loaded operating speeds (supplemented by fans at idle). In a sailboat, even if you mounted the radiator externally, you wouldn't have the same volume of air moving across it. Usually the air cooling of the coolant (via ducts and fans) is augmented with a jumbo oil reserve and separate air-cooled oil cooler.

It's not a very practical approach for cooling a small boat engine. Not to mention the added complexity of mufflers etc for the dry exhaust, along with the fumes and heat.
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  #18  
Old 11-07-2007
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This is turning into another "Could a fan in front of a sailboat improve sailing?" thread.
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  #19  
Old 11-07-2007
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Hey TB,

Don't mock the "SailFan"! Just because you're stuck in your ways doesn't mean the rest of us have to be. I'm going to be posting an update soon on the SailFan experiment and when I do I'm sure you wll be amazed at the progress of this ingenious invention....
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  #20  
Old 11-07-2007
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Quote:
Originally Posted by JohnRPollard View Post
Hoffa,

Sorry, but it won't work. I'm not sure which would happen first, but you would either ignite your fibreglass or toast your engine. The fibreglass hull will not adequately conduct the heat out of the system no matter how cold the water is.

What you COULD do, and many engines particularly those on work-boats have been configured this way, is run the closed coolant loop OUTSIDE the hull and create what is called a "keel-cooler". They work extremely well, but most sailors find the additional drag unacceptable (as opposed to motorboaters that are always under mechanical propulsion.)

I commend you for thinking outside the box. However, as imperfect as the heat exchanger may be, it's not so bad either.

Yes, I believe that is how Nordhavn cools their engines. However, the exhaust still comes out quite hot.

- CD
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