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HoffaLives 11-06-2007 09:21 PM

Wondering if this will work?
Not that there's already a shortage of things to do around here, but because I think most engineers got down on their knees to get their degrees, I'm always trying to figger out better ways to do things. Every boat has problem areas, and one place I hear about all the time is the raw water heat exchanger circuit. It's a bad concept IMO, and far, far more likely to give trouble than the freshwater part of the system.

Now given that (at least in this part of the world) we sail in damned cold water, water that is very reactive and tends to eat stuff, why are we sucking it aboard, running it through our trannys, engine and exhausts?

I'm wondering about taking the coolant from the freshwater circuit and running it through a section of looped hose epoxied against the inner hull. Glass is a reasonable thermal conductor and the water is maybe 8-9 degrees C, so the big question would be the surface area needed to conduct away heat to keep it below the boiling point.

Basically use the hull as a heat exchanger.

The thermal capacity of water is quite high, so I don't think you would need an outrageous length of hose.

I need to do some research on the surface area required, and the effects of heat on fibreglass. Anyone ever try something like this?

bestfriend 11-06-2007 09:22 PM

Aren't you on a five day downwinder?

JohnRPollard 11-06-2007 09:35 PM


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.

sailingdog 11-06-2007 09:38 PM

Hmm... you'd really want a better heat exchanger surface than fiberglass. Of course, if you ever had to motor in warmer waters, you'd be screwed. There is a thread on heat exchangers right now, which you might want to read.

haffiman37 11-06-2007 10:17 PM

That wheel has allready been invented long time ago:

Used in boats in both northern and southern hemisphare, particularly when ice blocking water-intake is a problem during winter!

Pub911 11-06-2007 10:53 PM

I like your thinking, Hoffalives. Damn the torpedos, keep at it. If not this one, another. Others are doing it, and making a good buck at it as well.
Look at the gadget that keeps you from having to take the whole damn water pump bolts out when you want to change the impeller. I know, modest in comparison to your proposed challenge, but innovative nonetheless. Or the refridgeration cooling loop that coils around the galley through-hole, using the up-and-down of the boat to circulate cool water around the coil as opposed to consuming power with an auxiliary raw water pump to do the same. I'm sure you've seen that in the back of CW or similar.
Now, some advice if you're willing to take it, explore the edges of your ideas. Step away from the raw-water circuit issue per se, and look at the solution - cold water all around you, moving, even when the boat's at rest, moving even faster when under way...what else could that do for you? I don't know the answer, but the approach is worth exploring - that is, ENGINEER IMAGINATION. Take the realities around you, benevolet or malevolent and exploit them.
Ok, it's late, enough L. Ron Hubbard impersonation for today.
Fair winds.

SVDistantStar 11-06-2007 11:59 PM

How about to reduce the drag of a keel-cooler, have it mounted in the lead keel? Its not an idea that would be retrofitted to an older boat, but say on a new boat have the cooling pipes in the keel when its molded. Ive wondered about this myself.

CapnHand 11-06-2007 11:59 PM

  • your hull is not glass, it's plastic reinforced with glass
  • plastic is not a reasonable thermal conductor, it's a pretty good thermal insulator

soul searcher 11-07-2007 12:20 AM

Realy not that bad of an Idea for a sail boat if you put the cooling circuit in the keel and not in the hull. a lead keel with a some sort of compatable metal
cooling grid cast into it would be a good thing. No drag like a conventional keel cooler. and would get the cooler into deeper water where its always colder.
put in a condensing circuit and you have a better refrigeration or A/C.
Maybe better to cast the keel out of steele and hang some lead on it.

HoffaLives 11-07-2007 12:54 AM

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.

As for the amazing sail we had, it was only Sidney to Victoria, which is about 5 hrs. You couldn't ask for a better sail, and it was so good to pull into the harbor as well, seeing the lights of downtown reflected in the water.

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