Skeg Cooling

[savell]

Hi. I was looking at a metal boat and the owner informed me the skeg was full of anti freeze and that was how the engine was cooled. He thought it worked so well it almost did Not get to op. temp. Is this a common way of cooling? I have never heard od it. Thank you.

[valhalla360]

I believe he is talking about keel cooling.

If done properly, it can be fine
- Advantage, you eliminate a thru hull and the complications of passing sea water thru a heat exchanger and potential leaks.
- Downside is it doesn't transfer heat as efficently. Assuming a small low power engine and a proper design, that isn't a problem.

[Sailmonkey]

It works so well that the vast majority of workboats are cooled this way. ICW towboats have keel coolers recessed in their hull sides so they can take the ground, shrimp boats have rows and rows of keel coolers for the engines and the refrigeration.

[Cheechako]

Interesting concept.. put it in the skeg!

[jannw]

Keel cooling makes a lot of sense when combined with a dry/hot exhaust - no need to pump corrosive hot sea water through your engine at all!

It makes a lot of sense in a metal boat ... and is how most commercial metal boats engines are cooled. Just got to get the sizing right!

[Cheechako]

Yeah, dry exhaust is the rub in a sailboat. Need a metal muffler to quiet it down, bellows to allow movement, insulation etc.
I helped design/build some small boats for the armed forces that had two 6 cyl diesels in them. Keel cooled and trailerable. We must have sized the keel coolers too big as they could run forever on the trailer and the air cooled them fine.! Running 15 mins out of the water was a requirement.
The SS mufflers had a limited life though, and boy did the engine cavity get hot.

[TeddyDiver]

Originally Posted by savell

Hi. I was looking at a metal boat and the owner informed me the skeg was full of anti freeze and that was how the engine was cooled. He thought it worked so well it almost did Not get to op. temp. Is this a common way of cooling? I have never heard od it. Thank you.

Around here keel cooling and dry stack is the norm, don't know many boat's with wet exhaust. The main reason is winter and freezing temperatures. Adding a thermostat in the cooling circuit helps getting proper operating temperature. It's also quite easy to have water jacketed exhaust manifold and a part of the exhaust tubing before the muffler which helps with engine room heating and corrosion. Dry stack should be also isolated properly.

[Pauls]

You should consider the skeg cooling a plus point. Salt water cooling, with all of the failure modes associated with it, is probably the #1 cause of engine failure on boats. The skeg cooler eliminates the hull feedthru, raw water pump failures, cooling system clogging by sucking in whatever, cooling water backing up into the exhaust system when the engine is cranked for too long without starting (which can bend a rod), etc.

It is not difficult to insulate a dry exhaust. Either rock wool or fiberglass, covered with an outer shell of lagging, works very well. Done right, the engine compartment will not overheat.

How much trouble do you have with the dry exhaust on your car? The same system in a boat can be just as reliable. As previous posters have said, this is the norm for commercial boats. They're out on the water more in a month than most yachts are in a year.

[savell]

This should be a pic of the exhaust wrapping

[savell]

By the way. Thank you all for your replies. They helped a lot. The way the owner explained it to me was that the skeg was hollow and was filled with antifreeze. But the external tubes wrapped around it makes more sense. I have not seen the bottom yet. The boat has been around the pacific so it must work well.

[Jesse]

I saw a skeg cooler on a wood work boat about 50' and built in the late forties. The owner told me it was a welded assembly of 1/2'' steel with 5 stacked chambers with the hot water going to the lower chamber first then back to the engine through the other chambers. It was about 4' long and probably 5'' wide and triangular shaped with the rudder hung from the aft portion and looked like every other skeg I've seen. He said it could not be painted and had to be re-plated every dozen years or so.

[Pauls]

Savell, is the boat you are looking at one of Brent Swains designs? This is the way he does his cooling systems. There are a couple hundred of these boats in the water, it works fine. A very efficient way to cool an engine, no added external drag, no power consumed driving a raw water pump.

[savell]

Yes..it was a BS 36

[jannw]

ahhhh ... if you are looking at a Brent Swain boat you'd do well to buy his book, and read it through a few times. He has some odd ideas, but also some very good ideas, and the proof is in the pudding (meaning the boats, they work!).

[TeddyDiver]

A bit of care is in place considering any BS boat. First there might be some other structural issues considering either the engineering made by Brent (no engineering what so ever, just assumptions) or the building quality. All of these boats are DIY with a whole spectrum of builders from a competent boatbuilder and welder to a complete jackass and anything between. Some of the boats are foamed and there might just rust benieth.. or perfect steel, you never know.
BR Teddy