Air cooled engine with wet exhaust? - Page 3 - SailNet Community
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post #21 of 41 Old 01-17-2012
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It would seem the only real issue with the current system is a reliable section of flex as it is the only part that cant be solid

I would think the longer you can make the flex section the better its ability to deal with the motor movement

Going to a wet exaust will cause as many issues as it solves at this point

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post #22 of 41 Old 01-17-2012
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An air-cooled sailboat motor. Now that is a rare one!
The Deutz is a very reliable motor indeed. I have seen them run for incredible hours in the Middle East, in heat you would not believe.
The problem in using one on a sailboat is the enormous appetite they have for cooling air, and the ducting they will need to avoid cooking the cabin. They are a noisy unit, as they lack the water jacket that liquid cooled motors have.
If you wish to run a wet exhaust, then either couple a water pump to one of the pulleys, or perhaps use an electric pump separately. You need to be careful not to pump too much water though, as you can drown the exhaust. Logically, when the motor stops, so too must the electrical pump.

I guess you will never be short of cabin heat when the motor is running!
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post #23 of 41 Old 01-17-2012
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i'd agree. sounds like the problem here is stabilizing the pipes with adequate lagging and havind a nice stainless woven pipe, like a car for the flexi connection. Given the steel hull, exit temp is not the big concern as for a wooden or glass boat with a hot pipe sticking out the transom.

Still if water cooling the exhaust flow was a desired feature, and I personally would dig not having real hot pipes running through my boat's interior, one could install an engine fed or electical water pump, and :

1. install a lift muffler and the flexiblehose like bunches of boats and accept the inevitable corrosion from acid production as exhaust gases meet seawater.

2. direct inject water into the exhaust stream down stream (and downhill) from the exhaust manifold (corrosion again)

3. run a jacket around the exhaust pipe filled with flowing raw water with attention to desired angle and perhaps a backflow gate at transom or burble chamber upstream

4. run external copper tubing around the exhaust pipe al la a a glorified heat exchanger (probably not too efficient but might not be bad bedded in slilicon heat sink compound and a wrap of insulation

5. do 3 or 4 but with a keel cooler and expansion valve for safety as a closed loop.

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Last edited by ewoden; 01-17-2012 at 03:36 PM.
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post #24 of 41 Old 01-17-2012
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Quote:
Originally Posted by nsweeting View Post
. Right now, it mainly seems to be the flex pipe that begins to crack and leak. We originally got a broken section of it replaced, and it seems to have already developed new leaks. So a big questions is - how necessary is flex pipe in a dry exhaust system? Right now, our funds are not as good as they used to, so any kind of replacement we do will need to somehow be made with off the shelf parts.

stainless mesh flex pipe like this perhaps?
2.25" x 5" Stainless Steel Tripple Mesh Flex Pipe Tube | eBay

Here's another source: http://www.exhaustdepot.net/flexsection.html

This is apparently stainless exhaust bellows tubing wrapped in stainless mesh. Marine versions here: http://www.rosesmarine.com/products_exhaust.html

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post #25 of 41 Old 01-17-2012
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I've used an air cooled engine with a dry exhaust for many years. One diesel Mechaninic was quoted as saying "If everyone went dry exhaust and keel cooling ,us mechanics would all be out of work." Wet exhausts are a major source of engine problems. I met a couple in Tonga who went thru 2 engines since 1996 due to corrosion on valves form wet exhausts. They now have a dry exhaust.
I use sch 40 stainless pipe ,wraped in fibreglass house insulation then aluminium foil, then three inch wide muffler tape, coated with silicone caulking. After days motoring in the tropics ,it feels cool to the touch.
I have experimented with high heat silicone hose. At the head of my air cooled engine, at 3/4 throttler it didn't burn, at full throttle it did. Friends with a water cooled manifold tell me it lasts them 2 years at the manifold, at the transom it has lasted them 15 years with no problem.
I have a piece clamped on my dry exhaust 2 ft from the head, for a couple of years and it shows no sign of burning , so it appears the trick is to get it some distance form the head.
One could use the flat wound stainless flex , then silicone silicone hose over it , the stainless to take the direct heat and the silicone to stop any escaping gasses.
The more solidly mounted the engine, the less flexing your exhaust takes.

Last edited by Brent Swain; 01-17-2012 at 04:19 PM.
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post #26 of 41 Old 01-17-2012
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Quote:
Originally Posted by ewoden View Post
How so am I missing anything? Wet exhaust with water pump (belt or electric) would still apply yes? We are not talking about cooling the engine in this case rather cooling the exhaust to allow for a flexible coupling aft or running hot exhaust insulated aft).

You can run a dedicated open loop through sleeved pipe to cool exhaust without mixing and without a lift muffler. (AKA semi wet system). It gets done lots of times, even with air cooled engines.

How does that differ for a water cooled versus air cooled engine? The only issue I can see is running a water pump. That's no big deal, belt feed it like an altenaor just like any water cooled engine or run a dedicated electric pump. Many see advantages to a sleeaved exhaust versus a lift exhaust. Corrosion avoidance being one of them. Such a system would also achieve some measure of vibration damping, and the cost can be kept down by using internal pipe in stainless where the heat is but mild steel on the outside to allow for a more predictable corrosion resistence than one gets with stainless. In the last illustration: http://www.glen-l.com/weblettr/weble...nb-plate54.gif eliminate vertical stack, put the shebang on an angle to exit 22 inches above water line, replace engine source water with open loop from through hull to pump, to stern throug hull. incorporte other poser's vibration dampers and you are good to go. heck you get downstream to a point where exhaust may be cool enough to use exhaust hose for the final run to the transom. Oh and one avoids the power losses associated with lift mufflers.
Could you please show me in any of the links you googled and posted where there is any discussion on adding the necessary water pump?

That is my point.


BTW, take a look at the belt drive on a deutz- adding another belt to drive a water pump ain't that easy.

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post #27 of 41 Old 01-17-2012
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Quote:
Originally Posted by bljones View Post
Could you please show me in any of the links you googled and posted where there is any discussion on adding the necessary water pump?

That is my point.


BTW, take a look at the belt drive on a deutz- adding another belt to drive a water pump ain't that easy.
Haha well I can't. But my post was preceeded by one other mentioning the necessity for a pump and indeed one musn't be a naval architect to know that you are gonna need a pumped source of water to run a water cooled anything. Consequently, in the interest ofbuilding the exhaust and not repeating other poster's info/thoughts I figured I'd just help with some plumbing options. Incidentally, I didn't google them for this strings response as I'm building my own and have been toying with an aircooled auxilliary out of cost needs.

Regarding the belt drive, one can always run multiple power robbers with a single belt or is there some ABYC thing against that :-) . It would be the bracketry that would be the issue from my POV, but all would be moot with a electrically driven pump.

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post #28 of 41 Old 01-18-2012 Thread Starter
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Quote:
Originally Posted by Brent Swain View Post
I've used an air cooled engine with a dry exhaust for many years. One diesel Mechaninic was quoted as saying "If everyone went dry exhaust and keel cooling ,us mechanics would all be out of work." Wet exhausts are a major source of engine problems. I met a couple in Tonga who went thru 2 engines since 1996 due to corrosion on valves form wet exhausts. They now have a dry exhaust.
I use sch 40 stainless pipe ,wraped in fibreglass house insulation then aluminium foil, then three inch wide muffler tape, coated with silicone caulking. After days motoring in the tropics ,it feels cool to the touch.
I have experimented with high heat silicone hose. At the head of my air cooled engine, at 3/4 throttler it didn't burn, at full throttle it did. Friends with a water cooled manifold tell me it lasts them 2 years at the manifold, at the transom it has lasted them 15 years with no problem.
I have a piece clamped on my dry exhaust 2 ft from the head, for a couple of years and it shows no sign of burning , so it appears the trick is to get it some distance form the head.
One could use the flat wound stainless flex , then silicone silicone hose over it , the stainless to take the direct heat and the silicone to stop any escaping gasses.
The more solidly mounted the engine, the less flexing your exhaust takes.
Brent - thanks for your comments. From what I have seen, 500 degrees f seems to be the upper end of the limits of high heat silicone hose. Would I be correct in thinking this?
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post #29 of 41 Old 01-18-2012
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Around there. Yes, 500 sounds about right. You could stick a cooking thermometer under your lagging at various points to get the temperature, when bucking a headwind, or tied to a dock . It cools off a lot the further you get from the engine. I asked my father, a steam engineer, if going from a 1 1/2 inch pipe to a 2 inch would make much difference in exhaust temp. He said " A huge difference."

Brent Swain, Boat designer, Builder, and author of "Origami Metal Boatbuilding"
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post #30 of 41 Old 01-18-2012
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I must be missing something here ... the problem is multiple exhasut leaks. How is a water cooled exhaust going to help that ?

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