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Old 04-05-2008, 05:38   #1
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Tall drystack exhaust question

My spelling is bad and spell check isnt working ..sorry
I'm have trouble conforming to normal practices with my exhaust layout/dimensions.
My engine manufacturer recomends no more than a 40" rise of the exhaust due to back pressure.
Given my configuration I would have to lift the water lift up to high to have a safe distance between it and the engine exhaust.

I'm thinking to extend my exhaust drystack up about 3 ft +(behind my companionway ladder) do a "U" bend at the top, then inject the cooling water.
Then straight down with hose into the top of a water lift...this I'll fab. and will basicaly be a 10" dia fiberglass cylinder on its side.
The outlet FG pipe will extend down to with in an inch and a half from the bottom of the cylinder.
The outlet hose goes up to high spot (but lower than the dry stack) then slopes down until it exets the boat about 6" above the water line.

This is all pretty normal ecept for the extra high dry stack.
It seems that with the high spot being lower than the drystack that it would be almost imposible to ever flood my engine.

I know that I'll have additional insulation and vibration considerations but am sure I can deal with them.

Is there any other reason for not having an extra tall dry riser?
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Old 04-05-2008, 06:34   #2
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sounds like a good plan. I do have to ask, is there no where below the motor for the water lift? Also, are you sure the motor sits 40" below the water line? I've never seen one this deep on a sailboat. Even the Cheoy Lees and Hinckleys with the engine in the bilge are that low.
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Old 04-05-2008, 11:00   #3
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Tall drystack

The engine exhaust is pretty much at the water line
The 40” I speak of is from the bottom of the Water lift to the top of what would normally be the highest point in the exhaust before sloping down and heading out the hull exhaust fitting.
That highest point according to everything I’ve read, “should be well above the water line” (Nigel Calder) …..Depending on whom you ask….this should be at least 16”.
The problem is the only place I have for the highest point (loop) is against the hull, inside a locker.
Since I’m a sail boat, I get the gunnels wet…..Some times that loop will be under the water line ….
If I go below the engine I have to get under the shaft (above the shaft is too short to maintain a safe “drop”) the vertical distance from the bottom of the lift to the top of the loop is well above 80”. And like I said that loop is still not a safe height.
This is how it was before…a huge lift…..Additionally the size of the lift chamber needs to have a considerable capacity to receive (in Thierry) the volume of the 80” hose plus about 50%.
I have just replaced the original 30 year old engine….it must have had incredible back pressure (but it did last 30 years)

I really appreciate any input on this….I have studied marine exhausts hard over the past several months….but have not specifically seen this high riser/dry stack idea and am wondering why (did see some info on the Atomic 4 that looked a little similar.
I feel like I’m missing something BIG.
Help.
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Old 04-05-2008, 11:35   #4
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Tall dry stack

After re reading my last bit I’ve edited it for clarity…sorry.

The engine exhaust is pretty much at the water line
The 40” I speak of is from the bottom of the Water lift to the top of what would normally be the highest point in the exhaust before sloping down and heading out the hull exhaust fitting….lets call it the loop.
That height of that loop, according to everything I’ve read, “should be well above the water line” (Nigel Calder) …..Depending on whom you ask….this should be at least 16”.above WL
The problem is the only place I have for the loop) is against the hull, inside a locker.
Since I’m a sail boat, I get the gunnels wet…..Some times that loop will be under the water line ….
To get below the engine exhaust with the lift muffler, I have to get under the shaft (above the shaft is too short to maintain a safe “drop”)if I go under the shaft, the vertical distance from the bottom of the lift to the top of the loop is well above 80” (plus a reasonable horizontal length to get to the side of the hull. And like I said that loop is still not a safe height.
This is how it was before…a huge lift…..Additionally the size of the lift chamber needs to have a considerable capacity to receive (in Thierry) the volume of the 80” hose plus about 50%.
I have just replaced the original 30 year old engine….it must have had incredible back pressure (but it did last 30 years)

It just seems like having the dry stack really high in the center of the boat and the loop at the side of the hull a good bit lower…is almost bullet proof.
Even if I crank over the engine excessively and forget to close the raw water (like someone did on the old one and flooded the engine) the water in the exhaust can never build up high enough to get over the dry stack.

I really appreciate any input on this….I have studied marine exhausts hard over the past several months….but have not specifically seen this high riser/dry stack idea and am wondering why (did see some info on the Atomic 4 that looked a little similar.
I feel like I’m missing something BIG.
Help.
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Old 04-05-2008, 12:51   #5
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What your proposing is a viable option.
What is the displacement of your engine in cc's? What is the drop from the injection elbow to the water lift in stock configuration?
The high loop can go against the hull side without problems? Are you healing that far under power? if so I'd be more worried about the oil system than the exhaust.
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Old 05-05-2008, 01:26   #6
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Tall dry stack

The new engine is from Mermaid Marine, out of the UK.
It’s a JCB 444 series (J444)
Naturally aspirated 4 cyl. 4399 cc.

http://www.mermaid-marine.co.uk/PDF/Mermaid/JCBJ444.pdf

The distance from the water injection elbow to the bottom of the previous/original lift muffler was around 3ft….that put it setting in/on the bilge under the prop shaft.
Since the water injection is right at the WL, the bottom of the lift muffler is around 3ft below the WL

The exhaust hose then came out of the top of the lift muffler at a slight angle and followed/rested on the side of the hull athwart ship all the way out and up to with in 6” of the underside of the deck.

From there it made a fairly tight “U” bend back down (180deg stainless fitting…the loop) then gradually curved aft….sloping down and traveling another 8ft or so until it exits the hull 6”above the WL

You absolutely right on the engine oil…I don’t expect to be motor sailing with the gunnels in the water.
But I do want to drop the loop so its at least a foot lower than the dry stack…maybe more….I think its only function now is to be high enough to insure a good slope to the hull exhaust…..so as not to have to push that water as well.

The big question I have is, if it’s such a good way to do it….why don’t I see anyone doing it that way.

Also …if the injection elbow on the dry stack is just after the 180 elbow…that’s pretty high…..I don’t think I would need to have a siphon break on it…I don’t see how the stack could ever have that much water in it …..Remember it will get over the loop first as its lower…Right???
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Old 05-05-2008, 02:24   #7
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I just installed a 4" exhaust for my John Deere 4045 and with the engine sitting just above the bilge I was able to fit a large water lift muffler under the floorboards just in front of the companionway steps and loop the exhaust up alongside the quarterberth to an outlet tucked under the stern (Picture in my blog).

All this came within the recommended envelope.

Would it be possible for you to lift the muffler to the recommended height?

I am a little nervous about a following sea going up the exhaust but have never heard of this happening. If I experience problems I will make up some sort of surge tamer.

I try it out tomorrow with a 4" outlet.
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Old 05-05-2008, 03:12   #8
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Tall dry stack


I had a look at the muffler pic on your blog…This could be done on mine boat but it doesn’t give me enough of a drop between the injection elbow and the top of the muffler. According to what I’ve read 12” to 18” and some are adamant that 18” is an absolute minimum.

What distance do you have from the actual point of injection to the TOP of your muffler.

I was thinking of going with a 3” in and out of the muffler. 4" seems big.

I see lots of surge tamers, seem like a good thing…also should be an easy fab job.

Did you just install that engine…the transmission looks new.
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Old 05-05-2008, 03:25   #9
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I had a look at the rest of your site….nice
I see you did put a new engine in…also nice!
But I don’t know about that drop from the water inlet….it looks a bit short?
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Old 05-05-2008, 20:34   #10
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James,
The original install sounds correct. The drop should be 12" min to the water lift.
With 4L of displacement I'd like to see 3" in 4" out or all 4" if possible. Using 4" will decrease the back pressure also.
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Old 06-05-2008, 03:32   #11
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The problem with the original exhaust set up was that it made my lift over 80” high, this is twice what is recommended from the new engine manufacturer.

I have seen many recommendations for increasing the outlet size of the muffler to counter resistance fromany bends or water lifts…and it sounds right.
Amazingly I have found almost no off the shelf mufflers with this feature.

My outlet from the engine OD the jacket is only 2-1/2 “ now so I figured 3” would be fine?
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Old 06-05-2008, 04:54   #12
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find out if the new engine as a recommended value for exhaust back pressure.
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Old 06-05-2008, 05:25   #13
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What is this valve and where would it go.
I haven’t heard of this.

As far as discussions with them go regarding the exhaust system. they have confirmed the 40” lift as a maximum...and that's about it.
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Old 06-05-2008, 05:31   #14
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I've tried to explain several times what you proposing will work, but it's not standard. You appear focused that it is the way to go.

Every engine manufacturer in the world has a nominal value for acceptable back pressure.

If the old system functioned for 30 years, and the new manufacturer is telling you it's deficient. Have them give you a design that is acceptable. I'm not going to design your exhaust over the internet, half a world away. Only to get bad mouthed in 3 years because something went wrong.

Good luck with the project.
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Old 06-05-2008, 06:27   #15
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Thanks for your help with this.

I guess I’m looking for input that will help me talk myself into or out of this Tall Drystack idea.
You’re right….so far I see no fundamental problems with it and as of now will press ahead.
I’m going to the boat (in a different country) next Tue. for a week and will be fabricating it as discussed.

Thanks again for your input.
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