Wet exhaust lift

[Hawgwash]

What am I missing?
These pictures are a Perkins' in a 49 De Fever, stand up ER.
The mufflers must be at least 4 feet below the waterline.
I can't grasp how the water in the exhaust can travel up that distance and out.
Or, how the water does not back into the exhaust.
Tom?

 

[sunchaser]

HW

Good question and spot on observation.

On my similar, if not identical setup to what is pictured, the amount of water remaining in the exhaust run drain back is pretty small. I know this because on several occasions I have inspected the internals of the water lift.

Inside the water lift was about 2 cups of carbon (after about 1500 hours) and maybe six inches of water. Say maybe 1 1/2 gallons or so. This is pretty common for water lifts. With the 5 inch exhaust tube about 1/2 full of water for the roughly 3 foot tube column that seems to equate. Obviously the water lift has to be sized to sensibly accommodate the drain back volume.

One difference, our vessel has a siphon break on each exhaust due to low engine placement in relation to waterline. Not unlike thousands of sailboat setups.

 

[Keysdisease]

The height of the lift accomplishes two things, the higher the lift, the quieter the exhaust (without exceeding backpressure limits) and the high rise helps prevent backflooding.

Sunchaser is spot on about sizing, not as critical with propulsion engines because they are usually pretty big because they have to be, but on generator systems with separators properly sized lifts to accommodate the water in the lift pipe at shutdown is crucial. Some gen lifts are tiny, and can become full pretty easily.

Good question and spot on observation.

Obviously the water lift has to be sized to sensibly accommodate the drain back volume.

 

[Hawgwash]

I guess I'm hung up on volume. My head tells me if the hose was disconnected from the exhaust elbow, ahead of the muffler, it would fill a bucket pretty quick. So I visualize that water going into the lift muffler and wonder how it can climb that hill. Or is it mostly vapour?

 

[sunchaser]

HW

About 1.5 - 2 psi of exhaust pressure is used to move water uphill and out of the vessels exhaust.


Maybe towards the end of July we could take some recliners into our ER, sip a beverage and talk over this puzzler. Bottom line, size the lift muffler to take drainage water from hoses and be no more than say 1/3 full upon shutdown. Looks like DeFever did it just fine.

 

[Hawgwash]

HW

About 1.5 - 2 psi of exhaust pressure is used to move water uphill and out of the vessels exhaust.


Maybe towards the end of July we could take some recliners into our ER, sip a beverage and talk over this puzzler. Bottom line, size the lift muffler to take drainage water from hoses and be no more than say 1/3 full upon shutdown. Looks like DeFever did it just fine.

Now that sounds like a plan, I'll remember to bring my own pool cue this time.

 

[TDunn]

Another fact to consider. A column of water generates 0.4 psi per foot of height, so 2 psi of exhaust pressure can push a 5 foot water column.

 

[Capt.Bill11]

Not to mention that boat only draws between 4-5' of water I would think. So I doubt the mufflers are 4' below the water line.

 

[sunchaser]

Not to mention that boat only draws between 4-5' of water I would think. So I doubt the mufflers are 4' below the water line.

On my vessel the water column height is measured from the entrance to the water lift to the exhaust hose spill over point - about 3 1/2 feet add a potential stern sea of say 3 feet and easy to see a pressure design factor of 6 or 7'.

It would interesting to know Centek's test pressures.

 

[FF]

On a good water lift muffler system about the only noise the exhaust makes is the sound of the exhaust water falling.

I would think a larger muffler diameter might lower the exhaust pressure required to get the water up and our.

The largest danger with a small muffler volume is a no start situation ,

where the engine is cranked to prime and the exhaust continues to fill with water , until reaching a cylinder.

A drain to winterize can be used to empty the muffler if much engine cranking is required.

 

[Hawgwash]

I would think a larger muffler diameter might lower the exhaust pressure required to get the water up and out.

That is what got me thinking. Small hose into a large canister with a larger hose out and up.

I'm sure though, if I go camp out in sunchasers ER, he will easily show me how 3 stick men can be chased up a hill by one.

 

[Hawgwash]

On my vessel the water column height is measured from the entrance to the water lift to the exhaust hose spill over point - about 3 1/2 feet add a potential stern sea of say 3 feet and easy to see a pressure design factor of 6 or 7'.

It would interesting to know Centek's test pressures.

You read my mind and that isn't always easy as the old grey matter is covered in green stuff.

 

[Brooksie]

In addition to the rise of exhaust in the engine room that you have shown; if the exhaust hose can not pitch down to the transom and emerge above the waterline, then a "gooseneck" should be incorporated at the transom usually another 12"-18" of lift. This so that anchored in a seaway, the pitching does not roll water down the hose run, filling the waterlift muffler little by little, finally flooding the engine.
Of course a savy operator could open the muffler drain when anchored in the trades allowing the water to run to the bilge and be pumped out.

 

[Capt.Bill11]

It's amazing the boat/engines have lasted so long with all the flaws in the exhaust system.

 

[FF]

Having the engine exhaust open 100% of the time to a cylinder of water does seem strange.

But it seems to work, with care.

 

[sunchaser]

Having the engine exhaust open 100% of the time to a cylinder of water does seem strange.

Elementary my dear FF. Wet exhaust design 101.

 

[ulysses]

As a reference tool: the volume of water in a pipe or hose is .785 X Dia. (in feet)squared X 7.48. per foot of pipe in gals. So in a 4" hose it is .785 X .333 X .333 X 7.48 = .61 gallons. It certainly depends a lot on the temperature of the exhaust gasses as to how much of this volume turns to vapor during the cooling and discharge process, but I would imagine a significant portion.

 

[Ski in NC]

The water gets "splashed" up hill as a pretty turbulent exhaust/water mix. It does not need to be as much pressure as it would take to force the water uphill should the hose be full of water. One way to look at it is I can spit four feet up in the air, but have a hard time blowing 48" on a water manometer.

 

[sunchaser]

Further to Ulysses and Ski's points, water lift muffler sizing is based upon a shutdown situation with the the real non gaseous volume of solution safely stored to prevent an engine flooding situation.

But as FF noted several posts ago, too many cranking events with a no start and open sea cock can flood some wet exhaust designs.

 

[Hawgwash]

This thread and it's traction surprises me.
In an ok way.
When I posted, I thought it would get two replies both ending with the word "dummy."

 

[sunchaser]

HW

One the biggest issues with wet exhaust motor vessels is exhaust system layouts and builders not paying attention to the details. Cost to repair exceeds the cost of a Sarca or 5 to put it in perspective.

So yes, good subject.

 

[gwkiwi]

Not to mention that boat only draws between 4-5' of water I would think. So I doubt the mufflers are 4' below the water line.

My DeFever 49 RPH with 200hp Range 4 Perkins draws 5'7" and the exhaust hose is 26" from the top of the 12" high muffler. The mufflers are just below water line but not anywhere near 4' more like 8" to the top of the muffler and 18" to bottom of muffler, according to my measurements just taken.

 

[Hawgwash]

My DeFever 49 RPH with 200hp Range 4 Perkins draws 5'7" and the exhaust hose is 26" from the top of the 12" high muffler. The mufflers are just below water line but not anywhere near 4' more like 8" to the top of the muffler and 18" to bottom of muffler, according to my measurements just taken.

An element of optics then, I guess.

 

[Steve DAntonio]

Among the most common defects in systems like this I encounter is the lack of a continuous downhill run after the spill over point, the wet riser above the water lift muffler. Just about every engine and gen manufacturer out there calls for a minimum of 1/2" per foot downward slope or about 2 degrees. Many also include a minimum distance/drop between the water injection point and a water lift muffler, and a maximum lift height upon leaving the water lift muffler. I use this diagram to illustrate basic requirements to boat owners and installers, however I also caution them to follow precisely the instructions of the specific engine or genset manufacturer... http://www.northern-lights.com/media/PDFs/misc_pdfs/dont_drown_me.pdf

The Cummins installation manual, which is over 150 pages long, dedicates nearly 20 pages to exhaust systems alone.

None of this should be left to guesswork, Perkins published a manual called "Marine Installation Know-How" that walks installers through the exhaust system requirements, including required drop between injection elbow and muffler and required slope. Only engines that use a water lift muffler and wet riser can suffer from flooding caused by excessive cranking, dry riser exhaust designs, those that include a the continuous downward slope from the water injection point and an dry apex above the WL, cannot suffer from flooding as a result of extended cranking, as the water injected into the exhaust naturally runs overboard, it never has to be pushed up hill. Most genset installations on the other hand use the water lift muffler arrangement and they can experience flooding. I'm seeing some new gensets that include a placard warning users about this possibility. It can be overcome by either closing the intake seacock or removing the drain plug on the muffler during extended cranking.

Having temporarily installed a clear section of hose on wet exhaust systems on a couple of occasions to diagnose water/gas mixing issues, it's surprising just how much of the hose volume is gas and not water.

There is an entire ABYC chapter, P-1, on the subject of exhaust systems including, "P-1.5.11
The exhaust system shall be designed and installed to prevent cooling water, rain water, or raw water from entering the engine through the exhaust system under all normal operating conditions. The exhaust system design shall consider the drop height of the manifold above the waterline and a provision for downward slope of the exhaust system."

 

[Steve DAntonio]

PS

The primary fuel filters lack heat shields and metallic drains...

 

[Capt.Bill11]

PS

The primary fuel filters lack heat shields and metallic drains...

Or some one took them off so they could easily see what is in the bowls as well as easily drain them.

 

[Steve DAntonio]

Actually none of those filters are MA rated, all are Racor FG's, shipped without heat shields and metallic drains. The give away is the black support band and lack of blue MA labels.

 

[sunchaser]

Steve

Guidelines aside, I've struggled with how the metal heat shields are a fire preventer. If it were truly that relevant ABYC would not find plastic acceptable and recommend we all use metal canisters like Fleetguard.

There must be some logic I'm missing.

PS - there are two different styles of filters, Capt Bill is likely correct about removing the metal bowls on the one set.

 

[HiDHo]

I guess they realized that those with FG Racors would not buy MA rated filters to comply so a band aid approach is required. The heat shield and metal valve is on my to do list along with closing the fuel tank sight glass valves after taking a reading.

 

[Ski in NC]

I think the metal bowl is a heat shield so if you get an ER fire, the shield will give the plastic bowl more time before it is breached by heat. Protects plastic bowls from other fires, and gives more time before diesel is added to an already raging fire. That added fuel will make a bad fire worse, and also increase spill once the wreck sinks.

I think it is of marginal benefit, but not trained in fire research. If a fire is bad enough to melt an unshielded racor, mounted low in the bilge, good chances the boat is a total loss already.

I kept the shields on mine.

Maybe Cajun Rose will comment, he is restoring a boat that had an ER fire.

Dang, got a little off topic....