PT40 exhaust system

[Paul Swanson]

There have been some 40 ft. Pacific Trawlers with 5.9 liter Cummings engines that have experienced engine damage from water entering through the turbocharger into the cylinders. I looked carefully at my own installation and determined that the external water line was only inches below the turbo and inlet to the exhaust manifold. Furthermore, the static water level in the water lift muffler after shutdown was less than one ft. below the turbo. According to most experts the turbo should be considerably higher than this to provide a fail-safe exhaust system. I was quoted about $2500 for the S/S plumbing to raise the turbo on my boat.

I decided on a completely different approach which consists of a drain hose connected to the bottom of the water lift muffler and a simple normally open solenoid controlled valve connected to the “ignition” switch. When the engine is started the valve closes and the exhaust operates normally. When the engine is stopped the solenoid opens the valve and the water drains out of the muffler into the bilge and is carried overboard by the bilge pump. Any water that should enter the exhaust system inadvertently simply drains into the bilge. I can find no weakness in this system and the total cost was less than $50.

Paul

 

[Jay N]

Hi Paul.


Seems like an practical solution, although it does raise the complexity of the system and introduces possible flooding into the bilge.


My 6BT5.9 installation has the turbo about 5 inches above the waterline. But the water injection location is about 14 inches above that. Then there is a gentle decline to a surge chamber, in-line muffler and then a run to the transom.


On my PT37 (Hull #3), the height of the original engine (Bedford 150) required a chunk of space from above the galley deck level, and they installed the higher exhaust line with the 6BT5.9.


One of the problems with having a long exhaust run to the stern, is the amount of water in the exhaust line that can overwhelm the amount of space available in the muffler. So, if the engine is not operating, and the boat is pitching, it is possible to get water into the engine.


The best solution (if possible) is to raise the level of the water injection which should preclude most potential flooding situations.


Also consider the need to plug the exhaust system to isolate the engine should you need to be towed. I carry a plug that can easily be fitted at the transom.


$2500 seems pretty high, but I don't know exactly what that includes. And I'm not that familiar with the newer boats' engine installations, or with engines other than the 6BT5.9 that I have.

 

[High Wire]

If the sol fails to close with the engine running, it could also dump diesel exhaust and carbon monoxide into the boat.

 

[Art]

With engine off - Decreases / virtually eliminates back-wash water ingress from actively intruding stern water pressures (wakes and such); should also work on side exhaust exits:

External Flapper

Hardin Marine - 5" to 6" I.D. External Flapper

 

[bayview]

With the water lift and low riser IMO you need to be careful of cranking the engine without it starting just as with a generator and muffler.

 

[bayview]

dirty exhaust water into your bilge, really?????

 

[Keysdisease]

If you had a place higher above the waterline you could install a small separator that would drain all the water from the system aft of the separator. Any water coming back up the exhaust would drain out the separator rather than into the lift.

"a place higher above the waterline " could be a cockpit locker, the void space between the hull and the cockpit inner liner, etc.

 

[Paul Swanson]

The drain at the bottom of the muffler has an approximately 1/8 “ hole so the possibility of flooding or CO poisoning is nil. It takes about one minute to drain after shutdown. There is about a gallon of saltwater that goes into the bilges and is pumped overboard. The saltwater is indistinguishable from the ocean water; that is, isn’t ”yucky”.

There are two ways water can get into the engine. One is through the raw water inlet, through the engine and into the exhaust water injector. This is generally protected by a loop well above the water line and an anti-siphon valve. If the anti-siphon valve fails the water can siphon into the muffler, fill it up and overflow into the engine itself. The second way is through the exhaust pipe at the stern. Strong waves, being towed backwards, or a strong current along with a failed flapper valve can drive water through the exhaust system, again filling up the muffler and flooding the engine.

In my 2002 PT40 the exhaust between the muffler and the stern exit has about a 2 ft. vertical loop so the second mode is unlikely and the anti-siphon valve and loop in the raw water side looks robust. However, both late model PT40s that I know of that have had their engines damaged had a Cummings approved installation similar to mine, yet they still failed. Repair costs ran into the $20,000+ range.

 

[Keysdisease]

I would think your engine is fresh water cooled and therefore very little chance if any for salt water to get into the engine or the exhaust through the raw water cooling system.

If you are raw water cooled than water has to get past the pump to get into the engine

I think

 

[Paul Swanson]

I would think your engine is fresh water cooled and therefore very little chance if any for salt water to get into the engine or the exhaust through the raw water cooling system.

If you are raw water cooled than water has to get past the pump to get into the engine

I think

The raw water dumps into the exhaust downstream of the turbocharger. It is possible (and indeed happened) for the raw water to back up, filling the muffler and flowing back into the engine through the exhaust manifold and any open exhaust valves. That pretty much destroys the engine. The way to prevent this is for there to be a riser between the turbo and the place where the raw water is injected that is high enough so that water cannot flow back into the engine. my engine does not have a riser that is high enough...or so the experts have told me. The plumbing for such a riser must be made of stainless and well insulated. I was given an estimate of $2500 for the fix, hence my somewhat unique workaround.

Paul

 

[DavidM]

Paul:

I hate to rely on something electrical/mechanical for safety on a boat. On our long gone Mainship 34T there was an equalization line (for lack of a better term) from the bottom of the lift muffler to a thruhull below the water line. That line, about 3/4" in diameter assured that the water level in the lift muffler could never get above the outside waterline. That left the water about 6" below the turbo inlet, so it was safe.

There was nothing that needed to be done to make it work. Maybe some exhaust particularly at high loads would blow out that equalization line, but so what, no harm.

So think about plumbing it this way overboard and eliminate the solenoid valve.

David

 

[High Wire]

Paul:

I hate to rely on something electrical/mechanical for safety on a boat. On our long gone Mainship 34T there was an equalization line (for lack of a better term) from the bottom of the lift muffler to a thruhull below the water line. That line, about 3/4" in diameter assured that the water level in the lift muffler could never get above the outside waterline. That left the water about 6" below the turbo inlet, so it was safe.

There was nothing that needed to be done to make it work. Maybe some exhaust particularly at high loads would blow out that equalization line, but so what, no harm.

So think about plumbing it this way overboard and eliminate the solenoid valve.

David

Nice fix. No active components to fail.
I can tell you from my nuclear power plant experience that solenoid valves and seawater are VERY maintenance needy to work reliably, even the stainless steel nuclear grade $$$$$ ones.

 

[Paul Swanson]

Paul:

I hate to rely on something electrical/mechanical for safety on a boat. On our long gone Mainship 34T there was an equalization line (for lack of a better term) from the bottom of the lift muffler to a thruhull below the water line. That line, about 3/4" in diameter assured that the water level in the lift muffler could never get above the outside waterline. That left the water about 6" below the turbo inlet, so it was safe.

There was nothing that needed to be done to make it work. Maybe some exhaust particularly at high loads would blow out that equalization line, but so what, no harm.

So think about plumbing it this way overboard and eliminate the solenoid valve.

David

David,
Nice idea for your Mainship but my muffler is mostly below the waterline, hence the possibility of siphoning into the muffler through th raw water inlet.

Paul

 

[2ndlaunch]

Worried about drowning my engine 6BT Pacific Trawler

There have been some 40 ft. Pacific Trawlers with 5.9 liter Cummings engines that have experienced engine damage from water entering through the turbocharger into the cylinders. I looked carefully at my own installation and determined that the external water line was only inches below the turbo and inlet to the exhaust manifold. Furthermore, the static water level in the water lift muffler after shutdown was less than one ft. below the turbo. According to most experts the turbo should be considerably higher than this to provide a fail-safe exhaust system. I was quoted about $2500 for the S/S plumbing to raise the turbo on my boat.

I decided on a completely different approach which consists of a drain hose connected to the bottom of the water lift muffler and a simple normally open solenoid controlled valve connected to the “ignition” switch. When the engine is started the valve closes and the exhaust operates normally. When the engine is stopped the solenoid opens the valve and the water drains out of the muffler into the bilge and is carried overboard by the bilge pump. Any water that should enter the exhaust system inadvertently simply drains into the bilge. I can find no weakness in this system and the total cost was less than $50.

Paul

Hi Paul, I have a (new to me) 2001 Pacific Trawler 40 with 6BT and the same worries. Would like to implement your solution with the solenoid. Will you post or send me the specs on this solenoid and accessories you installed?

My exhaust run totals about 24' from the lift muffler to stern! 8' run from the muffler to a "small" rise beneath the kitchen sink and turns then with a very gradual fall 16' to the exit witch is 1/3 submerged. The small rise spillover is only 7" above the waterline. We do have a surge chamber, but with 16' of 6' exhaust that holds water we need to cut into and add 7" or 8" more inches to that riser (spillover point) We will be using a Centek 6" 180 return to accomplish this. I do have a flap valve covering the exhaust and also have an experimental 6" duck bill (low crack pressure) valve in my tool box ready to try out later.

My boat also has the low mixing elbow as yours does and I was missing the anti siphon valve in the raw water line above and before its injection point to the mixing elbow. That will be corrected. I would like to use your solenoid controlled muffler drain idea. I have been draining mine manually and leaving a note to myself on the dash to remind me to close it before starting.

We are loading (heavy) the boat to start an extended cruise this fall. Weight and balance is thrown off by the 3' factory extension to the boat that added buoyancy to the stern without compensating elsewhere. Our boat (and exhaust) was sitting bow down. I added lead in the stern to partially correct this and i do now know what our loaded waterline will truly be.
Thanks,

 

[psneeld]

How about a manual valve on the muffler drain with a warning buzzer if the engine is on and the drain valve is open?

Not automatic, but it won't fail at an inconvenient time like a solenoid might.

I am redoing my mufflers right now because I am replacing exhaust hoses and I bought the correct water injection elbow for my Lehman.

The water injection there is only a couple inches below the output of the exhaust manifold. And only a few inches above the waterline. So I made an anti siphon loop...like experts put in the books.

But I couldn't get the muffler low enough to be 12 inches lower. I could only get it 4 inches lower.

I called Vernalift and the tech said while not great, as long as the run from the elbow was all downhill, and the volume of water from the vertical portions between the manifold and the fall to the transom contained less water than the muffler could hold...I should be alright.

Some of those distances are for extremes of sailboat heeling. And the vertical distances to reduce back pressure.

So before worrying too much....see if some slight changes might bring everything back into the comfort zone. Yes I was told to put a fancy riser in the exhaust too...but my setup worked fine for 28 years where the muffler was actually the same level with a 2 foot flat run to it. The muffler tech was really suprised it all worked for so long...but it did.

I figured that making it slightly better, recalculating and accurately measuring all the new levels, reconfirming volume issues would make me feel better about reducing the chances of water in the engine.

If it were a brand new install, yeah, $2500 for a custom riser might be in the budget along with any other necessary mods to make it "perfect".

"Time tested" is hard to argue with though.