Engine exhaust systems

[JonnyBoats]

I am changing out the exhaust hose in my LeComte Northeast 38, which causes me to wonder what the "ideal" exhaust system would be?

I ran across this article http://www.docksidereports.com/sail_boa ... iaries.htm where the author states:

exhaust riser failure is the number one cause of major engine damage

and

excessive exhaust system back pressure caused by creating risers that are too high

.

Further he goes on to say

If you?ve got one of those exhaust systems that pushes water up three feet before pushing out the exit port, you should seriously consider having your exhaust system redesigned, for the ultimate benefit of increased engine life will likely be well worth the cost.

Since putting a high loop in the exaust after the muffler is common, often with a small radius U shaped fitting or syphon break at the top, this advise seems to go against common practice.

What would be the "ideal" exaust system be if one were designing a new installation and there was sufficent room (often not there on older boats) for what was best?

[Figment]

The internet is a wonderful and dangerous thing sometimes. That article is interesting, though it does suffer from a bit of tunnel-vision. The author seems to evaluate the exhaust system solely on the basis of engine longevity and efficiency, without acknowleging that a few other whole-boat influences need be considered as well.

Those high-loop exhaust risers don't exist in sailboats because they're fun. (They're not fun. At all.) They exist because sailboats don't always stand up straight, and because seawater is just such bugger sometimes!

Of course it's a good idea to have an air filter, but who has the space, and really how many engines have died before their time because they inhaled too many particulates?

On your last question regarding the "ideal" setup, I think that Vetus have diagrammed it out very well. The parameters they establish are not always achievable in old boats, but you can't fault the clarity of the information.

(this is all just one sailor's opinion, of course)

[bcooke]

What Mikes says.

I subscribe to several magazines but I get them mostly for the pictures and ads. I find when I read a published article about something I am already knowledgeable about, I usually walk away muttering about the nonsense that gets passed around as 'expert knowledge' these days. This makes me really wonder about the stuff I don't know about that I read in the magazines. I think much of the time the writer gets their info by interviewing an 'expert' or two and a lot gets filtered out or some serious bias gets thrown in during the process. Sometimes I even wonder if the writer is just making it up to earn a quick paycheck (small and inferior though it must be) I think the Internet is exactly the same as traditional print except it is so much easier to 'publish' that even more rubbish gets disseminated.

As for your exhaust, your engine is operating in a fairly hostile environment so I think making it perfectly safe and happy is probably not going to happen. I think following the manufacturer's recomendations is probably as safe a bet as any. I am guessing but I would think any operating manual will have some basic guidelines for installing the exhaust system - which is NOT part of the engine as far as the manufacturer is concerned.

Some fairly respected books like Nigel Calder's Boatowners Maintenance and Electrical Manual probably has some good ideas too.

-Britton

[Tim]

Here's the basic ideal for a wet exhaust, in my opinion. Of course the actual spaces in question will usually force some other sort of configuration, but there you have it.

1. Stock engine riser with cooling water injection on the downslope

2. Large waterlift installed lower than the exhaust manifold outlet as much as practicable

3. Exhaust hose arched as high as possible directly at the transom outlet. In most sailboats, this is limited to a couple feet or so, and often less.

4. Ideally, the exhaust outlet would be in the transom and high above the water. This would minimize or virtually eliminate any chance for the outlet to ever become submerged. If the outlet's never submerged, all worries about backflow and siphoning cease to exist.

Of course, aesthetic concerns usually dictate placing the outlet in the counter somewhere, or lower in the transom. But even though this causes the outlet to submerge under some sailing conditions, true problems arising from water backflow are rare. The high loop pretty much takes care of this.

[JonnyBoats]

Since we are talking about "ideal", how about:

1) Maknig sure the exhaust manafold is well above the water line.

2) Putting the exaust exit somewhere easy to see from the cockpit.
Everyone I know checks for cooling water flow when they start the engine, and with some cockpits and outflows hidden under the counter, this can involve some serious gymnastics.

[Tim]

Since we are talking about "ideal", how about:

1) Maknig sure the exhaust manafold is well above the water line.

Well, the manifold will either be above or below the waterline, and there isn't much one can do to change this. Many small sailboats' engines, particularly in older-style boats with deeper bilges, end up either right at or below the waterline. This is the reasoning behind the tall dry stacks seen in some installations--to effectively raise the manifold's exit point, depending on other factors of the installation. On my diesel, the top of the stock exhaust riser is a couple inches above, the waterline. This is one reason why I saw no need for any sort of taller stack. Other installations may have the outlet so far below the waterline that some sort of built-up riser is required.

Ideally, the riser extends above the waterline. But we know that it's not always possible, and some older engines don't really have a riser; the manifold exits horizontally, or even lower than that. It's nice to have an ideal to shoot for, of course, but practical limitations tend to get in the way. I think that other components of the exhaust system will combine to dictate how critical, or how tall, a riser is.

Old-style jacketed exhausts were probably far more susceptible to these backflow concerns, as they didn't incorporate much in the way of backflow protection at all. But newer waterlift exhausts are much safer in this regard.

2) Putting the exaust exit somewhere easy to see from the cockpit.
Everyone I know checks for cooling water flow when they start the engine, and with some cockpits and outflows hidden under the counter, this can involve some serious gymnastics.

4. Ideally, the exhaust outlet would be in the transom and high above the water.

This ideal location would take care of the desire for an easily-viewed location. But all installations aren't ideal, of course. Such is the nature of boats. So we crane our necks over the side to see it wherever it may be. Sailboats are rarely ideal...

Most diesels pump enough cooling water that it's pretty easy to hear the splash as it hits the water, often a foot or more beneath the outlet. I know I can tell instantly if there's no cooling water just by the note of the exhaust. But I always make a visual check too.

[JonnyBoats]

OK, since this is "boat nerdery"

Leaving ascetics aside (after all, from a traditional point of view a sailboat wouldn't have an engine), why should the exhaust exit through the stern?

On a Coast Guard 47 ft motor life boat the exhaust exits through the sides just ahead of the stern. There is an exit on each side. There are twin engines and the exhaust runs are crossed so that the engines can continue to run even if the boat is rolled through 90 degrees.

On a traditional sailboat with a bridge deck and the waterlift muffler roughly under the bridge deck (or slightly aft), why not run the exhaust hose straight up from the muffler to a T fitting? Then from the T run hoses awartship from the T to thruhulls on the port and starboard sides exiting the sides just under the bridge deck.

With this setup, if the boat heeled enough to put one of the thruhulls under water the other would be well clear on the high side. The only time both could be underwater at the same time is when the boat is on the verge of sinking.

Has anyone ever heard of this being tried on a sailboat?

[Tim]

Exhaust odor and smoke, not to mention the potential discoloration/staining of the hull on the topsides in a highly visible area, tend to be among the practical reasons why you don't see exhausts located the way you suggest.

...(after all, from a traditional point of view a sailboat wouldn't have an engine)...

Perhaps. Yet most sailboats do, and therefore must deal appropriately with the practical aspects of their installation--including, necessarily, the aesthetic concerns (which are not limited to only visual--this includes other tangible senses as well).

Note also that powerboats, with engines running continually, don't suffer from these backflow concerns in the same way since the exhaust pressure prevents water from running inward through the outlets. It's even typical these days for many powerboats to have their exhaust outlets completely underwater to muffle the sound and reduce odor.

...ascetics...

What do monks have to do with this discussion on aesthetics? ;<)

[Figment]

I know of one sailboat with the exhaust high on the topsides.
It's an Evelyn 25.5, which has the engine located forward, atop the keel. The shortest exhaust route is to the portside, so that's what he did. When motoring, he fits a +/-8" length of plastic pipe into the outlet (which is otherwise completely flush and fair, invisible from 15' away) to eject everything down and away from the topsides.

It's actually a very nice solution for a boat that really only uses the motor to zip out to the racecourse.

[Rachel]

Perhaps "Der Alte" will chime in here, since it's his boat, but I think the (some?) Westsail 32 has an exhaust outlet on each side of the (canoe-sterned) transom.

We were once traveling in tandem with a Morgan 30 in some rough weather and they experienced engine trouble due to their single exhaust being underwater much of the time, whereas we had no trouble that day. It was real "bucking bronco" conditions though, nothing you'd normally expect to experience.

I thought this was called a "North Sea" exhaust; that being said, a quick "Googling" didn't back me up.

[Tim]

The classic Tartan 30, which has its engine mounted way forward just aft of the mast, has an exhaust outlet about amidships, and just a little above the waterline.

I'm not sure of the details of the remainder of the exhaust setup in this case, though.

[Figment]

Tartan 30!!! Thank you!

I knew there was a well-known benchmark cruiser with this arrangement, but I just couldn't crystallize it in my mind. That was going to drive me nuts all day.

[fusto]

The Sparkman and Stephens Yankee 30 also has midships exhaust.
The muffler runs up the bulkhead in the head!