Engine exhaust

The engine is installed with the original exhaust system, but part of it has rusted out, so I need to decide how to proceed. I can fix the existing system or replace it, and if replacing I can redesign in a variety of ways.

The existing system takes the exhaust from the back of the engine and routes it forward, under the exhaust manifold (since the replacement diesel doesn’t have the option of exiting the exhaust from the front of the manifold like the original Atomic IV did), and up to the exhaust cooling stack in the head. This device is quite clever – it consists of two concentric tubes, the inner one for exhaust, the outer for cooling water. Both enter independently at the bottom of the stack and rise to the top where they exit together. The exhaust, however, has to rise considerably higher than the cooling water, and come back down. By the time it’s gotten there it has been cooled by the water it’s been surrounded by, and it joins the water which flows with gravity down the flexible pipe to the transom (along the port gunwale). This system, unlike the more common waterlock systems, cannot let cooling water back into the engine since it runs out of the boat with gravity and doesn’t rely on exhaust pressure to push it out of a waterlock. Engines have been known to get flooded from excessive turning over without starting with waterlock systems – although they obviously work pretty well.

If I put in a waterlock system I can either route the exhaust the same way it is currently routed – i.e. forward into the head, thence down the port gunwale, or I can route it through the bilge and up under the cockpit in the more conventional fashion.

As I write this I’m undecided between fixing the existing system and replacing with a waterlock, routed through the bilge and under the cockpit. I don’t think I’d route a waterlock system through the head. But this is early in the decision process, who knows?

I just came across some information which makes me lean toward a waterlock: Rod Stephens, in his unfinished book mentions convincing a client who is building a second boat from the same design he built his first from to use a waterlock instead of the original standpipe waterjacket. Here’s the quote:

And so he sold Kay and and the second boat was built. I asked Arnie what he was going to change on the second boat. He said “Nothing.” I said, “Well, there’s one thing I want you to do.” We had come into this new water lift exhaust system which was more durable, cooler and quieter that the normal system that we used to do where we build a standpipe water jacket to a high point and that did not have such a long life and was heavy and the new system was much better. Arnie was reluctant but he accepted this change and that was the only thing that was different in the second boat. The new boat was just as tight as the original and never leaked anywhere and the finish was beautiful so Walsted must take a front row in the highest quality of wooden boatbuilding in that period.

Update: I just discovered the comments people had left! Turns out I had to check if there were any and then approve them – but there doesn’t seem to be a way to have it notify me when they’re there, so I’ll have to check religiously. So it goes.

No pictures yet – the boat’s still full of sails and gear until the shed is done.

I like the sounds of your system, Owen, and especially like the fact that it has a very high loop in the head – that’s a good reason for sticking with the original routing of the exhaust rather than running it back out under the cockpit. I wouldn’t be able to have such a high loop off the manifold since my boat has a seat over the engine (at least so far), but as long as I’m convinced that the muffler has sufficient capacity to hold as much cooling water as I might push through while starting, that should be alright. My last boat had a high riser after the manifold before the water was injected, and I had a steady stream of trouble keeping it together – the engine vibration would break the pipe off at the manifold, time after time.

Here’s an image of Peter Jones’ waterlock in place in Emerald with no riser:

This seems to be a fairly common retrofit, and will probably be what I go with – with a high loop in the head – if the standpipe turns out to be unusable or I decide that having hot exhaust from the back of the engine up to the front is more than I can handle.

Further Update: I’ve taken the exhaust from the manifold to the pipe which exits the head out. This includes the mixing elbow and the standpipe (the more formal term for the cooling stack I mentioned above), as seen here:

I have to say that I have no idea how the motor ever ran with the existing system. The mixing elbow was the lowest point in the entire system, and the water and exhaust travelled together uphill to the standpipe, then vertically about 4’ to the top of the standpipe, then down and out. Maybe it didn’t ever work and that was part of the reason this boat sat idle for so long? The motor flooded and they didn’t know what to do? Who knows. I don’t – but the motor turns over, and I’m told it starts (remains to be seen, of course).

As can be seen in the picture, the connection to the manifold (don’t know the term for that part) and the mixing elbow are pretty badly rusted – especially the part that connects to the manifold. Of course I replaced that part on my last boat (identical engine) and it cost $300! Nuts. I’ll try sandblasting them before replacing them, but they don’t look good.

Back to how to reconnect the system. Turns out that the standpipe is intact – I managed to fill it with water from the bottom and it came out the top where it’s supposed to, and didn’t leak down the middle, where it’s not supposed to go. So reusing it is an option, which is nice. Trouble with it is that it would mean routing the hot exhaust from the manifold to the bottom of the standpipe – involving three elbows and a couple of feet of pipe – and connecting it there. The diesel engine, even a 4 cylinder, is not something which runs without moving – they rattle around quite a bit. So this connection needs to be flexible, but able to take the heat. It also needs to not fall apart from vibration, which it surely would if it had a 2’ section of pipe to support on the first two elbows, and then a piece of flex hose. So it probably needs the flex pipe nearer the manifold – where there isn’t really any room for it.

More and more it seems like I’m best off with a waterlock in the bilge, like Emerald’s system. But I think if I’m doing that I’ll get everything out of the head and the port gunwale and run it out the back of the bilge:

Under the aft dinette settee:

Under the galley sole and the stack of drawers to port:

And out through the port cockpit locker (where it already is, having arrived via the gunwale):

This means replacing everything – but the only part that I’ll have to buy that I don’t already is the waterlock, and I have a feeling that it’ll be cheaper and easier to deal with than the flex pipe I’d need to hook up the standpipe system.


Your thoughts?

  1. It would be helpful to see some photos or plans.

    John Tarbox · 12.01.09 · #

  2. Hello Beth & Chris

    I have a boat very similar to yours, a 1971 S&S30, built in the UK. I have owned her for a few years now, and one of the first things I tackled was the exhaust. A PO had totally messed up this upgrade. In fact, the day I went to sail the boat away I found the engine full of water; I later determined that this was due to an improper installation of a waterlift muffler. This boat still has the original gasoline Albin O-22 engine. The original design was a hot/dry ss exhaust pipe exiting from the rear of the engine and proceeding forward under the engine (DANGEROUS!) to the head compartment where was housed a standpipe as you describe. However in this boat the exit (which seems to make more sense to me) is right there in the starboard side of the hull. This had all been abandoned by the PO who had rigged a waterlift muffler under the cockpit (higher than the engine!!!) with the exhaust routed to transom. Very bad idea. My solution, which I spent many hours working out, uses the smallest Vetus waterlift which just fits in the bilge below the aft end of the engine (which in this boat resides under the saloon table). I have the exhaust riser from the engine go vertical far enough so that its highest point is above the waterline at all angles of heel. (I had to raise the dining table 3” to achieve this.) It then does a 180 deg downward turn at which point I reattached the old standpipe; here the cooling water is injected. The standpipe transitions into a short piece of rubber exhaust hose and to the Vetus directly below. The Vetus is oriented in the bilge to send the exhaust/water mix forward to that same void in the head compartment (that held the standpipe) where I have a very high loop which terminates at the original exhaust through-hull in the starboard topside. Neither loop is vented. This setup has worked perfectly for three years now. I hope my solution will provide you with some food for thought.

    Owen McCall · 5.02.09 · #

  3. A couple of things to keep in mind regarding your waterlift issue.

    If you open the raw water seacock and crank the engine enough, you will fill up the waterlift muffler and back fill up to the mixing elbow and if you keep cranking you will back fill one or more cylinders with sea water. So it is always possible to flood an engine in that way.

    The waterlift muffler must be large enough to hold all the water in the exhaust hose from the outlet of the waterlift to the thru-hull, otherwise that water will run backwards when the engine is shut down and flood the engine.

    Finally, it is not necessary that the exhaust riser be above the water level of the boat, it is only necessary that the siphon break be above the max heeled water level and the siphon break can be anywhere as long as it is plumbed into the hose that injects water into the mixing elbow.

    Good luck,


    David Browne · 19.08.09 · #

  4. Thanks, David – all good things to point out. That’s one thing that’s nice about the standpipe system – it eliminates the possibility of water running back into the engine. Pretty much the only way to get water in your engine with a standpipe system is to pressurize the exhaust run aft (with water) to the point where it pushes up and over the top of the standpipe – which is not really possible.

    The downside to the system is that it’s old, it’s heavy, it takes up room in the head which is already small, it requires a very long run of hose, and it requires a longer run of hard pipe with a section of flex.

    In other words, since the waterlift is a well-understood and reliable system when properly installed and used, the benefits of the standpipe fail to outweigh the costs.



    Chris Campbell · 19.08.09 · #