When do you need a waterlock muffler?

[sailingunity]

My exhaust is set up such that the muffler directly behind and is roughly 12" below the exhaust manifold, then the hose comes out of the top of the muffler and drops down to the floor (to roughly the same level as the bottom of the muffler), runs that way for about 8 feet or so and then starts to climb to the outlet with 2 90's in a "U" configuration before exiting the boat.

All the documentation I've read makes it sound like you MUST have some kind of a waterlock to catch all of the water in the hose when you kill the engine. Otherwise you risk backing up water into the manifold, especially if you need to crank longer than normal to start. The way I see it though, the roughly 8 feet of hose that is at the lowest point is a waterlock of sorts, after all while the engine is running you have exhaust gases passing through it so 100% of the volume not water. When the engine stops any water left in the hose would fill in the low area.

Is my logic right? I'm actually re-routing my exhaust from the port side to the stern and it will turn out to be basically the same length as before - just wanting to double check with the community here if I should consider adding a waterlock when I do it.

[zboss]

What happens when your stern lifts and you bow dives?

[sailingunity]

I suppose there is some degree of sloshing going on inside the hose, your point?

[model 10]

Unless you have a water lift to blast out the load of water that's in the hose and the water lift, you will have water above the engine. You get how a water lift works right? A hose could not be a water lift.

[sailingunity]

Well I should be more specific in that the muffler directly behind the engine is a water lift muffler.

[CassidyNZ]

Originally Posted by sailingunity

My exhaust is set up such that the muffler directly behind and is roughly 12" below the exhaust manifold, then the hose comes out of the top of the muffler and drops down to the floor (to roughly the same level as the bottom of the muffler), runs that way for about 8 feet or so and then starts to climb to the outlet with 2 90's in a "U" configuration before exiting the boat.

The way you have described this would indicate that the installation isn’t totally correct. The muffler/waterlift should be the last component in the system that literally blows the water out of the boat. It should be (and seems it is) installed below the level of the mixing elbow but the exhaust system should not then wander around at a level below the waterlift. The waterlift should be able to easily accommodate all the water left in the rising part of the exhaust when the engine is stopped.

To give an example:

I have just finished working with a Yanmar agent on a new 4JH4-TE repower, commissioned on Last Friday. The waterlift is right alongside the engine and below the level of the exhaust mixer. From there the exhaust rises consistently over about 6ft to a high point and from there it falls consistently over about 9ft to the skin fitting in the transom.

On my own boat (also Yanmar 4JH4E) a 100mm rubber pipe runs from the exhaust mixer down to the floor of the engine room, about 7ft alongside the engine to in front of the engine. From there into a waterlift and another 100mm rubber pipe runs from the top of said waterlift up to the roof of the engine room (3, maybe 4ft) then down to the side of the boat where a skin fitting vents into the water. The whole up/down section after the waterlift is probably 7ft long.

Hope all of this makes sense

[sailingunity]

Thanks for the detailed description of your waterlift muffler arrangement. Since I have a center cockpit boat my options are slightly different, but I could put the waterlift under the floor in the aft cabin, which would be the lowest point, which would then rise to the stern, I suspect the rise would be more than 6 feet though. My exhaust hose is 60mm.

[zboss]

Originally Posted by CassidyNZ

The way you have described this would indicate that the installation isn’t totally correct.

I agree, the general rule is that the exhaust line after the waterlock should immediately rise to some distance (at least 20 inches above heeled waterline for my beta) and then gradually slope down towards the exhaust port before exiting. There should not be an upwards slope anywhere in the line after the initial rise.

However, the contention that the waterlock should be the last component is incorrect, it should be at least 1 foot vertically and 1 foot horizontally but that distance should be as short as possible from the engine to minimize the amount of water between the engine exhaust riser and the waterlock muffler. The waterlock pressurizes from the exhaust gases and pumps the water up over the subsequent rise.

The exception to the above is if you are using a gooseneck in addition to the waterlock, where the gooseneck would be the last component, or if you are ONLY using a gooseneck.

[JOHNMARDALL]

In most wet exhaust systems, a goose-neck/swan-neck/ etc. (select your national long-necked water fowl) will be installed at the transom, tight under the deck and providing a high point to prevent flooding from a wave or wake breaking over the stern of the boat. The high point can be created by taking the exhaust hose up to the deck before it drops to the transom outlet.
On engine shut down. the water in the exhaust hose, from the high point to the engine, will drain back toward the engine and must be prevented from flowing through the mixing elbow. into the exhaust manifold, and into a cylinder through an open exhaust valve. A water lock is.at its most simple, a sealed bucket with enough volume to hold all of that flow-back water so that it doesn't reach the mixing elbow. It follows that the entire volume of the water lock must be below the mixing elbow, and that the water lock and the top of the goose-neck should be on the center line of the boat to ensure that they're not over-topped when the boat is heeled.
To determine the minimum volume of the water lock, calculate the internal volume of the exhaust hose from the top of the goose-neck to the bottom of the water-lock and assume that 25% of that volume is water (the remainder being exhaust gas), then double that volume to allow for the possibility that the water lock will already contain water on shutdown


Don't forget that you must also protect the engine against flooding from the raw-water intake side by installing a siphon-breaking air vent/vented loop/vacuum breaker, etc. (your choice of short-necked water fowl?) between the heat-exchanger and the mixing elbow injection port.


If you'd like to email me direct at jmardall@comcast.net, I'll send you some slides from our exhaust system training module.


Good luck and be careful - getting this wrong will destroy your engine.


John Mardall
Vetus Maxwell Boat Equipment

[model 10]

Think about venting the top of the vacuum break into the cockpit or ovbd. A small 1/4" hose going somewhere, instead of the silly little rubber valve that clogs up and does not work.
I have mine going ovbd right next to where I sit in the cockpit. I'm surprised at how little water comes out the little thru hull. At low cruise, nothing. At normal cruise there is a small flow that you can touch and feel the water temp. I also like the instant input on the water pump status.

[sailingunity]

Yes we have a vacuum break in our system already, before the injection point, so we are covered there. Due to the engine room being in the middle of the boat it just drains into the bilge, but I could possibly re-route it to drain through one of the cockpit scupper drain hoses also located in the engine room.

I emailed you John!

[JOHNMARDALL]

Originally Posted by Ecos

Think about venting the top of the vacuum break into the cockpit or ovbd. A small 1/4" hose going somewhere, instead of the silly little rubber valve that clogs up and does not work.
I have mine going ovbd right next to where I sit in the cockpit. I'm surprised at how little water comes out the little thru hull. At low cruise, nothing. At normal cruise there is a small flow that you can touch and feel the water temp. I also like the instant input on the water pump status.

That's exactly how we have it set up in our own boat, but some boat builders and some boat owners prefer the internally vented vent with the rubber (silicone) duck-bill valve because they don't want the external breather fitting.
That's why we offer both - some people like vanilla and some people like chocolate.and can prove that their choice is the best.
All the best
John Mardall
Vetus Maxwell Boat Equipment

[CassidyNZ]

Originally Posted by sailingunity

Thanks for the detailed description of your waterlift muffler arrangement. Since I have a center cockpit boat my options are slightly different, but I could put the waterlift under the floor in the aft cabin, which would be the lowest point, which would then rise to the stern, I suspect the rise would be more than 6 feet though. My exhaust hose is 60mm.

Actually my boat is also a centre cockpit but I’m lucky to have quite a big (almost walk-in) engine room. The engine is mounted towards the aft end of the room so the waterlift needed to be mounted at the front of the engine and on my boat, also ahead of two big-frame alternators that are fitted to the engine. So the pipe from the mixer to the waterlift runs alongside the engine to the waterlift and as I mentioned, is about 7ft long. But it runs at a downward slope so the water in the pipe at shutdown time empties into the water lift.

My exhaust, in contrast to ultra, exits midships directly abeam of the waterlift and all of this is within the engine room.

[CassidyNZ]

Originally Posted by zboss

However, the contention that the waterlock should be the last component is incorrect, it should be at least 1 foot vertically and 1 foot horizontally but that distance should be as short as possible from the engine to minimize the amount of water between the engine exhaust riser and the waterlock muffler. The waterlock pressurizes from the exhaust gases and pumps the water up over the subsequent rise.

Why I said “the last component” is to point out that there shouldn’t be an array of bends, dips and long pipes after the waterlift. The waterlift should have only the pipe that takes the water out of the boat. I suspect, although not said, that you concur.

Also, within reason there is no critical need to minimise the volume of water between the engine and the waterlift as long as the waterlift has sufficient volume to safely gather all the water coming at it from both sides when the engine shuts down. As I mentioned in my first post, the pipe between my exhaust riser and the waterlift is about 7ft, considerably more that 1ft. The water from the inlet pipe and the outlet pipe both empty into the waterlift when the engine stops.

[sailingunity]

Originally Posted by CassidyNZ

Actually my boat is also a centre cockpit but I’m lucky to have quite a big (almost walk-in) engine room. The engine is mounted towards the aft end of the room so the waterlift needed to be mounted at the front of the engine and on my boat, also ahead of two big-frame alternators that are fitted to the engine. So the pipe from the mixer to the waterlift runs alongside the engine to the waterlift and as I mentioned, is about 7ft long. But it runs at a downward slope so the water in the pipe at shutdown time empties into the water lift.

My exhaust, in contrast to ultra, exits midships directly abeam of the waterlift and all of this is within the engine room.

My boat has a walk in engine room as well, but flanked on both sides by cabin space which is why the exhaust hose has to dip back down to go under the floor. Our exhaust originally exited right at the waterline, the previous owner actually relocated the exhaust higher on the side for fear of the fitting below the waterline springing a leak. I don't blame him for doing this, but now we get a lot of "overspray" in the cockpit anytime the wind is coming from the port side (I know, we should be sailing) this is the main reason I'm relocating it.

From the waterlift, it runs roughly 9 feet below the floor before rising about 4 feet to the gooseneck. Image attached with the ideal new route.