Epoxy water lock for wet exhaust

Does your current picture lack the waterlock? Or is the muffler the waterlock?

 

Now that you mention it I'm not sure what the term water lock means. Anyway in this present design the muffler is supposed to accept the wet exhaust, spray it around inside the muffler chamber (hopefully in such a way to minimise hot spots) then expel water and exhaust gases from the lowest point. From all the water lift designs one sees I 'm thinking the pressure of exhaust is enough to lift the water up, along the hose and over the gooseneck.

Hmmm - that's a head of water of about two feet - 600 mm. The back pressure generated by a 600 mm lift is about 0.9 psi or 6 kPa (15 psi x 2 feet/33 feet = 0.9 psi)

Checked Yanmar specs - the max exhaust back pressure is 30 kPa - five times more than the 6 kPa water lift pressure. So if the 3 inch hoses don't cause too much back pressure this water lift system should be OK. It would be good to somehow have baffles that could be adjusted to optimise noise reduction.

Now I just have to decide high temp resin or stainless - stainless seems safer

 

Straight up from the muffler, over the loop and out the side would eliminate the belly in the line to the transom. (Per your drawing).
I found a couple of simple drawings, I prefer the second illustration where the dry exhaust riser takes the hot gasses above the waterline, and only injects water where gravity will positively pull it away from the motor, and it cannot flood the motor unless the boat sinks!
Ideally, the dry loop would be higher than the hull exit.
A muffler drain is good to have, for emergencies and for winterizing. It could be plumbed directly to a small diaphragm pump, but would need a valve too, perhaps remote operated?

 

Not sure if phenolic resin is high temp. It is fireproof in the sense that when it burns, it forms a soot which is a very effective heat insulator. It is used in rocket nozzle.

We used high temp epoxy just to be safe. When you touch the tube while engine is running, it is warm, not hot. Well, we did on one occasion, the water pump failed and the tube was smoking but no fire. It cooked the high temp rubber hose.

 

overheat alarm should have gone off?

 

@kapnD_ Nice illustration. Yes I remember there is a vent tube. That is to prevent vacuum lock. To prevent the engine (when it cools down) from suctioning the residual water into the engine block. It is very important.

Attached typical cross section of waterlock.

 

The engine is not overheating. There was a separate pump for water spray. The waterpump is for dedicated engine cooling system.

 

Allow me to be the idiot here.

So, what is the volume of water in the system from the gooseneck to the muffler?

isn't the lowpoint in the long hose run the (effective) waterlock?

What is the volume of water in the muffler? Can the muffler take all the volume of water from the gooseneck back to the muffler, plus the muffler's contents and not overfill back to engine..

it seems some calculations of volume are also needed?

 

The water pump failed and the engine did not overheat? I am confused, but also the idiot. Just seems like alarms would occur if seaweed blocks intakes as OP mentioned or if water pumps fail.

 

When you shut off the engine, the water spray stops and there will be some water in the system. Also the water in the exhaust tube is no longer pushed out and will drain back into the waterlock. Thus you have enough water to fill up the waterlock. Even if the waterlock is not filled to capacity, the vacuum (cooling down effect) will suck the water in the waterlock flooding the engine, hence the vent tube or vacuum valve.

I wish I could find the Volvo Penta technical publication I used to have. It has been a long time.

 

Maybe Michael is just confused over the difference between a wet muffler and waterlock. Here is the configuration.

 

Phew - a lot of thoughts

OK I get the meaning of waterlock from your second sketch - thanks rxcomposite - water lock and water lift seem to be the same concept
I am trying to make a custom water low profile water lock exhaust system

Stepping back a bit let's define the water lift problem

1. Yanmar want the water in the muffler to be 250 mm below the exhaust elbow
2. The water left in the exhaust hose must not get back into engine
3. Therefore some sort of bucket/muffler/water lock must be below the hose and accept all the left over water when the engine is cut
4. The conventional Vetus muffler (thanks rxcomposite) is too tall - it will not satisfy the 250 mm rule - the engine is too low in the hull
5. Yanmar also require the gooseneck at the aft end and it must be 350 mm above water line - so seas don't wash in

While I could ignore Yanmar's rules it would be wiser to accept that they might know a thing or two

So two solutions

1. A Yanmar high lift water cooled exhaust elbow and the Vetus muffler - (high lift elbow kit is about $1,000, Vetus water lift muffler about $600?) or

or

1. Keep existing Yanmar mixing elbow - I like it - it's pretty clever - two concentric tubes - water in the outer one - no heat
2. Make a low profile water lock vessel 250 mm below the existing water cooled mixing elbow
3. This water lock must have a volume at least 16 litres so the hose (max 8 litres) doesn't flood it and deliver water to the exhaust manifold - (fallguy's concerns)
4. A vent tube that empties the muffler when engine stops (idea - a small diameter inverted U tube - U high above water line - that flows a fraction of the exhaust water from bottom of muffler when engine running - and continues to siphon empty out above water line when engine stops - acts as vacuum breaker as engine cools)
5. A temperature sensor on the mixing elbow in case the impeller fails and water stops

Do we have a consensus?

 

While we wait for the concensus, you might want to visit this thread. Water lock pressure loss calculation https://www.boatdesign.net/threads/water-lock-pressure-loss-calculation.43308/

You can also google images of Vetus and Volvo Penta waterlock design. Vetus and Volvo have low profile ones to base your fabrication on. volvo penta waterlock design

The elbow is not a hard and fast rule. It is to keep the waves from entering the system, thus it is the height from the waterline to the top of the elbow that matters. A flapper valve can help mitigate this.

 

While you can get away with a minimum of 1 baffle, 2 is standard. 3 for the more compact but complicated design.

 

You can buy these cheap from any marine catalouge. Try West Marine, Port Supply or any similar catalouges. It is vacuum controlled. It wont empty the waterlock but prevent vacuum from forming.