Volvo Penta Exhaust setup question

[mattonthesea]

I recently posted about my exhaust muffler leaking. Thanks for the replies which have led me to think that I need a waterlock. In the meantime I have realised that why the system is set up as it is. At the moment the exhaust pipe comes from the elbow and makes a downward and forward run under the engine. It then loops up and along the side of it just below the level of the elbow. It drops slightly and then runs up, under the cockpit to the highest point by the transom where it turns down and out through the transom. I estimate that about 2-3 m is below the level of the elbow and about 1.5-2 m is above it. Assuming 25% of the volume is water then the 'above water volume is about 0.75 l and the the below elbow volume is about 1.5 l. The total volume below the elbow is about 5 l. Therefore, the total volume of water left in the pipe is about 2.25 l and it has about 5 l of pipe to sit in.

I assume that this is the reasoning behind the setup. I am also assuming it was done this way because there is very little room behind the engine and below the elbow to fit a waterlock in.

Any thoughts?

Thanks

 

[mattonthesea]

So my next question is about how to position a watertrap. The lowest I could easily (not ridiculously hard) place it is about 500 mm behind elbow and slightly higher (100mm) . That would be about 200ml of water to flow back; is this too much?

 

[duncan99210]

The Vetus installation manual has a series of drawing showing how to position the various elements of an exhaust system. Link is here https://www.vetus.com/media/magentominds/sasdocument/20200615094047_0.pdf , with layout diagrams at page 15 onwards. Have a look at the drawings and decide which best fits your boat layout.
One question: you refer to a muffler and the need to fit a water trap as well. If the muffler is the usual VP one, it combines both functions and you can simply fit a Vetus plastic one in its place.

 

[VicS]

So my next question is about how to position a watertrap. The lowest I could easily (not ridiculously hard) place it is about 500 mm behind elbow and slightly higher (100mm) . That would be about 200ml of water to flow back; is this too much?

The water trap should be behind and below the outlet from the elbow.

There are some diagrams and a formula for calculating the required volume of the trap from the dimensions of the exhaust hose in the Vetus on line catalogue. I think the diagrams are the same as those in the installation instructions.
The object of the trap is to contain all the water left in the hose when the engine is stopped. The formula assumes that the hose is 25% full of water but includes a X2 safety factor.

VETUS Catalogue 2019 - 2020 - English

I guess the routing of your hose is because its impossible to position a trap behind and below the elbow.