Deviation from Standard Installation of Wet Exhaust

[Night Watch]

1977 Catalina 30', Atomic 4 engine: I'm replacing the engine, so I have the stove and kitchen bar removed currently. I'm also replacing the Aqua Lift Muffler and why not replace the exhaust hose, right? So, I was evaluating the exhaust hose replacement project and come to find out my exhaust hose is 100% "inside" the cabin space. No part of it enters the port side lazarette. At the ice box it turns 90 degrees and parallels the gas tank heading to the transom. Also, the one-way check valve is not there.

Q: Should I install the new hose according to Catalina production schematic run? I'm thinking it would be beneficial to do so to better prevent inflow of seawater during following seas or a port tac.

 

[Ralph Johnstone]

Also, the one-way check valve is not there.

Q: Should I install the new hose according to Catalina production schematic run?

Does the original Cat installation employ an internal loop which rises as high as possible to avoid seawater backflow as opposed to using a check valve. The internal loop is the most common method I've seen of avoiding backflow.

 

[Night Watch]

No it does not. the production route comes out of the aqua lift muffler rises about 18 inches, goes behind the stove and ice box up another 6 inches and out into the port lazarette where a one-way valve would be installed. These one-way valves were prone to failure, and at the point where this would be is directly under the lid of the port side lazarette, pretty high off the water. At this point the route dives back down to the aft bulkhead at the waterline and through it to the transom through hull

 

[Night Watch]

I've been reviewing photos of other members exhaust hose replacement jobs, and I have a question:
It appears some 30' boats (talking about Catalina 30's only) hoses run "over the top" of the aft bulkhead of the port lazarette and others run through this aft bulkhead at the bottom. So far it's my opinion that the higher the better, especially if there's to be no loop or one-way check valve.

 

[Ralph Johnstone]

Don't know what those Cat guys were smoking when they came up with that exhaust system :

................ but in order to have backflow due to a following wave, you would need a wave higher than your lazarette = H. A check valve any where in an exhaust hose is not recommended because the corrosive exhaust gasses would eventually corrode out the flapper or the flapper would plug with carbon.

If the exhaust hose lays on the bottom of the hull as mine does, then you need an exhaust loop. In my H-310, the exhaust hose lays on the bottom of the hull from the engine exhaust all the way back to where the bottom of the transom meets the bottom of the hull :

When it reaches the bottom of the transom, it rises up in a tight loop to the height of the transom and then down to the bottom of the hull where it discharges underwater.

Backflow is only possible if a following wave rises to the top of the transom with the engine shut down. At that point, one would have far greater problems than backflowing water in the exhaust hose .