In-line wet exhaust check valve?

[captnjj]

I am in the process of installing a Jon Deere 4045 propulsion engine in my 25 foot fishing boat. It has a 4 inch wet exhaust 90° elbow that is angled about 20° downward in the direction of the stern. To matchup with the existing location of the in-line muffler, I am connecting a four-inch flexible 90° elbow, which I will connect a four-inch fiberglass tube that is about 5 feet long running from the port side location of the wet exhaust elbow to the starboard side of the boat and another 90° elbow that connects to the muffler that runs towards the stern and out the transom.

The drop from the wet exhaust elbow across to the starboard side elbow where it connects to the muffler has only about a 5 inch drop. From the exit of the muffler to the waterline is approximately another 10 inch drop.

The main concern is that the water in the section with only a 5 inch drop may wash back into the engine. I cannot raise the wet exhaust elbow, nor can I lower the muffler to create a larger drop.

I saw an in-line 4 inch check valve by a company that I think is called Centek, but I'm not sure if this is my solution or if there are other reasonable solutions without redesigning the entire boat.

Any professional thoughts about my options would greatly be appreciated. Thanks, Jon

[S/V Alchemy]

Well, it's not a professional thought, but you need to consider the geometry of this from all angles of heel under use to determine if it's sufficient. You also need to add an anti-siphon break or gooseneck or something past the mixing elbow, although that depends on whether you have any "uphill" to deal with (see here). A check valve in a plumbing setup...fine, but in an exhaust circuit? Gives me some concerns, frankly. On the other hand, Centek makes great stuff.

I think I would ask people with a similar boat and engine configuration what they do (and with pictures) and tally their results.