This is a test fit of some engine wet exhaust bits. Turns out the space planned for these, and the aft bilge pump anti-siphon loops (previously installed) was a bit too cramped. So, the pump anti-siphon loops had to be relocated. Turns out the new space for these has better access for maintenance anyway, so its all good.
I suspect most center-cockpit boats of this vintage had a similar limitation: where/how to run mechanical bits (exhaust, steering, etc) aft without interfering with the aft living spaces? I have seen some Westsail 42’s do a port side-exit amidships for engine exhaust, which can be a simple and easy install giving you the shortest hose run possible (ideal). But I can’t do that, given how I designed the engine room, without a big hose looming over your head. I would rather have exhaust discharge aft anyway.
So I came up with a stern discharge solution that involves a Vetus exhaust “gooseneck”. With wet exhaust you want the hose to “loop” up to a high point within the boat (the higher the better). This will prevent any following waves from “backfilling” into the exhaust and the engine. Saltwater backing into a diesel engine can kill it quickly unless you remedy it immediately (usually involves removing the engine heads before corrosion has a chance to work). If you have the space, simply looping the exhaust hose up-then-down from a high point is sufficient. But exhaust hose cannot bend enough for that to work in the small space we have.
So, this gooseneck provides the anti-backfill loop in a very compact space. I am somewhat loathe to use one of these. We tried one on a re-power of our small boat years ago. We removed it due to the excessive back pressure it created (exceeded the engine maker spec’s for warranty). But, after a lot of thought, this is really the only sensible solution for this project. To help with the back pressure, the size of the gooseneck and tailing hose is 2 3/8 inch inner diameter. The engines in our target horsepower range (60-80hp) have 2 inch exhaust, so a reducer (expander?) will be inline near the top of the loop. Expanding the hose to 2 3/8 inch at the top to the “downhill” side will help the system to “breathe out” more of the exhaust pressure.
That is the idea at least.