[C320-list] C320 exhaust syphon breaker valve

[Charles Munro via C320-list]

Hi all
I have been having a discussion with a friend (who has a Catalina 34) about the design of the exhaust syphon breaker, and the possible circumstances that it would be required.
Mine is located in the port cockpit locker, high up on the hull
Can anyone enlighten me please
Charles Munro
Sabi Star 2005 # 1011
Sent from my iPad

[Michael Stumpfoll via C320-list]

My ‘98 C320 had the siphon break in the locker. The previous owner disconnected and jury rigged a valve that fit inside the engine enclosure. When I bought the boat this past May the rear cylinder closest to exhaust was rusted solid. My son and I replaced the engine, shaft, stuffing box, cutlass, etc this summer.

Not sure what previous owner wanted to achieve with eliminating the circuit to the siphon break in the locker. I measured the cabin floor is around 15” below the water line. The top of the engine enclosure is not high enough for a siphon break. If anything, penetrate through the enclosure and mount the siphon break high on the bulkhead in the aft cabin. Enclose with something decorative.
Thanks,
Mike Stumpfoll

On Oct 11, 2025, at 11:03 PM, Charles Munro via C320-list <c320...@lists.catalina320.com> wrote:

Hi all

[surprise thompson87.com via C320-list]

My understanding is that the siphon of concern would be from the raw water thruhull and strainer, through the raw water pump and heat exchange, to the exhaust elbow. Such a siphon could occur if the exhaust elbow were to be below the water line. The danger would be that the muffler and exhaust line would fill with sea water that would back up through the exhaust valves into the cylinders. To prevent this you want a siphon break that is well above the water line while sailing with the engine off. The designers apparently thought that high in the port locker was the best option. Ideally it would be high on centerline, but the engine compartment probably isn’t high enough.

> On Oct 11, 2025, at 11:03 PM, Charles Munro via C320-list <c320...@lists.catalina320.com> wrote:
>

> Hi all

[Troy Dunn via C320-list]

Scott nailed it. There simply is not enough room in the engine
compartment to get the siphon break the required "at least 18 inches" above
the waterline when heeled over. The high spot in the cockpit locker is
probably barely high enough for folks that love to heel the boat way over.

Troy Dunn
Hull #514