Siphon Break - Engine Raw Water Circuit

[rardiH36]

Imbedded in recent threads is a picture (courtesy of Maine Sail) that highlights a siphon- break in the raw water circuit of an engine's cooling system.

My boat’s engine lacks this feature. (1980 Cherubini Hunter 36 with Yanmar 2QM 20H raw water-cooled model that has been converted to coolant cooling with the addition of an external impeller pump for the raw water circuit and a heat exchanger mounted on a bulkhead).

How important is the anti-siphon break? The boat has been around 28 years, presumably without one the entire time. My Yanmar manual mentions a siphon loop/break as an option if the (otherwise) highest point of the circuit less than 18 inches above the water line. I have not measured, but my guess is that the highest point of my circuit, the heat exchanger actually) is 12-15” above the water line. I’ve read that the siphon-break can be either between the water pump and the heat exchanger. Or between the heat exchanger and the exhaust elbow. Other than this fact, what else needs to be known for adding the break?

Thanks and regards,
rardi

 

[Bill Roosa]

You need...

to identify a place where you can get 18+" above the waterline so you can install it.

I saw a set up that just had a tube run into the cockpit corner. The heated water came from the raw water system (tee connection) between the heat exchanger and elbow, ran along the cockpit and then flowed down the scuppers. I gave instant proof that raw cooling water was flowing, gave around 20" of height above water level and never "salted up". His comment was that it gets kinda steamy if I plug up the scupper and take a bath in warm sea water!!

As long as you have the circuit "vented to the atmosphere well above the heeled water line" somewhere around the heat exchanger you will be OK.

 

[rardiH36]

Re: You need...

Dear Bill:

Thanks the info. Given that the boat has been successfully floating (to the best of my knowledge) for 28 years, adding the break at 18"+ above the water line probably isn't a rush project. Although the cooling system tubing looks OK, I have a suspicion that it's been quite some time since it was replaced. I'll put in the siphon break at the same time as this maintenance item.

Plumbing the heated raw water into the cockpit as a heated jacuzzi is an intriguing dual purpose idea. But I'll pass on this one.

 

[Ron20324]

I have not seen every boat ever made, but is the siphon used on any manufaturere's boats? I have never heard of this in the all-important raw water line. I know the purpose of a siphon, and not sure why you want to add one to the raw water, but I'll listen to reason.

 

[sailaway78]

Some things I don't understand

I really don't understand the need for a anti siphon valve when the exhaust is above the water line. Mine is well above the water line, unless motoring pretty hard, then the exhaust is below, but not by much. Yet I have an anti siphon valve, I assume factory installed. Exactly what am I missing here.

 

[Bill Roosa]

It's the low spot in the circuit not the outlet

If the low spot in the circuit is below the water line then it is possible for a following sea and busted rubber hose/muffler to allow water to start and then siphon in.
If the whole system is above the water line then there is no need for an anti siphon loop.

The instructions on both engine install and muffler install cover this in detail BTW. Not that I ever read those things but I was thumbing through my manuals looking for my latest copy of Latitudes and Attitudes and saw it out of the corner of my eye.

 

[Maine Sail]

I have not seen every boat ever made, but is the siphon used on any manufaturere's boats? I have never heard of this in the all-important raw water line. I know the purpose of a siphon, and not sure why you want to add one to the raw water, but I'll listen to reason.

It is not installed on the suction side but rather between the pump and HX or between the HX and exhaust elbow on the output side. Siphon breaks do not work on suction lines and it totally defeats the purpose. The little vent seals when it senses "pushing" flow. When you shut down the engine the water naturally wants to settle and the little valve opens up to let air in and break any siphoning..

I have rarely ever seen a boat without a siphon break on the engine install. It is important to get them as high as possible and as close to the center-line as possible. I prefer to install them between the HX and exhaust elbow as it gives you a lot more room to work with..

Here's a 2005 Catalina and the siphon break.

While not necessary on each and every specific install it is rare that a sailboat would not need one with the engines sitting so low in the hull.


From the Westerbeke Marine engine installation manual:

SIPHON-BREAK
For installations where the exhaust manifold/water injected exhaust elbow is close to or will be below the vessel’s waterline, provisions must be made to install a siphon break in the raw water supply hose to the exhaust elbow. This hose must be looped a minimum of 20” above the vessel’s waterline. Failure to use a siphon-break when the exhaust manifold injection port is at or below the load waterline will result in
raw water damage to the engine and possible flooding of the boat.
If you have any doubt about the position of the water-injected exhaust elbow relative to the vessel’s waterline under the vessel’s various operating conditions, install a siphon-break.
NOTE: A siphon-break requires periodic inspection and cleaning to ensure proper operation. Failure to properly maintain a siphon-break can result in catastrophic engine damage. Consult the siphon-break manufacturer for proper maintenance.

Westerbeke Installation Manual (LINK)


P.S. This was the second item addressed in the manual right below a paragraph stating to adhere to codes and standards of practice when installing the engine. Westerbeke thinks siphon breaks are of very high importance! Also the picture on the cover shows a siphon break..

 

[Maine Sail]

I really don't understand the need for a anti siphon valve when the exhaust is above the water line. Mine is well above the water line, unless motoring pretty hard, then the exhaust is below, but not by much. Yet I have an anti siphon valve, I assume factory installed. Exactly what am I missing here.

N&E,

The raw water supply siphonbreak is to prevent siphoning of the raw water circuit not to prevent exhaust water from following seas.

Raw water pumps are not valves, check valves or positive shut offs. The raw water pump can continue to siphon raw water into the engines exhaust system until full, after shut down, if conditions are right.

There was a guy at my boat yard who had never had a siphon event until he was motor sailing in some heavy winds with high angles of heel. He shut the engine down and because he was heeled, and the siphon break was not high enough, and off center he began a siphon and flooded his engine because the siphon break was below the heeled water line before it had a chance to actually break the siphon. All it takes is a little air in the top of a loop and a way for more air to be sucked in and you prevent a siphon event.