Cruisers Forum
 


Reply
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 09-08-2020, 10:05   #1
Registered User

Join Date: Jul 2019
Location: New York
Boat: Cape Dory 27 - 1978
Posts: 73
Raw Water Anti Siphon Vented Loop

What are people's thoughts about anti-siphon valves on the raw water system of a diesel engine? The exhaust of my boat is halfway up the transom, so I do not believe it is possible to siphon water into my boat.

In addition, I don't want to start this debate, but it concerns opening and closing the raw water seacock. If the engine seacock is open, will it flood the engine with raw water, or will it be held back by the height of the mixing elbow which is above the waterline, and would an anti-siphon valve solve this problem or provide better peace of mind?
__________________
"Haul Away Joe"
Sailor_Grant is offline   Reply With Quote
Old 09-08-2020, 10:38   #2
Registered User
 
wingssail's Avatar

Join Date: Jan 2010
Location: On Vessel WINGS, wherever there's an ocean, currently in Mexico
Boat: Serendipity 43
Posts: 2,280
Send a message via AIM to wingssail Send a message via Skype™ to wingssail
Re: Raw Water Anti Siphon Vented Loop

Quote:
Originally Posted by Sailor_Grant View Post
What are people's thoughts about anti-siphon valves on the raw water system of a diesel engine? The exhaust of my boat is halfway up the transom, so I do not believe it is possible to siphon water into my boat.

In addition, I don't want to start this debate, but it concerns opening and closing the raw water seacock. If the engine seacock is open, will it flood the engine with raw water, or will it be held back by the height of the mixing elbow which is above the waterline, and would an anti-siphon valve solve this problem or provide better peace of mind?
The issue is not seawater syphoning in from the exhaust outlet at the transom.

The problem is that raw water in the cooling system can run from the heat exchanger outlet into the mixing elbow (if that is below the water line). Then the exhaust system fills up until the water level backs up into the exhaust manifold and then in to any open exhaust valve, and into the cylinder. This can occur if the top of engine is below the waterline. Closing the seacock prevents this. The other thing which saves the engine is that the exhaust pressure when the engine is running blows water out the exhaust and prevents it from filling the exhaust manifold.

The anti-syphon break is installed between the heat exchanger outlet and the exhaust mixing elbow. Often all that is needed is a long loop in the hose with a "T" at the highest point opening into some draining point in the boat (galley sink or cockpit drain, for example). When the engine is running a small amount of water is ejected out the "T" but when the engine is turned off air enters that "T" and prevents raw water from being syphoned over the loop and into the exhaust system. For this reason an electric raw water pump which runs when the engine is not operating is dangerous, because it can fill the exhaust system.

Now, if you have a exhaust outlet below the waterline it could be possible for seawater to syphon back to the engine through the exhaust hose, so it is a good idea to have a high loop in the exhaust hose, and use a large hose, so that raw water runs out of the hose and the syphoning effect cannot work.

Finally, there is some concern that a following sea will strike the exhaust outlet and force water backwards into the engine, running or not. Some owners install a valve in the exhaust hose to prevent that while the engine is not running, however it cannot be closed when the engine is operating. I have this valve but have never closed it. My exhaust outlet is actually very close to the water's surface at the transom, but that problem has just never occurred.

A flap over the exhaust outlet could prevent a wave from entering without restricting the escape of exhaust water and gases.
__________________
Sailing is a sport, an athletic activity, not a sedentary one.
Fred Roswold-Fred & Judy, SV Wings, Mexico
https://wingssail.blogspot.com/
wingssail is offline   Reply With Quote
Old 09-08-2020, 10:43   #3
Registered User

Join Date: Aug 2009
Location: between the devil and the deep blue sea
Boat: a sailing boat
Posts: 20,013
Re: Raw Water Anti Siphon Vented Loop

The break breaks the intake water, not the exhaust water.


All boats I have sailed on had one.



barnakiel
barnakiel is offline   Reply With Quote
Old 09-08-2020, 10:51   #4
Registered User

Join Date: Jul 2019
Location: New York
Boat: Cape Dory 27 - 1978
Posts: 73
Re: Raw Water Anti Siphon Vented Loop

So if the mixing elbow intake is above the waterline by 6 inches a vented loop is not necessary?
__________________
"Haul Away Joe"
Sailor_Grant is offline   Reply With Quote
Old 09-08-2020, 11:18   #5
Registered User

Join Date: Oct 2019
Location: Kennebunk ME
Boat: Owner built 60í Aluminum Expedition Yacht.
Posts: 289
Re: Raw Water Anti Siphon Vented Loop

Hi. There are two ways to drown the engine or generator. First, exhaust.
Power yachts often have issues with following seas. There is an exhaust builder in Miami who has some excellent pages on the subject. Since you have a smaller engine, you might consider a water / exhaust gas separator. Add a drain valve to your water lift muffler so cranking your engine will not fill it too much.
Iím tired of going into the engine room to open and close my raw water valve so Iím adding a motorized full flow valve with auto off and a light and switch next to my generator start panel. Hope you are not this old and a bit more nimble. A valve and a wood reminder stick on your engine key will work fine.
Happy trails.
Mark a hobbling manatee
Manateeman is offline   Reply With Quote
Old 09-08-2020, 11:53   #6
Registered User
 
wingssail's Avatar

Join Date: Jan 2010
Location: On Vessel WINGS, wherever there's an ocean, currently in Mexico
Boat: Serendipity 43
Posts: 2,280
Send a message via AIM to wingssail Send a message via Skype™ to wingssail
Re: Raw Water Anti Siphon Vented Loop

Quote:
Originally Posted by Sailor_Grant View Post
So if the mixing elbow intake is above the waterline by 6 inches a vented loop is not necessary?
No, what matters is the height of the injection point, (water hose going into the mixing elbow). If that injection point is below the waterline the raw water in the heat exchanger will flood the exhaust system unless a syphon break is present. It may syphon over quite high loops (including exhaust mixing elbows) and into the exhaust manifold.

If any portion of the exhaust manifold is below the waterline, even with a higher mixing elbow, a wave or heeling may allow the mixing elbow to fill and then syphoning can occur there also. The syphon break in the hose prior to the injection point prevents the exhaust system from filling.
__________________
Sailing is a sport, an athletic activity, not a sedentary one.
Fred Roswold-Fred & Judy, SV Wings, Mexico
https://wingssail.blogspot.com/
wingssail is offline   Reply With Quote
Old 09-08-2020, 12:05   #7
Registered User
 
S/V Illusion's Avatar

Join Date: Oct 2007
Location: Lakewood Ranch, FLORIDA
Boat: Alden 50, Sarasota, Florida
Posts: 2,452
Re: Raw Water Anti Siphon Vented Loop

Quote:
Originally Posted by Sailor_Grant View Post
So if the mixing elbow intake is above the waterline by 6 inches a vented loop is not necessary?
Depends on wave height as well as how much heel or stern squat occurs.
S/V Illusion is offline   Reply With Quote
Old 09-08-2020, 12:21   #8
Registered User
 
Cheechako's Avatar

Join Date: Aug 2006
Location: Skagit City, WA
Posts: 22,873
Re: Raw Water Anti Siphon Vented Loop

Water does come in from the exhaust. Not uncommon at all. I had one boat it happened because the boat was sitting at an outside dock that got some wind chop action on the stern. Evidently it pumped water into the rear cylinder one splash at the exhaust outlet at a time, eventually filling the exhaust muffler and hose until it reached that cylinder.
__________________
"I spent most of my money on Booze, Broads and Boats. The rest I wasted" - Elmore Leonard











Cheechako is offline   Reply With Quote
Old 10-08-2020, 09:49   #9
Registered User

Join Date: Jun 2009
Location: Annapolis, MD
Boat: Gozzard, 44CC, 50'
Posts: 318
Re: Raw Water Anti Siphon Vented Loop

Doesn't your raw water pump's impellers prevent siphoning thru your raw water sea-cock?
Scrimshaw4 is offline   Reply With Quote
Old 10-08-2020, 10:01   #10
Registered User

Join Date: Nov 2017
Location: Portland, Oregon USA
Boat: Island Packet, Packet Cat 35
Posts: 502
Re: Raw Water Anti Siphon Vented Loop

As a safety measure to protect your engine, why wouldn't you put in a siphon break? There was mention of not needing one because the mixing elbow is 6" above the water line. Is that true if you're heeled over? Perkins engines were notorious for back siphoning. Mine did it twice at the dock.
Cpt Mark is offline   Reply With Quote
Old 10-08-2020, 10:26   #11
Registered User
 
Stu Jackson's Avatar

Join Date: Jan 2011
Location: Cowichan Bay, BC (Maple Bay Marina)
Posts: 8,267
Re: Raw Water Anti Siphon Vented Loop

Diagram might help
Attached Images
 
__________________
Stu Jackson
Catalina 34 #224 (1986) C34IA Secretary
Cowichan Bay, BC, (Maple Bay Marina) SR/FK, M25, Rocna 10 (22#) (NZ model)
Stu Jackson is offline   Reply With Quote
Old 10-08-2020, 11:09   #12
Registered User
 
Cheechako's Avatar

Join Date: Aug 2006
Location: Skagit City, WA
Posts: 22,873
Re: Raw Water Anti Siphon Vented Loop

Quote:
Originally Posted by Scrimshaw4 View Post
Doesn't your raw water pump's impellers prevent siphoning thru your raw water sea-cock?
Apparently they generally do. But it only takes that one time. Strangely, most of my boats never had the siphon break. The only boat I had an issue with had a siphon break , but it was an exhaust ingress issue.
__________________
"I spent most of my money on Booze, Broads and Boats. The rest I wasted" - Elmore Leonard











Cheechako is offline   Reply With Quote
Old 10-08-2020, 14:12   #13
Registered User
 
wingssail's Avatar

Join Date: Jan 2010
Location: On Vessel WINGS, wherever there's an ocean, currently in Mexico
Boat: Serendipity 43
Posts: 2,280
Send a message via AIM to wingssail Send a message via Skype™ to wingssail
Re: Raw Water Anti Siphon Vented Loop

Quote:
Originally Posted by Scrimshaw4 View Post
Doesn't your raw water pump's impellers prevent siphoning thru your raw water sea-cock?
Not generally, the impellor, when stopped, will permit water to flow past the blades. This is not syphoning. The raw water pump is often below water level and the water flows freely past the impellor.
__________________
Sailing is a sport, an athletic activity, not a sedentary one.
Fred Roswold-Fred & Judy, SV Wings, Mexico
https://wingssail.blogspot.com/
wingssail is offline   Reply With Quote
Old 11-08-2020, 10:04   #14
Registered User

Join Date: Feb 2015
Location: Somewhere warm
Boat: Morgan 462
Posts: 1,243
Re: Raw Water Anti Siphon Vented Loop

Quote:
Originally Posted by Sailor_Grant View Post
So if the mixing elbow intake is above the waterline by 6 inches a vented loop is not necessary?

Strictly speaking, yes, but what's the resistance to spending a few bucks and a couple hours work to protect your engine from a possibility of flooding, no matter how remote?

Exhaust elbow only six inches above waterline would not make me feel comfortable about not having a vented loop.
__________________
No shirt, no shoes, no problem!
waterman46 is offline   Reply With Quote
Old 11-08-2020, 12:42   #15
Registered User
 
HeinSdL's Avatar

Join Date: Apr 2018
Location: Switzerland
Boat: X-Yachts X442
Posts: 229
Re: Raw Water Anti Siphon Vented Loop

Checking the proper operation of the anti syphon valve yearly is thus to be recommended (extremely simple, it's just a spring loaded device allowing air into the system when the pressure inside drops). The small valve can get stuck in place leading to problems.
HeinSdL is offline   Reply With Quote
Reply

Tags
raw water, water

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Vented loop/Siphon break on Leopard cats B4A Leopard Catamarans, Robertson & Caine 0 07-09-2019 23:19
Anti-Siphon Loop for Raw Water Exhaust Hudson Force Engines and Propulsion Systems 40 14-06-2016 00:10
Servicing Raw Water Vented Loop - Vetus MarkJ Engines and Propulsion Systems 7 27-06-2013 09:41
Plastic Anti-Siphon Valve for Vented Loop Dick Locke Plumbing Systems and Fixtures 4 17-07-2009 22:49

Advertise Here


All times are GMT -7. The time now is 02:28.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2020, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.