Anti-Siphon Loop for Raw Water Exhaust

[Wotname]

Originally Posted by GordMay

✓ You recall correctly.

Pressure can be converted to head by the following formula:
Head = (Pressure x 2.31*) ÷ Specific Gravity

* 2.31 feet of fresh water equals 1 psi.

If atmospheric pressure is 14.7 psi at sea level, and we are talking about fresh water (sg.1); 14.7-psi. would convert to 33.96* feet of head:
Head = (14.7 x 2.31) ÷ 1 = 33.96 Feet*

* In actual practice, friction in the hose will reduce that theoretical head to something around 32'.

Seawater (@36 Deg) has an SG of 1.02, thus:
Head = (14.7 x 2.31) ÷ 1.02 = 33.39 Ft. (less friction loss).

And thanks for the primer - it all comes flooding back now…

Now what else have I forgotten

[Snowpetrel]

Originally Posted by Wotname

Yes, this is actually on my "to do" list. Just waiting for some more gas before welding up a nice custom fitting to take the tell tale water into the cockpit - directly above one of the drains!

Nothing quite like seeing the tell tale water going out to know all is good

Had one rigged like this on a boat I ran in antarctica. It was just high enough above the cockpit drain to slide a small bucket under the dribble of warm water. So we had lots of nice warm salty water on tap anytime we had the motor running. Very handy for warming up cold fingers and melting icy stuff. Even good for a prerinse of greasy dishes.

A mate hydraliced his engine a few times due to a blocked antisyphon vent. So I much prefer an open discharge that trickles water. Mine runs to deck level about 3 feet above the engine. It only dribbles at higher revs. Unfortunately its on the cold side of the system, so no nice hot water on tap...

[HappyMdRSailor]

Originally Posted by Hudson Force

That looks like something I tried in high school when I was too lazy to go to the pharmacy...

[Beausoleil]

Reviving this old thread, as I wasted most of my Memorial Day weekend dealing with this very issue.

Beausoleil has a Westerbeke Century Series T120-4A turbo charged diesel with a 4" exhaust system. The exhaust hose drops down to the water-lift muffler in the bilge, and then rises up to a non-vented fiberglass loop a bit over 30" above the waterline, then out a thruhull just above the starboard waterline.

I re-commissioned the engine the week before Memorial Day. On Saturday (30 May), I check the oil level and find it overflowing. Only one thing I know can cause that, so I open the oil sump drain hose and drain over a gallon of water from the sump! After that, I try starting the engine, and - sure enough - the damn thing was hydro-locked. I removed the glow plugs and blew all the water out by engaging the starter, put the thing back together and start it up.

I brought the engine up to operating temperature, then shut it down and drained the oil - now the color of chocolate milk. I refilled it with oil, ran it again, then drained it again. Filled it a second time, changed the oil filter, and ran it for an hour - oil's still clean...

To prevent this from happening again, I'm taking Wotname's advice and installing a vent line by drilling and tapping the fiberglass loop, installing a hose barb fitting, and running a vent line from it to an existing vent on the starboard topsides just below the gunwale, inline with the exhaust thruhull below. I'd always wondered what that unused vent was there for - probably for exactly this purpose. For whatever reason, when we repowered back in 2007/08, the boatyard doing the work neglected to install a siphon break vent in the exhaust loop. They installed one for the transmission oil cooler, but not for the main exhaust line.

One more project to add to the to-do list this weekend...

[Saltyhog]

Originally Posted by Beausoleil

...

To prevent this from happening again, I'm taking Wotname's advice and installing a vent line by drilling and tapping the fiberglass loop, installing a hose barb fitting, and running a vent line from it to an existing vent on the starboard topsides just below the gunwale, inline with the exhaust thruhull below. I'd always wondered what that unused vent was there for - probably for exactly this purpose. For whatever reason, when we repowered back in 2007/08, the boatyard doing the work neglected to install a siphon break vent in the exhaust loop. They installed one for the transmission oil cooler, but not for the main exhaust line.

One more project to add to the to-do list this weekend...

Generally, a vented loop is added to the raw water cooling loop from the heat exchanger to the exhaust elbow on the engine. It sounds like you are suggesting to add a vent on the exhaust hose itself. I'm not really sure what purpose that serves if you exhaust thruhull is above the waterline.

[Beausoleil]

Originally Posted by Saltyhog

Generally, a vented loop is added to the raw water cooling loop from the heat exchanger to the exhaust elbow on the engine. It sounds like you are suggesting to add a vent on the exhaust hose itself. I'm not really sure what purpose that serves if you exhaust thruhull is above the waterline.

It's a sailboat, so the exhaust (starboard side) is submerged when motor-sailing on a port tack, or when motoring in rough conditions.

OTOH - I should check the anti-siphon valve on the raw water vented loop (that also runs through a transmission cooler as I mentioned earlier). I hadn't considered that it may be the source of the water intrusion - it may be clogged... Thanks for pointing that out!

[svstrider]

Originally Posted by Saltyhog

Generally, a vented loop is added to the raw water cooling loop from the heat exchanger to the exhaust elbow on the engine. It sounds like you are suggesting to add a vent on the exhaust hose itself. I'm not really sure what purpose that serves if you exhaust thruhull is above the waterline.

Two questions I need help with.
1. On my catamaran, the exhaust water outlet is not under water when sailing, obviously. Although I know that wave action on the windward side could push water into the exhaust. I have a vetus wet muffler situated next to the engine mounts. There is also an exhaust hose loop as the exhaust hose exits the through hull.
Q = Is this enough to prevent hydolocking. I have had the boat 8 years without sign of water in the oil. Sailed through plenty of nasty weather in the last 5 years living aboard.

2. On my 3GM30 (yr 2000) raw water cooled Yanmars there is no scope for venting between the exhaust manifol & elbow as the water is conveyed through the engine block to the exhaust elbow. Later model has a rubber hose instead.
Q = If I do need an antisiphon where and how do I situate it?

[four winds]

Do you not have the hose pictured between the manifold and the elbow? This hose should be vented, though it is not pictured with one in the manual.

True the water flows from the block, to the head, into the manifold, but it travels in separate passages from the exhaust gases. It exits the manifold through the rear hose and mixes in the elbow.

Edit,.... Sorry the pic is upside down. One day I'll figure that out.

[svstrider]

Originally Posted by four winds

Do you not have the hose pictured between the manifold and the elbow? This hose should be vented, though it is not pictured with one in the manual.

True the water flows from the block, to the head, into the manifold, but it travels in separate passages from the exhaust gases. It exits the manifold through the rear hose and mixes in the elbow.

Hi 4Winds,
Unfortunately, on my model 3GM30, Jap made circa 2000, there is NOT a hose from out of the top of the manifold then into the elbow. Crazy as it seems, there is a hole through the end of the manifold leading water into the exhaust elbow! Hence no way of venting. Also this small ID hole in the manifold blocks easily.

A design fault that I guess they remedied later. I have to be careful when ordering new exhaust elbows to make sure I get the older type and not the one as shown in the workshop manual. I have a blow up of the cooling system of my engine on the boat. However, as I am playing around on a seismic vessel going around in circles off Guyana, I can't send you a copy. I will keep searching my files on my laptop here. i am sure I have the diagram some where.

Do other cat owners vent their engines at this point or any where along the exhaust line?

[four winds]

Well that is something I have not seen before. Strange.

And curiously strange since if I recall correctly the 3gm30f in my boat was installed in 2000. There is an invoice onboard I can check tomorrow. Time to sleep right now.

[RaymondR]

Originally Posted by svstrider

Two questions I need help with.
1. On my catamaran, the exhaust water outlet is not under water when sailing, obviously. Although I know that wave action on the windward side could push water into the exhaust. I have a vetus wet muffler situated next to the engine mounts. There is also an exhaust hose loop as the exhaust hose exits the through hull.
Q = Is this enough to prevent hydolocking. I have had the boat 8 years without sign of water in the oil. Sailed through plenty of nasty weather in the last 5 years living aboard.

2. On my 3GM30 (yr 2000) raw water cooled Yanmars there is no scope for venting between the exhaust manifol & elbow as the water is conveyed through the engine block to the exhaust elbow. Later model has a rubber hose instead.
Q = If I do need an antisiphon where and how do I situate it?

The Vetus thingy is not a muffler it acts as a reservoir so that water draining back from the large overboard exhaust hose will be stored rather than flood back into the engine.

If you have not back flooded water into the engine in 8 years it is fairly probable that it will not happen unless the circumstances are very unusual - sort of thing like inverting the boat, never advisable and definitely not in a cat.

You can have the anti syphon loop anywhere in the cooling water circuit between the pump and the exhaust manifold. I put mine directly after the pump high in a wet gear locker as the water is always cool there and I was able to use clear plastic tubing. They are a cheap, easily implemented precaution against accidental flooding of the engine to fit and don't usually require any maintenance. The clear plastic tubing allows one to see the water level draining down in the tube.