HG02
Mate had a small fish blocking his sea cock hose starved the cooling system warning buzzer when off shut it down . He carries a piece of wire to clear out any thing in there a old car aerial would be good have
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Yes I've had that happen twice, straight after each other, the first fish was there for a couple days, man was it foul

The Engine is going!
Well having spent a day on my back,torn muscle, yesterday I’m much improved today. First job today was the diesel engine. Checked the oil first and it was black, normal for diesel engines so no water has entered the system. Next off came the impeller cover and there it was, all busted up! ere That was a great relief and even more so when all the bits were there. After replacing the impeller I next checked the whole system for blockages and found none. While doing this I was soaking then head of the leaky anti-syphoning devise, which is brass, in vinegar to clean it. With everything back in place I starter her up and away she went, no trouble at all. Mind you all this took two hours to carry out and I am sure that I would not have been able to do it at sea. So no sooner had I completed the engine repairs when these blokes on the trawler upwind of me started sanding the damn thing. With all their fiberglass and paint dust falling on us there was no option but to move to the other side upwind. So after that had a general clean-up and organised the lift-out at Horizon Shores for next Tuesday morning at 0800. In the meantime I will go up to Russell Island and visit a couple of friends there before returning next Monday afternoon to Jacob Wells. Haven’t had a chance yet but have to check the outboard as it would not start when I was returning from a visit to SV Argos yesterday morning. They had to tow me back to Seaka. 27 56.843 153 25.442

The anti-siphoning device is that for when you lift the boat out NSW . Im always worries about any restriction . When I lift out I shut the sea cock off and open it when back in the water.
Or do you need it so the engine cooling system raw water doesn't drain back?

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HG02 said..
The anti-siphoning device is that for when you lift the boat out NSW . Im always worries about any restriction . When I lift out I shut the sea cock off and open it when back in the water.
Or do you need it so the engine cooling system raw water doesn't drain back?

Not sure why a Tophat has an anti siphon device.

Most of the anti-siphon fittings I have seen go between the raw water engine outlet and the exhaust elbow to stop water flooding into the exhaust hose and engine cylinders if they happen to lie below the water line or close to it. This will happen when the engine is shut off.

Thanks for clearing that up for me
Jolene

Mine is installed as per the Nanni installation instructions in the raw sea water line before the pump on the engine. The engine is below sea level [its not rising either] and with the only opening to the engine below sea level is the intake for the raw sea water it needs a break to prevent syphoning through the raw cooling system into the exhaust system and then into the engine head. The exhaust is above water but has a syphon preventer as well.

My preventer was leaking because of a build up of salt deposits and low suction [failure over time of the impeller]. The device is as shown in whitworths cat as a Nanni anti-syphon.

All working fine now and at a slightly lower temperature, so must have been failing for some time.

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nswsailor said..
Mine is installed as per the Nanni installation instructions in the raw sea water line before the pump on the engine.

That is interesting , I cant see how you could have a siphon breaker before your raw water pump otherwise the vacuum from the pump would pull air through it. (may be the Nanni type is a special case). It could go after the raw water pump as positive pressure from the pump will keep the siphon breaker closed. I would be inclined to think that a siphon breaker before the pump could cause raw water pump failure.

I'm inclined to agree with Jolene on this one.

I bought a Nanni syphon break & installed it after the raw water pump (on a Ford), my engine intake is also below water level, because I was under the impression that the water is best being pushed through rather than sucked through the syphon break.

Your system must be working though!!

I would have thought the pump impeller would break any siphon


My sea level is at the top of the pump housing.
Id like to see where and how your pumps hoses run NSW

To me if there was any air getting into the system before the pump I might stave the pump and destroy a impeller worst case
scenario.
www.maritimusboote.de/Syphon-breaker-for-Nanni-Diesel-Engine-4150-HE
Does it look like the one in this link above NSW?

From what Ive read the anti siphon would be better fitted just before the water injection at the motor engine exhaust pipe as this is suppose to stop water filling up th exhaust manifold and back tracking into a open exhaust valve and damaging the motor
you shoiuld get your engine manual out and go throught it just in case like all humans we stuff up even L.C. does some times

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HG02 said..
I would have thought the pump impeller would break any siphon

The impeller will break the syphon (while it is new) however, all it needs is to lose one blade & stop in the right/wrong spot & you have an engine full of water or possibly a sunken boat!

The idea of this design is to stop water entering the engine via a open exhaust valve

I cant see why you should have a anti siphon before the pump or before the engine
the red in this diagram is the exhaust gases and blue above is the raw water cooling water after its been through the heat transfer or through the engine depending if you have raw water cooling of a fresh water cooling this stops the siphon process so it wont back fill the exhaust system and enter the engine via a exhaust valve that may be open

Or another way to think about it image a glass of water sitting in front of you and you have a straw to suck it up with, but I put a hole in the straw what happens then

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Here is the picture from a Nanni Instruction Manual. Not a good picture, but the wording in the Nanni Installation Manual makes it pretty clear. A raw water pump can stop the flow of water under normal conditions but if it losses its blades, then the Anti-siphon starts doing its job before the boat sinks.


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Must be at the end of raw water piping before exhaust elbow inlet

To me that makes no sense my used raw water exits at the "Green OE" if I was fitting a anti siphon Id fit it there not before the water enters the engine of cooling system. the engine is fully seal against any water entering it the only place it can enter is at the engine exhaust pipe where the water injection enters the system to cool the exhaust tubing on the way out

you could run outlet hose direct to out side hull but this would not cool the exhaust tubing before it exits the boat

The water all it does is cool the exhaust gases so they don't melt any hoses on the exhaust system between the engine and the hull outlet

When I shut my engine off I also turn the engine sea cock off
Crusoe your diagram looks like the anti siphon is before the motor its not a really good diagram

How can a boat sink from this???? other than if you don't turn off your sea cocks same as your head . Id never trust a hose clamp or any hose

When I bought my boat this was the seacock to sea strainer hose this section was hidden under my engine sump the sea cock was one inch and the sea strainer 3/4 I motored for 7 or 8 hours with this I never leave a sea cock open after I finished what it was open for
Even the surveyor dig not find this
had the boat surveyed during the 8 motoring hours

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HG02 said..


The idea of this design is to stop water entering the engine via a open exhaust valve

I cant see why you should have a anti siphon before the pump or before the engine
the red in this diagram is the exhaust gases and blue above is the raw water cooling water after its been through the heat transfer or through the engine depending if you have raw water cooling of a fresh water cooling this stops the siphon process so it wont back fill the exhaust system and enter the engine via a exhaust valve that may be open

Or another way to think about it image a glass of water sitting in front of you and you have a straw to suck it up with, but I put a hole in the straw what happens then

This is how it should be IMO.

Your analogy of the straw HG is why I have the vent after the pump as in this diagram.

I think it just a bad/unclear diagram that Crusoe posted.

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HG02 said..

I never leave a sea cock open after I finished what it was open for

I have to leave my sea cock open to feed the fridge which is on 24/7

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Lazzarae said..

HG02 said..


The idea of this design is to stop water entering the engine via a open exhaust valve

I cant see why you should have a anti siphon before the pump or before the engine
the red in this diagram is the exhaust gases and blue above is the raw water cooling water after its been through the heat transfer or through the engine depending if you have raw water cooling of a fresh water cooling this stops the siphon process so it wont back fill the exhaust system and enter the engine via a exhaust valve that may be open

Or another way to think about it image a glass of water sitting in front of you and you have a straw to suck it up with, but I put a hole in the straw what happens then

This is how it should be IMO.

Your analogy of the straw HG is why I have the vent after the pump as in this diagram.

I think it just a bad/unclear diagram that Crusoe posted.

Lazzarae your right I looked at the diagram not the written explanation sorry for that

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Lazzarae said..

HG02 said..

I never leave a sea cock open after I finished what it was open for

I have to leave my sea cock open to feed the fridge which is on 24/7

I would fit a sea cock just for that purpose other wise lazza Id have to sleep with one foot on the floor to judge how deep the sea water was getting above floor level , before I need to man the bilge pump

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HG02 said..

I would fit a sea cock just for that purpose other wise lazza Id have to sleep with one foot on the floor to judge how deep the sea water was getting above floor level , before I need to man the bilge pump

Actually I have 2 sea cocks - one for the motor & one for the heads, deckwash etc.
They are connected by a crossover pipe with a tap that is usually shut. If I get a blockage in my main engine feed I can quickly open this tap to feed the motor to get me out of trouble.

I know that the Nanni vented loop works because I installed it after my sump was full of water the day after I launched the boat.

Yep the drawing I posted from the Nanni Installation manual is very misleading and could easily end up leading to someone installing the Anti-siphon in the wrong location.

Sorry HG02, I shouldn't have written the boat may sink. I should have said water may enter the cylinder head via the exhaust manifold if the blades come off the raw water pump. Hence the need for an Anti-siphon device.

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Lazzarae said..

HG02 said..
I would have thought the pump impeller would break any siphon

The impeller will break the syphon (while it is new) however, all it needs is to lose one blade & stop in the right/wrong spot & you have an engine full of water or possibly a sunken boat!

Not if you make a habit of closing the sea cock when the engine is shut down.

The diagrams that have been posted both are correct..
The siphon breaker is basically put there to protect the engine from flooding with water, It would be hard to sink a boat but stranger things have happened, given time water may find its way out of an engine flooded with water.
I have a "PSS" seal water feed from the raw outlet that is connected through a tee. It has to be connected before the siphon breaker or water from the PSS will flood my below water line exhaust and engine.

nswsailor, I would defiantly have another look in your manual, the position of that siphon breaker may have caused your pump failure

to me saying fitting a siphon after the pump is not describing it well . I maybe wrong here but I feel the anti siphon should be fitted at the end of the cooling system circuit just before the cooling water enters the exhaust system.
The only way water can enter the sump is via the head gasket leaking or a open exhaust valve meaning water in the combustion chamber and running down past the pistons

As a Kid I saw a very large Bulldog tractor rocking on a channel back for years and eventually it rolled into the channel and the intake sucked a full cylinder of water into it and have no where to go so it made a banana con rod to slow it self down to a stop in a milli seconds

Siphon breaker loops and vents are really only relevant when the engine is mostly below the water line but even then not totally necessary.

Anti siphon vents have a habit of salting up and sticking open or shut.

Even if the exhaust outlet is below the water line a water trap fitted just after the mixing elbow should eliminate any back flushing to the engine without the need for high loops just before the exit from the hull.

as Cisco said I fitted a vetus a water lock muffler
did have one of these inside the engine bay but moved it back behind the mizzen bulkhead


30 years it was cracked in a couple of places

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nswsailor said..
Mine is installed as per the Nanni installation instructions in the raw sea water line before the pump on the engine. The engine is below sea level [its not rising either] and with the only opening to the engine below sea level is the intake for the raw sea water it needs a break to prevent syphoning through the raw cooling system into the exhaust system and then into the engine head. The exhaust is above water but has a syphon preventer as well.

My preventer was leaking because of a build up of salt deposits and low suction [failure over time of the impeller]. The device is as shown in whitworths cat as a Nanni anti-syphon.

All working fine now and at a slightly lower temperature, so must have been failing for some time.

Thats good to hear mate.
Were making slow progress up the NSW coast at the moment.
Apart from being bloody cold the damn westerlies want to blow s to New Zealand every day.
we will be in Port Macquarie on Friday, hopefully. Sitting in Forster/Tuncurry at the moment.

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cisco said..

Siphon breaker loops and vents are really only relevant when the engine is mostly below the water line but even then not totally necessary.

Anti siphon vents have a habit of salting up and sticking open or shut.

Even if the exhaust outlet is below the water line a water trap fitted just after the mixing elbow should eliminate any back flushing to the engine without the need for high loops just before the exit from the hull.

I'm with you there cisco. I still can't get around the idea that the cylinder head is below the waterline in a Tophat. Siphons are just something else to go wrong. If the cylinder head is above the waterline and the waterlock muffler is below as well I fail to see how water can enter the cylinder head after shut down.

HG02,
If I had a glass of water with a straw in it and the straw had a hole in it I would have two options,

1. Get another straw

2. Drink straight from the glass

Quite an easy solution.

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Ramona said..

cisco said..

Siphon breaker loops and vents are really only relevant when the engine is mostly below the water line but even then not totally necessary.

Anti siphon vents have a habit of salting up and sticking open or shut.

Even if the exhaust outlet is below the water line a water trap fitted just after the mixing elbow should eliminate any back flushing to the engine without the need for high loops just before the exit from the hull.

I'm with you there cisco. I still can't get around the idea that the cylinder head is below the waterline in a Tophat. Siphons are just something else to go wrong. If the cylinder head is above the waterline and the waterlock muffler is below as well I fail to see how water can enter the cylinder head after shut down.

Yes, I think Vetus and others make quite a bit of money out of selling items that are not really needed.

my Vetus wet lock is mainly for a just in case scenario of a wave forcing sea water up my exhaust while sailing and running the exit water low out of the engine pipe and a little bit of extra quiet inside the boat