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22-11-2017, 18:09
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#1
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Registered User
Join Date: Sep 2010
Location: San Francisco, CA
Boat: 1980 Pearson 323 - 34ft LOA
Posts: 641
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Exhaust Plumbing Bypass Stern Squirt
I finally decided to replace my mixing elbow and noticed some curious plumbing. Please see image below.
It appears that there is a cooling water detour before reaching the mixing elbow. This little detour exits the boat just above the main exhaust.
Does anyone know the reason to route some of the water overboard before the mixing elbow?
I think the prior owner explain it was a way to see that the cooling water was flowing without having to look over the stern since it exits the boat in a thin squirting stream visible from the cockpit. (I don’t think he did the plumbing)
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22-11-2017, 18:30
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#2
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Registered User
Join Date: May 2010
Location: Sydney Australia
Boat: Fisher pilothouse sloop 32'
Posts: 3,413
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Re: Exhaust Plumbing Bypass Stern Squirt
My guess would be that small stream is from the vented loop or anti-siphon valve instead of a small rubber duckbill. Guarantees that the valve never stays closed
__________________
Rob aka Uncle Bob Sydney Australia.
Life is 10% the cards you are dealt, 90% how you play em
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22-11-2017, 20:30
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#3
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Marine Service Provider
Join Date: Jul 2004
Posts: 192
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Re: Exhaust Plumbing Bypass Stern Squirt
It is the anti siphon. Very important. Should be very small stream.
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22-11-2017, 22:42
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#4
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Registered User
Join Date: Jan 2012
Location: Australia
Boat: Catalina 470
Posts: 4,578
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Re: Exhaust Plumbing Bypass Stern Squirt
It's a good way of doing it. The little valves often get salted up which can cause a hydro lock, by having a small tube instead of a valve there is very little chance of a blockage, also you can visually see that it's ok,if waters coming out, you are right to go.
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22-11-2017, 23:49
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#5
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Registered User
Join Date: Sep 2010
Location: San Francisco, CA
Boat: 1980 Pearson 323 - 34ft LOA
Posts: 641
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Re: Exhaust Plumbing Bypass Stern Squirt
Ok, I see. I’m used to seeing the little duckbill like the head intake has.
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23-11-2017, 08:18
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#6
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Registered User
Join Date: Dec 2013
Location: Salt Lake City
Boat: Gulfstar 50
Posts: 48
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Re: Exhaust Plumbing Bypass Stern Squirt
It is also used to reduce exhaust system back pressure. Some lift mufflers, if they must lift some distance, create back pressure that is above the engine manufacturers spec. Bypassing part of the cooling water reduces this.
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23-11-2017, 08:22
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#7
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Registered User
Join Date: Jan 2012
Location: Australia
Boat: Catalina 470
Posts: 4,578
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Re: Exhaust Plumbing Bypass Stern Squirt
Quote:
Originally Posted by Mojadito
It is also used to reduce exhaust system back pressure. Some lift mufflers, if they must lift some distance, create back pressure that is above the engine manufacturers spec. Bypassing part of the cooling water reduces this.
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I don't understand this? How does water exiting through the exhaust create back pressure? replacing space that could be used for exhaust gas? Sorry, don't get it, no criticism.
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23-11-2017, 08:27
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#8
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Registered User
Join Date: May 2008
Location: Nova Scotia until Spring 2021
Boat: Custom 41' Steel Pilothouse Cutter
Posts: 4,976
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Re: Exhaust Plumbing Bypass Stern Squirt
Quote:
Originally Posted by daletournier
It's a good way of doing it. The little valves often get salted up which can cause a hydro lock, by having a small tube instead of a valve there is very little chance of a blockage, also you can visually see that it's ok,if waters coming out, you are right to go.
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This is the good way to do it. No spring, no plastic piston to seize. When needed, flush with fresh.
Or think differently and dispose of the anti-siphon completely.
http://www.cruisersforum.com/attachm...xhaust-med.jpg
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23-11-2017, 08:35
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#9
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Registered User
Join Date: Jan 2012
Location: Australia
Boat: Catalina 470
Posts: 4,578
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Re: Exhaust Plumbing Bypass Stern Squirt
Quote:
Originally Posted by S/V Alchemy
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Never seen this, but great idea if boat design enables you to do it. Impossible to siphon back.
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23-11-2017, 08:45
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#10
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Senior Cruiser
Join Date: Dec 2008
Location: Between Caribbean and Canada
Boat: Murray 33-Chouette & Pape Steelmaid-44-Safara-both steel cutters
Posts: 8,492
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Re: Exhaust Plumbing Bypass Stern Squirt
I’ve also seen a muffler setup where the muffler is essentially an air water seperator. I don’t recall details ATM. our big boat has an exceptional Loooong exhaust run and I keep trying to come up with alternatives.
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23-11-2017, 10:33
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#11
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Registered User
Join Date: Feb 2010
Location: East shore Mobile Bay AL
Boat: ODAY 28
Posts: 425
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Re: Exhaust Plumbing Bypass Stern Squirt
I just replaced the mixing elbow on a yanmar 3gm which had the same setup, exhaust water from heat exchange had a T to allow water to go to the mixing elbow and a another hose that sent it overboard. do not think it is a anti siphon valve. maybe a safety to prevent engine from overheating in case the mixing elbow gets clogged which this did. Just thinking here. this was the fist one that I came across that had this setup.
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23-11-2017, 12:49
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#12
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Registered User
Join Date: Jan 2016
Location: Portsmouth, UK
Boat: Westerly Conway 36ft
Posts: 961
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Re: Exhaust Plumbing Bypass Stern Squirt
Its the anti syphon - I have the same on my boat. As previous posters have said, it saves worrying about salt deposits seizing up an anti-syphon valve.
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23-11-2017, 13:00
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#13
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Registered User
Join Date: May 2014
Location: USA
Boat: 41' yawl
Posts: 1,187
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Re: Exhaust Plumbing Bypass Stern Squirt
Quote:
Originally Posted by boeing1
I just replaced the mixing elbow on a yanmar 3gm which had the same setup, exhaust water from heat exchange had a T to allow water to go to the mixing elbow and a another hose that sent it overboard. do not think it is a anti siphon valve. maybe a safety to prevent engine from overheating in case the mixing elbow gets clogged which this did. Just thinking here. this was the fist one that I came across that had this setup.
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No, that was an anti-siphon.
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23-11-2017, 17:05
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#14
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Registered User
Join Date: Sep 2010
Location: San Francisco, CA
Boat: 1980 Pearson 323 - 34ft LOA
Posts: 641
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Re: Exhaust Plumbing Bypass Stern Squirt
Quote:
Originally Posted by boeing1
I just replaced the mixing elbow on a yanmar 3gm which had the same setup, exhaust water from heat exchange had a T to allow water to go to the mixing elbow and a another hose that sent it overboard. do not think it is a anti siphon valve. maybe a safety to prevent engine from overheating in case the mixing elbow gets clogged which this did. Just thinking here. this was the fist one that I came across that had this setup.
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Interesting, I have a 3gm30...
But it definitely seems like the anti siphon. The Yanmar services manual doesn’t show it in its diagram, but the E&M manual shows it.
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23-11-2017, 20:17
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#15
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Registered User
Join Date: Sep 2010
Location: San Francisco, CA
Boat: 1980 Pearson 323 - 34ft LOA
Posts: 641
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Exhaust Plumbing Bypass Stern Squirt
UPDATE: After replacing the mixing elbow the vale/siphon no longer squirts water at idle, and doesn’t shoot as far at higher rpms. My guess is that the elbow was so clogged that it was backing up and out the siphon. Now I wish I had a video for comparison and illustration/reference purposes.
I would post a pic of the old elbow but it looks just like all the other corroded ones on the web
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