Need explanation of transom thru hulls, please

[Frank Langer]

Hi,

I thought I understood most of my boat systems, but was perplexed yesterday, so would appreciate any help on the hoses going out the transom of our 1984 Ericson 30+. I had to replace two small nylon thru hulls, one of which had a red 5/8" hose attached which came up from the bilge area near the rudder post. The other is a black rubber hose about 1/4" coming from the engine compartment which attached to a bronze nipple and the other part of the bronze piece screwed onto the nylon thru hull. Neither of these is the exhaust hose (which is much larger) or the bilge hose which is also larger. Neither is the fuel tank vent hose, which is separate. Can anyone explain what these two hoses do?

My second question relates to the bronze fitting which is screwed onto the nylon thru hull. I put some lanolin on the thru hull to help this bronze piece thread onto it and tightened it reasonably tight with a wrench, but keeping in mind that I didn't want to break the nylon thru hull. I'm now wondering if I needed to add teflon tape or pipe thread stuff to keep it from leaking. I'm not at the boat to check for leaks--does anyone know if I need to take it apart again or will it likely be ok?

Thanks for any help with this.

Frank

 

[Emerald]

The 1/4" hose is probably from a siphon break on the hot water discharge/exhaust side of your engine's cooling system.

Do you have a little automatic bilge pump in addition to the cockpit mounted gusher hand pump? I remember looking in a side locker once puzzling over a similar size hose, and then remembering the automatic pump which never runs and is out of sight and mind.

 

[Frank Langer]

Thanks, David. I do have an electric bilge pump in addition to the cockpit mounted manual whale gusher pump, and with your prompt, I recall that the hose is red like the one I mentioned, so that's likely it. And your explanation of the 1/4 inch hose makes sense too. So now I'm thinking that it's probably ok to not have used teflon tape on the thruhull for the smaller hose, as there is likely not a constant water flow through that hose, so not much leaking likely to happen there. But if anyone disagrees or has other ideas about this, please let me know.
Thanks again!
Frank

 

[Loren Beach]

The 1/4" hose is probably from a siphon break on the hot water discharge/exhaust side of your engine's cooling system.

And there should be water "peeing" out of that small thruhull any time the Universal diesel engine is running.

Loren

 

[mherrcat]

As noted, there should be water coming out of the 1/4" line when the engine is running. My 30+ has two through hulls for electric bilge pumps; I capped one off when I removed the (illegal) pumps from the engine drip pan. I always check the transom immediately after starting the engine (and regularly when motoring) to make sure there is water coming from the exhaust and the anti-siphon loop output.

I never liked that bronze-to-nylon/Marelon connection. My original nylon through hull became brittle and broke. Part of it remained inside the bronze fitting; nearly impossible to remove. Thought I would just buy a new bronze fitting but found that it was apparently "custom" made and not something that is readily available. Took a lot of heat and scraping to clean it out. I did use some Teflon tape when I remade the connection to a Marelon through hull; should have probably used bronze...

 

[Frank Langer]

I think I'm starting to understand this 1/4" hose. Am I right in thinking that it is connected at the top of the anti-syphon loop and is "peeing" water out when the engine runs because the exhaust is under pressure, so it's going out the main exhaust thru hull, but also being forced out of the 1/4" hose? And then when the engine stops running, water can't get sucked back through the main exhaust hose because the 1/4" line is now empty and breaks the vacuum by allowing air into the anti-syphon loop.

I hope my understanding is correct; if not, please provide additional information so I get it right. I've learned alot about the mechanics of larger boats but obviously am still learning.

Thanks,
Frank

 

[mherrcat]

That is correct. Check the documents section of the site for the E30+ System Plan drawing. It's kind of hard to see, but the engine plumbing drawing shows the anti-siphon loop.

I'll have to try to remember to take a picture of the one on my boat. Just like that bronze fitting on the through hull, it looks like it was cobbled together with plumbing fittings from the local hardware store. It is secured to the underside of the cockpit floor. For the longest time I kept hearing a loud rattling sound when the engine was running and finally tracked it down to the loose anti-siphon loop. I rigged a better, padded, attachment and finally eliminated the rattling.

I need to replace the 1/4" hose because currently it is barely long enough to reach from the anti-siphon loop to the the through hull. I couldn't find a thin 1/4" rubber hose last time I looked.

 

[Frank Langer]

Thanks for your help, Mark,
Frank

 

[chaco]

Stop the Peeing !

Stop the Peeing by putting a Round Check Valve on the 1/4" hose. The only purpose of the hose is to provide a Vacuum Relief to your AntiSiphon so it will Drain. I use the Check Valves on my BlackWater AntiSiphon for obvious reasons. The little oneway B-HOLE on the AntiSiphon Loops fail over time....not good.

 

[Frank Langer]

Dan, what symptoms show that the one way hole on the anti syphon valve is starting to fail? I don't want to replace all the anti syphon valves on the boat, but am wondering if the valve fails, and water is drawn in by the vacuum, the boat could sink. Is there any way to tell if a problem is developing before it gets to this point?
Thanks,
Frank

 

[mherrcat]

Putting a check valve in would certainly stop the "peeing" (and eliminate rust stains on the transom) but how would you know if it was working or not? If it failed and didn't allow air into the anti-siphon loop you could potentially fill your engine up with water, no? (I don't think the boat would sink, but you would have to rebuild your engine!) At least when the through hull is "peeing" I know the anti-siphon vent is clear.

The anti-siphon loop on the exhaust system is not the same as the anti-siphon loops I've seen used in head plumbing; at least mine isn't. There is no one-way valve on the top, just a hose barb to connect the 1/4" hose to the transom through hull. Maybe my anti-siphon is not original equipment? It looks pretty much like what is depicted in the 30+ System Plan drawings.

One thing I did just notice on the System Plan is a check valve in the exhaust line prior to the water lift muffler. I don't think that is in my exhaust system...

 

[mherrcat]

I looked this up in Nigel Calder's book on diesel engines last night. He has several pictures of typical loops you see in head plumbing, so apparently they work, though he says the rubber valves have a tendency to stick.

He says he prefers to remove the valve and run a hose to an above-the-waterline vent. He also mentions that where the hose terminates should be above the highest part of the exhaust system. He recommends somewhere in the cockpit. (?) On my boat that would make it almost at deck level. I guess having it exit that high will keep it from spewing water? I may have to test that...

 

[Glyn Judson]

Loop vent location.

Mark and all, I too had the same dilemma; where to put the vented loop and what make. As with the E30+, I have a traveler on the bridge deck and it's just below there on the inside that I located my Vetus vented loop. You can glue a wood pad there on which to mount the loop. That's about as high as one could reasonably get while still hiding it or any fasteners for it from sight, and it's pretty darned close to the exhaust manifold, making the hose run relatively short. Glyn Judson, E31 hull #55, Marina del Rey CA

 

[mherrcat]

I'm going to try testing the vent hose-above-the-exhaust-system method this weekend. It would be nice to clean the rust streak below that through hull and never have it return. My only concern is that as it stands now, when I see the water spurting out, I KNOW the vent is working; with no water I wouldn't.

 

[EGregerson]

vent

I repowered my e34 last year with a volvo d1-30. The installer put an inverted 'U' vent in line with the raw water intake to the impeller; it's mounted on the engine compartment wall as high as it will go under the cover; (ideally above the motor); he plugged the 1/4" pee-ing line. I don't know why this couldn't be done on the old universal set-up; it would eliminate the long run of hose and potential leakage at the transom thru hull (which i eventually had).

 

[mherrcat]

Maybe I don't understand the physics of the anti-siphon valve, but I was under the impression that these need to be installed on the output side of a pump. When the pump is operating, and creating positive pressure on the output side, the valve is closed, allowing water to flow through the system. On the intake side the pump would be creating negative pressure, sucking in water from the through hull. Wouldn't this negative pressure cause the valve to open and allow air into the system, stopping the flow of water?

 

[EGregerson]

anti siphon

"water can't get sucked back through the main exhaust hose because the 1/4" line is now empty and breaks the vacuum by allowing air into the anti-syphon loop."

I'm not a plumber either. But...I don't think the function is to keep water from coming back into the motor thru the exhaust. I think the objective is to break the flow of water from the raw water intake; the flow stops once air is intoduced whether behind the motor or in front of it. Months after the U (vented loop) (see pic) was installed, the tab on the exhaust thru hull broke off, shooting water into the transom locker; i epoxied it. Everything seems to be working fine; knock on teak.

 

[mherrcat]

This is the exhaust anti-siphon loop in my boat. Looks a little "home-made" doesn't it?

Didn't get a chance to try running the vent line above the highest point in the exhaust hose to see if water still comes out of it. Maybe next weekend...if there's no wind...

 

[EGregerson]

anti siphon

that's what mine looked like with the old Universal 25XP