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Old 03-05-2009, 22:47   #16
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Originally Posted by akio.kanemoto View Post
I've never seen this before, but the north sea exhaust method looks fantastic.. two questions:

1. are there any disadvantages?

2. is there an issue with the "tee" being almost all the way to port or starboard as opposed to being in the middle?
The problem with the tee being to one side, is if the tee were to be below the waterline on a heel, then it would be no different then just a single exhaust. Once the tee is full the back pressure starts, defeating the purpose of the system.

The other thing that was not mentioned was if the boat was on an opposite tack with the exhaust sticking up in the air. The back pressure of the water trying to run back down the exit hole would be just as bad as if it were submerged. So, either tack is just as bad as the other if the hosing is not configured right.

One of the things I did to avoid that situation was to run the loop from the wetlift as high as allowed then only back down about 6" and back to the transom and then straight down to the exit hole with the maximum amount of bend in the hose. I considered an elbow but that would cause some back pressure. It's like having a tee in the middle w/o the tee. The water can not back up the hose except a couple inches, and on the opposite tack it's still on a downward slope...................._/)
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Old 03-05-2009, 23:55   #17
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I think you missed the point..there is no back preassure with the " north sea" set up, there is always a free opening for the exhaust gas, no matter what side of the boat is a wash..get it?
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Old 04-05-2009, 02:20   #18
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Originally Posted by kismet View Post
... with the " north sea" set up, there is always a free opening for the exhaust gas, no matter what side of the boat is a wash...
An offset common exhaust pipe could place the Tee closer to one side, such that when that side is leaward, the Tee and exhaust may become submerged. Once the Tee is submerged, and fills, the high side exhaust is no longer free & clear.

However, what might not be clear in the previously linked Transverse Exhaust diagram, is that while the engine exhaust & waterlift are indeed offset, the riser hose (should) angles back towards centreline, where it connects to the Tee and transverse pipes (mitigating that concern).
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Old 04-05-2009, 04:54   #19
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...wouldn't the engine be off if there was enough wind for a knockdown?
I can picture heavy seas, running under bare poles with the engine on trying to keep the bow / quarter aligned with the oncoming sea. Knockdown from the seas and not the wind.

But then again, I've not yet had that pleasure.....
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Old 04-05-2009, 10:35   #20
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I can picture heavy seas, running under bare poles with the engine on trying to keep the bow / quarter aligned with the oncoming sea. Knockdown from the seas and not the wind.

But then again, I've not yet had that pleasure.....
Been there, done that. Quite a common experience I suspect.
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Old 04-05-2009, 16:46   #21
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And, of course, one can be in very big breaking seas even when there is no wind - as we were just a few weeks ago departing straight after a storm had quickly abated into no wind at all and so us motoring running before them (that in the direction we wanted to go, wouldn't have departed otherwise ).

But in the end an engine is much more prone to back flooding up the exhaust in heavy conditions when it is not running. Some recommend in such conditions running the engine periodically to help ensure the exhaust system stays unflooded - even though we have a pretty well protected exhaust system (touch wood ) in similar conditions before starting the engine I usually crank the engine a couple of turns with the mechanical fuel stop operated to ensure that we don't have any water logged cyclinders.
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Old 04-05-2009, 19:01   #22
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But in the end an engine is much more prone to back flooding up the exhaust in heavy conditions when it is not running. Some recommend in such conditions running the engine periodically to help ensure the exhaust system stays un-flooded
If it were prone, I think I would be installing a check valve at the exhaust fitting. Which would also work on a system where the tee were to one side, by installing a check exhaust on that side.

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Old 04-05-2009, 21:17   #23
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I usually crank the engine a couple of turns with the mechanical fuel stop operated to ensure that we don't have any water logged cyclinders.
How often would you do that? Would every 5 minutes be enough?
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Old 04-05-2009, 21:39   #24
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side vs transom..

Thank you for the info on the North Sea exhaust - So having read all this, it's quite interesting to note that the original exhaust installation on my boat probably wouldn't have passed muster - the engine is below the WL, the waterlock is below the WL, then there is a 7 to 8 metre winding 1.5m uphill journey to the outlet just under the transom counter about 30 cm above the WL.

I've attached the only pic I have which shows the layout - in the "demolition" phase of the project a while ago (lots of engine access room!). The blue bag in the middle is the engine and the original exhaust hose can be seen just below the port quarterberth.. it doesn't take a direct route as in the pic, (it is just dangling there) - it used to go through the furniture - so add another few metres to what you see in the pic. WL is roughly where the hose enters the bulkhead.

I was originally going to follow the existing install - but with new hose etc - but I'm really thinking that that's not such a good idea anymore.

I thought through the n/e exhaust - and while I love it - there's no real way to get the outlets on each side at the same point and/or without dips etc.. so I'm wondering whether maybe a side-exhaust to port of the engine is the easiest. There is furniture there now and a double bulkhead with about 10-12cm of space in between - can I run a dry exhaust (wrapped/insulated) up to just below deck level inside that bulkhead and inject water at the top (on the downhill side) and have the exhaust outlet just above the WL and be done with it? That way - there's no back pressure and the exhaust run is short etc etc...

Only concern is fire... eek. If the exhaust is wrapped - do you still need space for heat dissipation? It would be touching the bulkheads or be very close.

All suggestions welcome.

Thanks!
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Old 04-05-2009, 23:53   #25
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I usually crank the engine a couple of turns with the mechanical fuel stop operated to ensure that we don't have any water logged cyclinders.

Quote:
Originally Posted by Pblais View Post
How often would you do that? Would every 5 minutes be enough?
Yes, I would be sure that starting the engine every 5 minutes would be plenty for many .

Seriously, I think it depends on your exhaust system and the state of the sea with respect to it, and your experience with ones system in those conditions. To give some context, in our case even in big steep following seas driving against the transom we have experienced no known issues so at worst every 8 hours or so for us. But we have a quite high riser for the boat size in the exhaust system (lifts to 3 foot above the static waterline in a 40 foot boat and is quite close to the boat's centreline so is not lessened by heel and is positioned so we can go down steep waves without tipping water over the top of it), only a 2" dia exhaust and a larger water lift muffler than many.

But for some I am hearing of, I would want to be doing the 5 minute thing .

To give some more context just from our own case, for what that's worth , our bilge pumps exit the transom and the lowest discharge hose has an approx 2 foot rise above the static waterline (I have not measured it and it is affected to some extent by heel as it is a bit more outboard from the centreline of the boat) and has a plastic non return valve in it - in heavy conditions we sometimes get some water back through that, I assume due to motion flapping the non return valve flap as in the application there is not a constant head on it to keep it closed.
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Old 05-05-2009, 05:16   #26
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You can insert a valve between the loop and muffler. Just be sure to open it before you light off the engine.
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Old 05-05-2009, 05:43   #27
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Quote:
in our case even in big steep following seas driving against the transom we have experienced no known issues so at worst every 8 hours or so for us. But we have a quite high riser for the boat size in the exhaust system (lifts to 3 foot above the static waterline in a 40 foot boat and is quite close to the boat's centerline so is not lessened by heel and is positioned so we can go down steep waves without tipping water over the top of it), only a 2" dia exhaust and a larger water lift muffler than many.
Our lift rises above the waterline and exits from a 2 inch exhaust opening. It;'s clearly 8 ft shorter going out the side. We can't exit straight back on the transom. It's not in the center of the boat but even with the doghouse. It's about 20 inches above the water. We have quite a long cockpit. Even though we have not been on it most of the miles it has been up and down both US coasts and Caribbean. It's seen a lot of seriously bad weather. In a broach it could be a problem but I think in cases like that it's not the worst problem to deal with or that the orientation of the exhaust is the issue. I do like it since I can see it spitting water from the helm. It shoots out a fair bit. A submerged exhaust has all the same orientation relative to the boat. I like the flap idea though. You do see it on much larger engines.

Our bilge exits to the rear and quite high. The transom is angled enough that it does not dribble down. It means there is always a column of water that remains in there. Under low pressure the check valve leaks backward a bit.
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Old 05-05-2009, 18:52   #28
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Our exhaust is 3" and that is the minimum size for the flappers available. For our 2" genset exhaust, I'm buying a short piece of fiberglass exhaust pipe (Centek makes that) so I can cut a 2" piece of that and epoxy it on the transom over the 2" thru-hull. After that, I can fit a flapper on there as well.

Like another poster wrote: these flappers are not 100% closed but they effectively block the momentum during a surge, so they are really nice indeed.

About the water separator: we have the Centek "GenSep" thingy on the generator. It replaces the loop between waterlift muffler and thru-hull. The nice thing is that if water backs up through the exhaust, this is the first place it ends up and it will just drain out of it through it's standard water drain. Only when the surge is big enough to fill the gensep up, some water will go down into the waterlift muffler... the rest will drain out overboard.

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Old 20-01-2010, 02:50   #29
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tartan 34c have standpipes they are soldered up with the exhaust pipe inside a larger pipe. jacketed sort of. the water is injectednear the top and the water and exhaust exit at the bottom
I have read praise about this system (in my 34) for the "water cant flood the engine. but the exhaust pipe is run from engine to standpipe hot-too hoy for me nomatter how much insulation i apply the nearby boat gets very hot
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Old 20-01-2010, 09:16   #30
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tartan 34c have standpipes they are soldered up with the exhaust pipe inside a larger pipe. jacketed sort of. the water is injectednear the top and the water and exhaust exit at the bottom
I have read praise about this system (in my 34) for the "water cant flood the engine. but the exhaust pipe is run from engine to standpipe hot-too hoy for me nomatter how much insulation i apply the nearby boat gets very hot
If its like what I have seen the problem is that there is no way to monitor the condition of the internal pipe and if it develops a crack inside it will flood the engine.

I went with a dry riser as the highest point in my system,,,the water is injected after the bend around a sleeve inside, then the wet exhaust goes down to the water lift, then up to a loop that’s 8 inches lower than the top of the dry riser, then slopes down/runs aft to the hull exit about 3 inches above the WL.
My engine is new so generally fires right up...but if there was a problem and it was over cranked...the water would exit the exhaust and not go back into the engine because the dry riser is so high.

This was all done in part to not void my engine warranty...I was limited by the maximum height I could have from the bottom of the pick-up pipe in my water lift chamber, to the loop before the exhaust exits.
In other words the maximum height the exhaust gas would have to push the water out, that translates to back pressure.
I also went to a bit of trouble to isolate all the exhaust components from the hull and other parts of the boat...this is said to reduce the exhaust noise quit a bit.
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