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Old 20-11-2005, 12:34   #1
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New Exhaust Outlet

We have just had a new motor installed in our yacht and the diesel mechanic changed our exhaust set up to a side exhaust. The previous exhaust outlet was low and at the rear of the boat below the boarding platform and was never a high point. It also had a loop in the hose that was well above the level of the outlet. With the new exhaust although it is above the water line, when we sail the boat and it is healing to port the exhaust outlet is now the high point in the exhaust system. Any waves or spray that goes through the outlet will drain down to the motor. It may be ok when healing to starboard as the water would have to go up the hose first to get to the motor. It is when the outlet becomes a high point that is of concern. We regulary cross the Cook Strait in rough seas and with the wind and seas breaking beam on it would not take much water ingress to back fill this hose and flood the motor.
Does anyone else have this problem? Would installing a sea cock near the exhaust outlet that could be easily shut from a locker when sailing in rough weather be the fix?
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Old 20-11-2005, 14:26   #2
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The main thing is that the loop in the exhaust hose always be above the waterline, even while heeling.

I'm assuming you have a Wetlift , and if it's installed properly, this will hold some of the incoming water. After shutting off the motor, wetlifts are still about half full.

The wetlift should be installed a foot or lower then the engine exhaust manifold. And the loop in the outlet hose should be well above the engine exhaust manifold.

My exhaust port is also install on the side about 2" above the waterline.

The other thing to be concerned about is the size of the exhaust. You do not want back pressure. Diesel exhausts are much larger then the norm especially with a wetlift.

Here's a site that deals with exhausts

Torresen
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Old 20-11-2005, 20:57   #3
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Seafox, this could be seriuose or no problem. And I don't think anyone could give you an accurate enough respose when we can't see the situation. I honestly think you should go back to the Mechanic and voice your concern and ask if he has designed this to cope with the situation you describe. If I were the Mechanic, I know I would not be offended, providing the owner was polite of course, and I know I would be happy to show the owner how it would operate safely in a heeled situation. If I couldn't, then I would have to redesgn it. If he say's it will be OK and yet you still feel uncomfortable, ask him to guaranttee his work against such a situation. If he won't, then maybe he has got it right after all.
Good luck
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Old 20-11-2005, 21:28   #4
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delmarrey,
there used to be a loop when the exhaust exit was just above the water line. The boat builder and mechanic have put the new exhaust quite high and there is now no room for a loop. I have a wetlift. I was going to get a bronze seacock or gate to turn off when I sail.

Yes Alan,
we have a few issues with the mechanic. He told me to keep an eye on the exhaust. I could tell he wasn't sure about it. I still reckon a gate or seacock would stop anything going past when we were sailing. When we are motoring there is no problem.

Cheers
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Old 20-11-2005, 21:35   #5
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I will take some photos and post them.
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Old 20-11-2005, 23:38   #6
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Look forward to the photo's. Hmmm, if the guy isn't too sure, I feel nervouse too now. Especially a comment like "keep an eye on it". Mate, that's a worry.
OK, I presume this is a wet exhaust. The first issue, is the engine manifold below sea level at any point of sail?
If no, you can get away with no riser att he engine manifold, BUT, the cooling water must be exhausted into the system in such away, that this water can not run back into the engine. So dropping the exhaust down fromt eh manifold can take care of that part.
If yes to the sea water being higher than the engine, you need to have an exhaust riser fitted from the exit of the manifold as soon as practicle. The exhaust goes up over the riser (on the inside of the pipe of course) and on the downward side, the cooling water is ejected into the exhuast as to ensure exhausted cooling water does not run back down into the engine. This riser (gooseneck) can also have a small valve that allows air to bleed and break any possible vacum that would create a syphon. It depends on installation as to whether that is essential or not, but mostly, it's not needed.
You should also have another gooseneck close to the hull exit. This is to ensure sea water doesn't flood the exhaust pipe and create a back pressure that will make engine starting difficult. Both risers must be above sea level at any point of sail.
I suggest that if your Mechanic hasn't done so, he sorts it out at no cost and tell him to put it down to training to be an expert.
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Old 21-11-2005, 00:51   #7
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Pay attention of the waterline on this drawing

This is the proper installion. Mine is like fig. #2 what is yours?

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Old 21-11-2005, 02:37   #8
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Neither. Best I take some pictures and then try to describe it. Hope to get out to the boat tomorrow afternoon.
The volvo is brand new so if he has cocked it up and water gets into the piston, he will be up for a new motor.
He got us to move the exhaust as the new motor was sooting the transom up quite bad after 2 hrs of motoring. We used to have a 22hp and moved up to a 40hp so with the extra power the transom goes under further and as a result the old exhaust went under water. The mech reckoned it was the back pressure causing the soot. We put the boat back in the water on Sunday and it was so windy and rough we only motored for 20 mins. At this stage there is some new soot (now on the side where the new exhaust is) so we are not too happy.
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Old 21-11-2005, 02:39   #9
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"The first issue, is the engine manifold below sea level at any point of sail?"

I will check to see if it is above or below when I go over tomorrow.

If the motor is installed on the boat centre line and the manifold is above the water line at rest, does it go below the water line when the boat heals. I have drawn some diagrams to try and see but it is a bit confusing.

Also does a riser let exhaust fumes into the boat?
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Old 21-11-2005, 09:20   #10
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Exhaust

I am not a mechanic, but I have been on a few diesel powered boats. I would prefer to have the exhaust go through the transom on a sail boat. The transom does get black soot on it. That happens. You might be able to put a short extension on the exit pipe to move it away. I can also post a copy of my exhaust system as shown in the owners manual. My engine is a Yanmar, the manifold is above the waterline, there is a riser on the back of the manifold, the rubber exhaust goes down to the hull ( inside ) to below water line, into a watertrap / muffler, from there the rubber hose goes up to the transom to a point about 4 inches above the waterline when under full power. The transom drops about six inches under full throttle. I suppose water can go into the pipe with large following waves, but that is what the watertrap / muffler is for, and the riser on the manifold.
I would rather have soot on the transom than a side discharge.
The soot is likely from exhaust fumes that sit in the water, and exhaust that tends to travel with the boat when under a lot of power. I think this may happen more with large transom boats. Do you have a transom hung rudder?
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Old 21-11-2005, 10:42   #11
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The exhaust system shall lead as directly as practicable from the waterlift chamber, to a high point* (riser loop) in the piping, as near to the boat’s centre-line, and as high as practicable.

If a siphon break device is utilized, it should be at the top of the riser loop.

* The high point is sometimes specified at 12 - 18" above resting waterline - but, consult specific manufacturer.

To minimize the backflow of exhaust gasses, into the cockpit or cabin, the exhaust terminus shall be located proximally to the intersection (corner) of the hull side and transom:
~ preferably in the transom, as far outboard as possible.
~ at the extreme aft of a side hull, at the hull transom corner.

For obvious reasons, an exhaust terminus in a side hull, distant from the transom is unacceptable.

I suggest that you discharge this so-called “mechanic”, redo** the work, and backcharge him for the cost. Have everything else he did reviewed by someone competant.

** I presume you'll have a new hole in the side of the hull to deal with. Repairing this would be a "direct consequence" of the installer's incompetance.

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Old 21-11-2005, 11:38   #12
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I won't go any further with the excellent advice given all ready, but I will nudge this thread a little to another aspect. Just how bad is the soot. Is it possible there is some other issue here?? There should be little noticible black smoke. If there is a lot and it is badly sooting up the side of the boat, you have some other issue. And no, exhaust will not be the issue, so if I have understood the excersise correctly, the guy is on the wrong track.
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Old 21-11-2005, 13:32   #13
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This is the exhaust exit. It is 62cm above waterline at rest (2 feet above)

This is where the hose comes from the hull into the boat. There is approx 27cm space above this hose for a loop or inverted U.
It then goes through a panel into the transom locker


This is the transom locker. It then goes down below the waterline to a wet box.


transom locker from above

hose then drops and goes forward to the wet box

and then from wet box up to manifold. Manifold is approx 10cm or 4 inches maybe slightly more above waterline at rest. I am not sure if it goes under waterline when boat heals.

The new engine. Has done 30 hrs. The exhaust was coming out the transom below the boarding platform. There is a transom hung rudder. Everything went very sooty after an hrs motoring. Looked like ****. Polished off a grey colour. No noticeable smoke but a slight unburnt diesel smell. We have only had motor running from travel lift to dock (20mins max) and soot is already starting to appear around new exhaust exit.
My main concern is that the exhaust is installed correctly. When the boat is healing to the exhaust side I think things will be good. It is just when the boat heals the other way and the exhaust exit becomes a high point the waves could slosh water into the exit and it will run down hill to the motor.
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Old 22-11-2005, 04:28   #14
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personally dont like the look of it at all.
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Old 22-11-2005, 04:36   #15
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This looks very ugly, unsafe & unprofessional. Where are you, who was the mechanic/company? I might be able to put you in touch with someone to help out if you are in the South Island.
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