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Old 03-05-2009, 06:56   #1
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Side Exhaust vs Transom

I am repowering my old Morgan and am thinking of installing the exhaust exit out the stbd side. The engine is under the center cockpit and currently runs about 18 feet to the exhaust throughhull in the transom. When the boat is fully loaded, the transom port is just under the waterline. If I put in the port on the side, how high can I put it? All the info I have says it should be about 3 inches above the waterline. If on the side, heeling will become an issue. If I put the throughhull up to about three feet, it would be out of the water most of the time.

I am doing this for two reasons. First, I have to increase the diameter of the system to accomidate the new engine, and second, I have always been concerned with the exhaust running under the aft bunks. Any feedback?

Steve
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Old 03-05-2009, 08:12   #2
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I am no expert on engines but have been reading a lot on this issue. My engine exhaust is in the center of the stern, 3 inches or so above waterline (never submerges) with one of those rubber flappers to prevent water ingress when slapped by waves on the stern.

My genset exhaust was the subject for my study. I originally had it on the port side but all the way aft, about 2' up from waterline. I changed it to the transom now because I didn't trust it much after seeing what happens around the old position when heeling in a choppy sea.

There are a number of things that are important:

- position of engine: below/above waterline and how much
- position of waterlift muffler: below/above waterline and how much
- distance between top of waterlift and deck.
- distance between exhaust fitting and deck: how high is the loop?

Read up on the subject because I don't even trust most diesel mechanics on this issue.

How many hp is you engine? If it isn't too much, you might be able to use a water separator.

There are also check valves / swan-neck thingies with diagrams and explanations on how to use them, see the Vetus website for examples. These seem to attach to the thru-hull (I have no clue if they are good)

Again, I can't advise you but the above points are what I found while reading. I decided to keep it as simple as possible but did install a water separator and I like it.

ciao!
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Old 03-05-2009, 11:50   #3
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TRANSVERSE EXHAUST SYSTEM:
http://www.cruisersforum.com/gallery...r&imageuser=79

See also:

“Please Don’t Drown Me”
http://www.northern-lights.com/PDFs/...t_drown_me.pdf

From ABYC Section P-01 - Installation of Exhaust Systems for Propulsion and Auxiliary Engines
http://www.cruisersforum.com/gallery...r&imageuser=79

Exhaust System Fundamentals ~ by Dave Gerr
http://www.cruisersforum.com/gallery...r&imageuser=79

Yanmar Exhaust Diagram:
http://www.cruisersforum.com/gallery...r&imageuser=79
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Old 03-05-2009, 12:45   #4
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Mine is about 4" above the waterline aft. You can see it by the car headlight in the picture below.

I have an IOR design so even if I am motoring on a tack the exhaust still comes out of the water once in a while but I don't think the back pressure is any more then the wetlift itself.

If your concerned I'd go with the crossover like what Gord posted. Mine is set up for it but I never reattached it. I used the port side for a whale pump OB (second picture). Besides how often do you motor-sail.

And 3 feet up seems awful high! don't forget when your next to a (fuel) dock or another boat. Where is that exhaust going to go? And a dinghy :-o It's better for it to be directed towards the water just above the waterline.
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Old 03-05-2009, 14:13   #5
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I think what is called the north sea exhaust is what you might consider. I have a center cockpit boat with the exhaust on the starboard side about two feet above the waterline. I don't think it has ever been under water while on a port tack, but it may be possible and scary.
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Old 03-05-2009, 14:39   #6
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Quote:
Originally Posted by kismet View Post
I think what is called the north sea exhaust is what you might consider. I have a center cockpit boat with the exhaust on the starboard side about two feet above the waterline. I don't think it has ever been under water while on a port tack, but it may be possible and scary.
The North Sea Exhaust (Or Transverse or Cross-Over) system should be taken to BOTH sides of the boat, so the windward (high side) exit is always free, even when the leaward exit is submerged.

See the North Sea Exhaust as described in the
Boat Mechanical Systems Handbook by Dave Gerr (page 114):

Boat Mechanical Systems Handbook - Google Book Search
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Old 03-05-2009, 15:26   #7
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The motor in my boat is mounted midships just behind the mast with the exhaust exiting the boat on the starboard side just forward of the mast about three inches above the waterline (boat at rest..).

I am thinking about moving the exaust system so it exits the boat through the transom as murphys law seems to always have the apparent wind blowing a fine spray of cooling water back into the cockpit when motoring - a pain when you wear glasses and for comfort generally.

Always wondered about back pressure when motor sailing on port tack as the exit would seem to be well imersed if we are rail down. Haven't experienced any problems yet though & the boat is 24 years young.

On my old boat the exhaust exited the boat right aft on the starboard side but about 3 inches below the toe rail (made a mess of the topsides as well!) - this was OK but again we would often get the fine spray blown over us. Other boats I haved sailed on with exhausts through the transom dont seem to experience this annoying issue as much.

My first boat had the exhaust exit at the stern but under the transom, the only problem with that was you couldn't easily determine if you had a healthy flow of cooling water.

My .02 cents...
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Old 03-05-2009, 17:03   #8
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On a sail boat where there is the risk of being knocked down I would do everything possible to go with a transom discharge. Unless the boat is quite large side discharges despite loops, etc have a habit of picking up water in a knockdown and flooding back to the engine. I have known a number of boats where they have lost the engine after a knockdown. The problem is worst for dry exhausts.

If using a side discharge (which I would never do myself ) I would go as Gord says but only if the water trap muffler and the loop after it can go in a position that is well above the knocked down waterline.

If you are repowering I assume that the exhaust is wet - if so you have no problems running that through the boat as only very low temperatures are involved (for example, my own wet exhaust is PVC pipe). A vertical rising loop between a good sized water lift muffler (Centek in the US do good ones) and the stern discharge will stop water from following seas driving up the exhaust. It should rise well above the heeled waterlines which is most easily done closeish to the centreline of the boat - it is usually much easier finding a place for a loop in an exhaust running predominantly lengthwise along the boat than if there is a side discharge. You should liaise with the engine manufacturer's agent as to the acceptability of the back pressure on the engine's exhaust from the lift in muffler and loop.

200mm is often given as the minimum distance above the waterline for hull penetrations without seacocks fitted and this is usually, but not always, easy to attain on the transom. I would go for more if possible, especially if your boat tends to squat stern down when under power. If the exhaust goes under water from following waves while motoring there is no real problem from exhaust back pressure.

If done properly there should be no need for any valve or flapper to stop water coming back up the exhaust and if those are considered necessary then I would suggest that you are open to an accident regardless as neither are foolproof.

If you have any doubts whatsoever as to your understanding of the back flooding issues I would recommend that you seek trusted professional assistance.
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Old 03-05-2009, 17:38   #9
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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?

Quote:
Originally Posted by GordMay View Post
The North Sea Exhaust (Or Transverse or Cross-Over) system should be taken to BOTH sides of the boat, so the windward (high side) exit is always free, even when the leaward exit is submerged.

See the North Sea Exhaust as described in the
Boat Mechanical Systems Handbook by Dave Gerr (page 114):

Boat Mechanical Systems Handbook - Google Book Search
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Old 03-05-2009, 17:57   #10
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well, yes, but...

Quote:
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On a sail boat where there is the risk of being knocked down I would do everything possible to go with a transom discharge.
...wouldn't the engine be off if there was enough wind for a knockdown?
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Old 03-05-2009, 18:34   #11
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Quote:
wouldn't the engine be off if there was enough wind for a knockdown?
Pretty much. Ours is a side discharge. It's about 12 inches above the water line. To be that far over the engine wouldn't be running. Any boat can be knocked down and lose the engine performance for about as many reasons as you might dream up. It's pretty easy to say one type of event might be a disaster. In a full knockdown the list of things that could cripple a boat are quite numerous assuming the crew were still aboard.

Given concern about exhaust running under bunks it is running inside the boat. There is the fundamental issue of having an engine inside the boat. It is an inescapable situation. Were there a serious carbon monoxide issue it really wouldn't matter where the exhaust was. Being closer to the the source would not cause death by CO poisoning to be any less dead. Our engine is under the aft bunk.
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Old 03-05-2009, 18:54   #12
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I may have been unclear..I do not have a "north sea" type set-up on my boat. I did have it on an older boat that I owned, when I owned wood boats . Actually, I looked on my own boat and was wrong the outlet is a few inches above the high water line, she is just sitting very high in the water right now.
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Old 03-05-2009, 20:33   #13
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Quote:
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...wouldn't the engine be off if there was enough wind for a knockdown?
Yes, probably so and that likely makes the potential problem worse.

However, most knock downs to mast on water on cruising sail boats are in fact from waves not wind so it is a possibility the engine would be running at the time for propulsion (or charging). If it is running and stays running (which is not an inconceivable expectation in a well found boat) the exhaust flow may in fact help by restricting pick up of water back through the exhaust.

Of course for a side discharging exhaust one could have a valve on it but that assumes the valve is used.

It can happen in ones own backyard so to speak - one boat I know very well with side discharge got within 6 hours of their home port after being away cruising extensively was knocked down and lost their engine through water ingress back through the side discharge. No other problem except for that.

PBlias - A cruising yacht should be able to survive a knock down to mast on the water with nothing except perhaps for superficial damage, after all it is a relatively common occurance for pressed race boats and there is no reason why a well found cruising boat should be any different. This is an objective of the requirements of the ISAF Offshore Regulations for race boats and as also used here as a regulated requirement for offshore cruising vessels to comply with for safety reasons, or as often used as a guide to good practices by others. This is why we strap batteries down, have freezer and refrigerator lids fixed, cooker restrained, locker hatch covers and doors latched, drawers with restraints, etc, etc.
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Old 03-05-2009, 20:53   #14
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with a "norsea" no back preasure
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Old 03-05-2009, 20:54   #15
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I think the name should be rough sea exhaust
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