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Old 16-08-2016, 16:23   #1
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Wet Exhaust Out Location

Hi i am refitting 35ft steel cruiser, i am moving the exhaust outlet from the stern, due to fuel and water tank placement, the boat has a ford running through a V drive, the motor is on the rear deck and the head of the engine is 400mm above the water line, can anyone see a problem with the exhaust exiting at the starboard side just above the water line
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Old 16-08-2016, 16:44   #2
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Re: wet exhaust out location

Much better than under the swim platform! Bigger issue in my mind is that you have a very large hole in your boat right at the waterline - be sure that water coming in meets as sturdy a barrier as your hull.
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Old 16-08-2016, 18:33   #3
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Re: wet exhaust out location

yes thats what i am concerned about, i were thinking of installing a ball valve inside the hull for when its on the mooring, as the hull is steel the outlet will be welded in not bolted
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Old 17-08-2016, 13:44   #4
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Re: Wet Exhaust Out Location

Exhaust exits the stern is to minimize the fumes. Side exhaust can be blown back aboard. It's also louder.
A lift muffler with a loop will solve the danger of flooding, properly done.
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Old 17-08-2016, 14:14   #5
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Re: Wet Exhaust Outlet Location

thanks Lepke

with the loop, does this need to kept below the height of the exhaust manifold ? or just above the waterline ?
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Old 17-08-2016, 14:24   #6
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Re: Wet Exhaust Out Location

You have to be careful with the wet exhaust almost regardless of where it's placed, due to the possibility of strong waves forcing sea water through it, & towards or into the engine. With obvious consequences. And if the exhaust outlet is under water half of the time or more, when under sail or power, due to being on the side of the hull, then I'm thinking that it's that much more vulnerable.

Some vessels which operate in locales with lots of heavy weather will put a through hull/ball valve at the exhaust's exit at the transom, in addition to a flapper overtop of the exhaust fitting on the boat's outside. And I've even heard of guys putting loop seals into the hose, as close to the exhausts stern exit point as possible, so as to lessen the chances of sea water back flooding the engine.

I may be off on some of the above, as I've far from tried all of those things. Though the idea of getting water shoved into the cylinder head gives me the willies. Especially if the engine can't be shut down in time & the heads get destroyed. Or worse, connecting rods get bent, etc.

The other caveats to one or two of the above techniques is that you need to have a failsafe way of reminding yourself to open the transom's exhaust through hull prior to starting the engine. And also that you can't quickly start up the engine in order to get out of a sticky situation in order to save the boat from harm, or to pick up an MOB, without doing some damage to the engine's ass half plumbing, & also the exhaust system.
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Old 17-08-2016, 15:00   #7
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Re: Wet Exhaust Out Location

I'm guessing (or assuming) that we're dealing with a flat sterned cruiser hull. I guess I also assumed that when you went out the side it was at an angle that sent the exhaust aft. Bad assumption, really. There are plenty of sources to show you how to design a wet exhaust, and how high the loop needs to be. Try Nigle Calder. The problem with out the stern is if that means under the swim platform, a carbon monoxide trap that has killed a lot of swimmers in the water who got under the platform. Personally, I went with a dry exhaust - I don't like big holes at the water line, whatever the number of traps and flaps. A hospital grade muffler is available for any engine that is used as a genset, and others, I imagine.
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Old 17-08-2016, 18:46   #8
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Re: Wet Exhaust Out Location

I work for a boat where the exit is on the stern quarter rather than thru the transom. Dry.

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Old 17-08-2016, 19:13   #9
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Re: Wet Exhaust Out Location

My boat is a sailboat, but has the setup you are enquiring about. Here's my take.

The exhaust isn't louder. I have worried about sea water getting into the motor in a rolling seaway (obviously with the engine off in my case - it's a sailboat!) but this never happens. The loop is simply a big loop of the wet exhaust hose that reaches as high as the underside of the deck. If you add a ball valve to the exhaust, you'll never use it and if you do, you'll forget to open it before starting the engine which will result in the exhaust pressure blowing the exhaust hose off the water lock muffler which will then proceed to spray the engine bay and engine with salt water (don't ask me how I know this!).

Exhaust smells in the cockpit can be a problem when the wind comes from just the right (or wrong!) direction. I think this is due to fact that the exhaust outlet tends not to submerge as much as it would at the rear from squatting and any roll at all keeps the exhaust out of the water for extended times, allowing the gases to immediately be blown downwind which can mean back over the boat.
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Old 18-08-2016, 12:47   #10
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Re: Wet Exhaust Out Location

Any exhaust low and near the stern has the potential to move toward the cockpit, either due to a following wind or the vacuum made by the stern as the boat moves forward. For the most part, that's not a problem - there's not that much exhaust, there's lots of moving air, and all that. I've only seen two situations where there was a real or potential problem. Real- exhaust caught under the swim platform while the boat is immobile - it's killed people. Potential - a lot of canvas over a fly bridge with enough wind/vacuum to be putting exhaust into the tent. If it's a problem, then do what has been done since the first steam ships - up the stack, and let the hot gas loose well above the people. Works every time, with any wind direction.
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Old 19-08-2016, 04:19   #11
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Re: Wet Exhaust Out Location

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Old 19-08-2016, 05:33   #12
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Re: Wet Exhaust Out Location

People dying because engine fumes get caught under the swim platform...humm. I saw that article but I wonder how many of those people were drunk and should not be jumping in the water.

To me those should be counted as alcohol related deaths and not drowning deaths.



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Old 19-08-2016, 17:20   #13
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Re: Wet Exhaust Out Location

Quote:
Originally Posted by GordMay View Post
Yes I like the idea of this
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