Exhaust system - SailNet Community
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post #1 of 6 Old 09-18-2018 Thread Starter
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Exhaust system

I think this might be a silly question...but I don't know what I don't know....

Is there any reason the high point of the exhaust (post muffler) to the outlet can't be a shallow slope? I am redoing my exhaust system (and engine, and...) and the existing system goes from muffler, up a bit, over the fuel tank, up further, and to a high point that comes close to straight down to the exhaust thru hull - essentially irregular but shallow slope from muffler to high point, to steep slope to exhaust

I'm thinking of changing the system to a vetus NLP50 that would go up a sharper slope directly to a Vetus NLPG50 and then to a shallow slope to exhaust thru hull.

I don't see a reason moving the steep slope from before the high point to after would matter, but I thought I'd ask. The high point would be very close to the same height and same distance from the center line.

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post #2 of 6 Old 09-19-2018
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Re: Exhaust system

as long as there still is a high point and hose volume between the high point and the engine isnt so much that it can back fill water back to the engine is should be fine

when I researched exhaust for installing my generator I found some great articles on the web, you shoud give a search

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post #3 of 6 Old 09-19-2018
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Re: Exhaust system

I'm pretty sure the water lift muffler (assuming here) should be the only "trap" in the whole line.. the inverted loop and water injection are pretty well established and dependable design elements in Marine exhaust.
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Last edited by deniseO30; 09-19-2018 at 01:58 PM.
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post #4 of 6 Old 09-19-2018
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Re: Exhaust system

' would go up a sharper slope directly to a Vetus NLPG50 and then to a shallow slope to exhaust thru hull.' Con,, A long slope to outlet can allow surging in the hose when stern lifts to following sea and the muffler can only hold so much. Consider a gate valve at the transom and a means of draining the aqua lift. (not necessarily at the bottom) Both good to have ,imo. A loop at the spitting end can reduce ingress from ocean but any water left in hose on shutdown falls to muffler Is it big enough and can you drain it if something fails (Anti s vent?)
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post #5 of 6 Old 09-20-2018
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Re: Exhaust system

Quote:
Originally Posted by reduc View Post
I think this might be a silly question...but I don't know what I don't know....

Is there any reason the high point of the exhaust (post muffler) to the outlet can't be a shallow slope? I am redoing my exhaust system (and engine, and...) and the existing system goes from muffler, up a bit, over the fuel tank, up further, and to a high point that comes close to straight down to the exhaust thru hull - essentially irregular but shallow slope from muffler to high point, to steep slope to exhaust

I'm thinking of changing the system to a vetus NLP50 that would go up a sharper slope directly to a Vetus NLPG50 and then to a shallow slope to exhaust thru hull.

I don't see a reason moving the steep slope from before the high point to after would matter, but I thought I'd ask. The high point would be very close to the same height and same distance from the center line.
I was limited by the cockpit sole and aft deck (my highest point) in my installation. I made sure I installed a waterlift muffler with plenty of volume for the drain back of my 2 3/8" exhaust hose(easy to calculate).

In theory, the exhaust hose could drain back it's entire volume in seawater, at engine shut down.

In practice, I've found surprisingly little seawater (opening the drain to actually see), is in the line at shut down.

The flaw in a system like this is the possibility of cranking the engine so long, you fill the system with seawater. Again in practice, I don't think the battery would hold up long enough to pump the (a very small amount during cranking) amount of seawater needed to fill my oversized waterlift muffler and hose to above the riser, and into the engine.

My exhaust outlet is 12" above the waterline, with the high exit bend in the hose, 12" above that outlet. I'm not worried about backflow into the system. It's worked better than I expected after a couple seasons. My raw water has a vented loop 12+" above the riser which is wrapped in exhaust insulation.

Hope this helps.

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post #6 of 6 Old 09-21-2018
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Re: Exhaust system

Vetus have a formula to calculate the water volume between water trap and high point after the trap. Use this to calculate if the water trap is large enough.
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