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Old 14-07-2016, 02:34   #1
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Do I need a dry riser on my exhaust?

I recently fitted a new engine. It's below below the water line. The exhaust hose goes down to a water block below the engine then curves way up above the water line and down to the skin fitting.

The previous engine never got water in it. I was advised to make a dry riser which I did. It's been a complete nightmare. It has broken and now I am worried it will break again. I would like to remove it but I am equally worried about water in the engine.

Naturally any advice would be great.
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Old 14-07-2016, 03:24   #2
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Re: Do I need a dry riser on my exhaust?

What type of boat?
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Old 14-07-2016, 05:17   #3
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Re: Do I need a dry riser on my exhaust?

If the fall to the water lock is great enough, and the vented loop is high enough, as well as the discharge loop......then no, you don't need a dry riser.


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Old 14-07-2016, 06:15   #4
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Re: Do I need a dry riser on my exhaust?

I truly wouldn't ask here for a good answer. I installed a generator in my boat this year and spent a lot of time thinking about the exhaust system. There are some good articles out there that will address everything you need to know with pictures and diagrams.
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Old 14-07-2016, 09:11   #5
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Re: Do I need a dry riser on my exhaust?

How high is the water line above the exhaust manifold? If a dry exhaust riser is breaking, I would think it's a design flaw or it has to go too high to get above the water line. It would be safer to have a dry riser, but not 100% necessary.

I had a friend that had a 41 ft columbia with an old 4 91 perkins. No riser. the top of the engine was about 6 inches below the water line. he was running with the seas and took water in through the exhaust and got rust on the exhaust valves....did a head job and rerouted the exhaust from the water lock to bring it higher above the water line we also added a flapper to the exhaust exit. Seemed to work for a few years. his health got bad and he sold the boat. It's sat at a dock since. I have only had one riser break and that was due to rust. the boat was in bad repair when I got it. Had the exhaust flange brake on a 40 year old YSM8.

If you hard pipe on the exit side of the mixing elbow you add undue weight and stress to the riser. use hose to the water lock. It should be free standing and as short as possible. it won't need to be very far above the water line. if it's touching anything it will break...eventualy.

good luck
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Old 14-07-2016, 09:33   #6
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Re: Do I need a dry riser on my exhaust?

Quote:
Originally Posted by nixontankgirl View Post
I recently fitted a new engine. It's below below the water line. The exhaust hose goes down to a water block below the engine then curves way up above the water line and down to the skin fitting.

The previous engine never got water in it. I was advised to make a dry riser which I did. It's been a complete nightmare. It has broken and now I am worried it will break again. I would like to remove it but I am equally worried about water in the engine.

Naturally any advice would be great.
I'm dealing with the same thing. I am building a dry riser out of 2" 316 stainless schedule 10 pipe. The bracing is important to avoid vibration fatigue of the metal. Additionally, without the riser, if the water lift muffler can't hold all the water in the exhaust lines when the engine is turned off you can get water in the engine through the exhaust valves. I had to rebuild my engine because of this.

this is the best site for information on this subject I have found:
Everything you Need to Know About Marine Exhaust Systems - Seaboard Marine

hope this helps!
JIm
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Old 14-07-2016, 10:02   #7
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Re: Do I need a dry riser on my exhaust?

You folks are making me feel really good about having chosen a noisy dry exhaust for my boat. I just could not get comfortable with the idea of a 4" diameter hole just above the waterline and well underwater in a following sea. The deck above would have limited the riser height, and we have once been pooped.
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Old 14-07-2016, 10:21   #8
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Re: Do I need a dry riser on my exhaust?

my awesome plastic vetus wet exhaust precedes a lovely 4000 peso piece of exhaust hosing--it is 1000 pesos per meter, 4 meters to go between engine and out ., this keeps out any following sea water, so ..... no added dry exhaust required.
my risers are hoses.
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Old 14-07-2016, 10:44   #9
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Re: Do I need a dry riser on my exhaust?

I installed a dry riser once. The maker put a bellows in it to absorb vibration. Advised. In retrospect I wish I had just put a big loop up in the transom. How far does the exhaust loop above the skin fitting and waterline? I'd want a couple feet.
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Old 14-07-2016, 10:50   #10
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Re: Do I need a dry riser on my exhaust?

We had similar issues getting a riser built and installed properly on our Olympic Adventure 47. Shortly after installing a new Beta Marine 60Hp engine with the stock high rise exhaust elbow, we found water in the oil. No hydrolock or damage done (we were in fresh water at the time) but it but the fear of God in me to make sure it never happened again.

In our case, the long exhaust run and a high loop before exiting the boat meant that there was sufficient water in the line to work its way back into the exhuast manifold in certain conditions. On the windy Columbia river, we would hobby horse quite a bit even in a protected marina and I think we just had water sloshing back to the engine which sits about a foot below the waterline.

The first exhaust riser we had built to correct the issue was too rigid and cracked on our trip from Astoria to the Puget Sound. The repair only lasted a few months longer. finally, I added a flexible coupling and fixed some mounting issues and we have had a successful system for about 150 hours of run time.

Here are a few posts on the travails of our exhaust elbow woes.
http://littlecunningplan.com/2014/07...blues-reprise/
http://littlecunningplan.com/2014/11...ystem-is-a-go/

As tkeithlu suggested, having a dry exhaust would be lovely in many ways. We could have one of the few heated stripper poles in a center cockpit boat.
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Old 14-07-2016, 11:44   #11
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Re: Do I need a dry riser on my exhaust?

Quote:
Originally Posted by nixontankgirl View Post
I recently fitted a new engine. It's below below the water line. The exhaust hose goes down to a water block below the engine then curves way up above the water line and down to the skin fitting.

The previous engine never got water in it. I was advised to make a dry riser which I did. It's been a complete nightmare. It has broken and now I am worried it will break again. I would like to remove it but I am equally worried about water in the engine.

Naturally any advice would be great.
This is one time photos really would help!

From what you are saying I'm guessing it's ok. don't know why it needs a dry riser.

big question is; where is the water injection fitting?

Is it anywhere close to this layout?
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Old 14-07-2016, 18:21   #12
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Re: Do I need a dry riser on my exhaust?

Wow, lots of great info here.

To answer the questions.
The vented loop is 300mm/1ft above the water line

The manifold is 150mm/6 inches below the water line

Exhaust loop is 800mm/32 inches above the water line.

The drop from the manifold to the water block is 250mm/10 inches

The reason it broke was indeed a bad design. That has been rectified. However it's schedule 40 gal pipe and it looks a bit rusty on the outside. I can't imagine how it looks on the inside.
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Old 14-07-2016, 22:20   #13
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Re: Do I need a dry riser on my exhaust?

The diagram provided by DeniseO30 is instructive but omits a key issue in many boats, including ours. With a long run (8 to 10 feet) from the water muffler to the loop plus the column of water that could be standing in the loop itself, you have a lot of water that has the potential to work its way back towards the engine. I suspect this may be more prevalent in larger, center cockpit boats.

When we found water in our engine oil and began our exhaust riser adventures we found an entry from a previous owner's blog that reported a similar condition shortly after launching the freshly painted boat in Mexico. I suspect the water standing between the muffler and the exit loop was able to slosh back to the engine (at that time, a Ford Lehman 75hp).

Of course the other possibility is that an engine that is cranked but does not start allows the raw water pump to fill the lines with insufficient exhaust pressure to expel the water. If the engine does not start promptly always be wary of this condition.
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Old 15-07-2016, 19:29   #14
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Re: Do I need a dry riser on my exhaust?

The diagram from DeniseO30 is great. The important question of how far below the manifold is the water injected into the exhaust was not answered.
If injection is too close to manifold, or not low enough below the level at the exhaust ports (think.. gravity, hobby horsing, etc.), raw water could reach up into the exhaust valves, (rust problem, hydraulic lock).
On some Perkins 4.108, the mixing elbow water injection is just inches away and just below the exhaust manifold. If the aluminum mixing elbow's internal baffle is somewhat corroded, then the water is really close to coming into the engine.
To remedy this, probably can use some threaded, black pipe 45 degree elbows, couplings and nipples threaded to fabricated carbon steel plate flanges on each end, to make a "dry riser" as the original question was asked, (use one pipe size larger than the existing exhaust hose).
Consider this: One of the plate flanges, with a 45 elbow threaded into it, attaches to the exhaust manifold, going up with a pipe for as long as needed ( think water rising, volume of hoses and w.lift muffler, hobby horsing at anchor, etc, not only necessarily above W.L. and not needing a vented loop here) and down again after a second 45 elbow with a pipe of at least 8" long which screws into the second flange which then attaches the original aluminum mixing elbow and raw water nozzle ( need a vented loop on this feed hose) and exhaust hose pointing to water lift muffler. Sort of a 'goose neck' spacer with flanges between the manifold and the mixing elbow.
Of course, must wrap this new pipe and flanges with insulation because this new section is not water cooled and will get very hot there.
Also, should be supported to the engine itself to avoid cracks from engine vibration. Flanges can be reused if ever needed to replace the pipe fittings later since everything is threaded. Use hi-temp. anti-seizing compound when threading things together.
The vented loop for the raw water injection should have some small tubing coming from where the original little valve is, through maybe the exhaust hose's down slope or even better, somewhere just above the water line, outboard, where you can see it.
Maintain the large loop, minimum 12" above the loaded and moving W.L. before exhaust hose exits at the stern and add a flapper valve outboard if concerned.
Slowpoker.
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Old 15-07-2016, 22:56   #15
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Re: Do I need a dry riser on my exhaust?

It's a Volvo penta D2 40.

The water is injected into the exhaust 100mm/4 inches below the water line. The pipe run is quite short. Actually very short.

Also I was unaware that the vented loop was so close to the water line. I had never measured it. That's being rectified and is being brought up to deck level.
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