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Old 05-21-2019, 12:09 PM   #1
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Generator Hydro-Locking

So this has happened to me twice now. Sea Conditions were following Seas or off the Port Stern.

Setup:

Genny in cockpit.
Exhaust line is below waterline then enters lift muffler. Top of lift muffler just below water line.

Genny exhaust designed to empty into Port Engine Exhaust.

See schematic.

Solutions:

1. Flapper on main engine exhaust. Problem exhaust tube is 8.5 inches.
2. Install a check valve on top of lift muffler. Exhaust is 2 inches.
3. Install a loop in the exhaust line. Can genny handle this?

I have no way of knowing if this is the original design. When we bought the boat in 03, the generator had new exhaust lines.

I am heading over to Shearwater Marine and see what they come up with, but as always I put forth this issue to my TF brothers.

What say you?
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Old 05-21-2019, 12:31 PM   #2
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I'm certainly not an expert on marine exhaust system but every boat that I've had with the genny in the lazerette had it's own dedicated exhaust with a anti siphon loop after the lift muffler that was well above the waterline... A flapper would be a belt/suspender thing.... Good luck a inop genny can be a show stopper. A lift muffler should have a internal check valve
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Old 05-21-2019, 12:35 PM   #3
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That is a POS genny exhaust system and is guaranteed to back flood the genny. Whoever designed and built this should be shot. Any water that sloshes back into the main exhaust will go into the generator's lift muffler, fill it up and back into the genny engine.



Your best solution would be an exhaust loop as high as possible from the lift muffler before it enters the main engine exhaust. The loop needs to be about 12" above the entry point into the main exhaust line. A flapper on the exhaust hose would also help.


I don't much like check valves although Centek makes them. They can fail and stick open.


And finally what have you done after the two hydrolocks? I would change the oil a couple of times at minimum to get the salt water out of it. If these weren't done then look into the oil filler if it lets you see the exhaust train and look for rust spots on the rockers and springs. If so I would lap the valves.



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Old 05-21-2019, 12:47 PM   #4
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Have never understood why people go to the effort of building a lift muffler into an exhaust system, to only get marginal lift above sea level. My engine lift is over 24" above sea level and the generator which ties into the main engine exhaust tube, has a lift of around 48" above sea level.

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Old 05-21-2019, 12:57 PM   #5
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Sounds to me like the permanent solution is to redesign the muffler system so you get adequate rise above the WL. In your current situation, you may try an exhaust flap and a check valve to try and avoid the problem on this trip. I think it may be a matter of what you can get done in a timely manner, where you are currently, and at what cost. I would imagine that this time of year, most shops and yards are going to be pretty busy.
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Old 05-21-2019, 01:08 PM   #6
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Northern Lights has a good installation manual that clearly defines how to build a safe exhaust system.


https://www.google.com/url?sa=t&rct=...VHGve4SGFNyArh


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Old 05-21-2019, 01:13 PM   #7
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Northern lights also has white paper called ď Donít drown me ď that is a list of doís and doníts for marine exhaust specs.
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Old 05-21-2019, 01:24 PM   #8
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Flapper on the port, main, solution #1, would make it worse IMHO. Don't think of it as the following sea pushing into the genny but rather the port engine exhaust pushing its cooling water into it because it can't escape out the normal route.
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Old 05-21-2019, 01:44 PM   #9
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Quote:
Originally Posted by Alaskan Sea-Duction View Post

Genny exhaust designed to empty into Port Engine Exhaust.

Surveyor should have mentioned ABYC ..... 1.5.7 A separate exhaust system and terminus shall be provided for each engine and generator installation.
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Old 05-21-2019, 03:08 PM   #10
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Originally Posted by Greg S View Post
Flapper on the port, main, solution #1, would make it worse IMHO. Don't think of it as the following sea pushing into the genny but rather the port engine exhaust pushing its cooling water into it because it can't escape out the normal route.



I suspect this is what's happening. You have residual water in the lift muffler. That's normal. In calm seas, your main exhaust is continually blowing it's pipe clear, so not creating back pressure to the gen exhaust.


Now throw in following seas, and your main exhaust is periodically getting submerged. Pressure builds to blow out the water, but that same pressure also pushes back into the gen lift muffler and pushes that water back towards and into the gen. Like Dave says, it's a crap design.


I think the correct fix is to add a dedicated exhaust thruhull for the gen, and be sure there is enough of a loop in the line. The "Don't Drown Me" paper from NL is a good reference.


A shorter term fix would be to install a shutoff valve between the muffler and the gen, or perhaps between the lift muffler outlet and the main exhaust tube. If you put it between the lift and main exhaust, just make sure there is sufficient drop from the gen to the lift muffler so you don't get slosh back into the gen. Placing the valve between the gen and lift muffler would have the most guaranteed results.


The down side of a valve is that you need to be absolutely sure that you re-open it before trying to run the generator, and you need to remember to close it if conditions are the least unsettled. So it's not a good longer term solution, but probably something you could easily get the parts for and implement with minimal disruption to your trip. Then fix it right over the winter.
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Old 05-21-2019, 03:09 PM   #11
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Can you do an elevation drawing (showing a side view) of the same plumbing?
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Old 05-21-2019, 04:03 PM   #12
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Quote:
Originally Posted by kchace View Post
Northern Lights has a good installation manual that clearly defines how to build a safe exhaust system.


https://www.google.com/url?sa=t&rct=...VHGve4SGFNyArh


Ken
Thank you for the reference.

Quote:
Originally Posted by cafesport View Post
Northern lights also has white paper called ď Donít drown me ď that is a list of doís and doníts for marine exhaust specs.
Thank you

Quote:
Originally Posted by Greg S View Post
Flapper on the port, main, solution #1, would make it worse IMHO. Don't think of it as the following sea pushing into the genny but rather the port engine exhaust pushing its cooling water into it because it can't escape out the normal route.
It could, but the main exhaust tube is over 8 inches so I don't think it is coming from the main. This condition has only happened in following seas, so with those and the cooling water from the main, it is possible, but not from just the main exhaust.

Quote:
Originally Posted by boatpoker View Post
Surveyor should have mentioned ABYC ..... 1.5.7 A separate exhaust system and terminus shall be provided for each engine and generator installation.
It might be that this was not a requirement in 1988. Besides ABYC only recommends, it can't require anything.
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Old 05-21-2019, 04:23 PM   #13
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So it would appear I do not have a loop after the lift muffler. I will need to get me some exhaust hose when I get to K-Town.

Thanks Ken for the reference. It helped a lot. My system looks just like the one depicted in the manual, except for the loop.

One nice thing about the genny exhaust emptying into the main exhaust is it is supper quiet.
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Old 05-21-2019, 04:28 PM   #14
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Shearwater should have the loop hose you need and a young agile guy to connect it.
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Old 05-21-2019, 04:55 PM   #15
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Vetus makes a water lock gooseneck that might help.

I gave away a 2" one that I pulled out of my old main exhaust system a few years back to a transient passing through Powell River who had the exact same problem with his generator.

I have a 3" one for my main engine now.
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Old 05-21-2019, 05:42 PM   #16
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The loop will help if the issue is water flooding back from the main exhaust, but I really don't think that's what's happening.


I really think that the same exhaust back pressure that blows the water out of the lift muffler from the genny side, is blowing the water backwards into the genny from the main when the main exhaust goes under water completely from following/quartering seas. The back pressure developed by the main will push equally against the water in the flooded exhaust tube, and against the water in the lift muffler. It will blow the exhaust tube water out the back, and blow the lift muffler water into the generator.
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Old 05-21-2019, 06:24 PM   #17
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Quote:
Originally Posted by twistedtree View Post
The loop will help if the issue is water flooding back from the main exhaust, but I really don't think that's what's happening.


I really think that the same exhaust back pressure that blows the water out of the lift muffler from the genny side, is blowing the water backwards into the genny from the main when the main exhaust goes under water completely from following/quartering seas. The back pressure developed by the main will push equally against the water in the flooded exhaust tube, and against the water in the lift muffler. It will blow the exhaust tube water out the back, and blow the lift muffler water into the generator.



You may be right but the solution is the same: install a high exhaust loop in the generator exhaust and make it exit the transom separately.


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Old 05-21-2019, 06:26 PM   #18
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Yep, never liked exhaust shared between mains and genny. It is done, and some do fine, but get tailpipe submerged or slapped by a wave and the genny (if off) can get a mouthful, more likely than if it had it's own tailpipe. A hump at discharge of water lift is absolutely needed. A foot or two of hump.

I also advise my guys that if you get in rough stuff, just leave genny running. Water won't back up into it running.
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Old 05-21-2019, 07:00 PM   #19
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Thanks everyone for the help. I got a section of hose here at Shearwater, but was only able to raise the hose a couple of inches. According to the NL and my Onan install manual it states the loop needs to be "at lease" 1 foot. I can't get that.

So I ordered one of these and had it shipped to Ketchikan to Frontier Shipping.

https://www.defender.com/product3.js...042&id=1656822
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Old 05-21-2019, 07:21 PM   #20
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Another guide with some reference numbers:

https://www.vetus.com/media/magentom...06234215_0.pdf
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