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Keysdisease 01-24-2022 02:36 PM

Without any check valves or anti siphon loops any "traditional" lift muffler installation can backflood. The only exception "might" be installations where the generator is mounted way above the waterline. Some of the French catamarans for example have the generators on the bridge deck between the hulls under a cockpit seat.

What Brooksie said is very true. The typical backflood scenario is a vessel tied to a dock when the wind picks up from astern and causes a chop to hit the transom just right and push water up the generator exhaust pipe. Having a lift just slows the flood down as the lift has to fill first. The chop continues to push water up the exhaust until it starts going uphill to the turbo and/or exhaust manifold and then onto the exhaust valves.

Most docks are in protected water and a chop big enough to do this can't build. At anchor your transom is pointing away from the wind or any chop. Typically only in specific conditions like the one described can backflood happen. That's why vessels can go for years with no problem, until the planets align and the rules of fluid dynamics cause water to run uphill and ruin your day.

Transom flappers and check valves can help, making your exhaust run from the lift to the transom as uphill as possible will help. A separator makes it almost impossible. Some people will put a plug in the exhaust when they leave the boat for an extended time, the properly sized inflatable fender works well for this.

:socool:


Quote:

Originally Posted by Cleanslate (Post 1070812)
Ok, interesting. Something is a miss .
Perhaps more rise between the generator and the Aqua lift ( Onan muffler / lift) could have fixed things ?
A new motor in place of the old motor (Perkins? / Onan) won’t solve the hydro lock issues .
I hope all works out .


woodlord 01-24-2022 03:11 PM

That will make exhaust louder above water mine is down just before the bottom
 
[QU=IRENE;1069418]Tom,
Mine is 1 foot below waterline northern lights and very quiet Evan when tied up next to someone on that side
Dana
You probably thought about these already but some pre-caffinated ideas this morning:

Have the yard make the new hole sufficiently high so that the exhaust does not disturb the water. The blowing/bubbling/splashing could be the noisiest thing with your new set (it is with our NL 9kw). The elevated height will work nice with a Gen Sep, if you are going that route.

Take Care,[/QUOTE]

Steve DAntonio 01-24-2022 04:28 PM

ABYC Standards prohibit sharing of exhaust discharges, for obvious reasons, water or gas could migrate into a non-running engine.

Steve DAntonio 01-24-2022 04:35 PM

This doc, from NL, is pretty clear, and better than most other genset and small engine guidance on this subject. https://www.northern-lights.com/medi...t_drown_me.pdf

Alaskan Sea-Duction 01-24-2022 05:36 PM

Quote:

Originally Posted by Steve DAntonio (Post 1071432)
ABYC Standards prohibit sharing of exhaust discharges, for obvious reasons, water or gas could migrate into a non-running engine.

Well I would say this "suggestion" was not around in the 80's, early 90's.

dathompson 01-24-2022 05:40 PM

Quote:

Originally Posted by Ken E. (Post 1069493)
Tom, I also removed an Onan, 6kw, and replaced it with a NL 5kw. Regarding the sound shield, the shop that installed it said that the NL without the shield would be quieter than the Onan with the shield. They were right. And my location is under the salon sole, between the two engines rather than your lazarette location which is farther removed from living spaces. My gen is quiet in the salon and sounds like a sewing machine. We hardly notice it. If you deleted the shield, your access and maintenance would be easier too. I'd spring for upgraded isolation mounts instead, to get rid of any vibration. I'd also go with a separate through-hull for the exhaust and make sure they give you a 1 foot loop above the waterline.

Ken, I run my NL 6kw with the service side panel removed. I can't tell any difference in the noise level.

Alaskan Sea-Duction 01-24-2022 05:42 PM

Quote:

Originally Posted by Steve DAntonio (Post 1071437)
This doc, from NL, is pretty clear, and better than most other genset and small engine guidance on this subject. https://www.northern-lights.com/medi...t_drown_me.pdf

Great point. Great information and coincide with what the mechanic stated. Thanks.

O C Diver 01-24-2022 07:06 PM

Quote:

Originally Posted by Steve DAntonio (Post 1071432)
ABYC Standards prohibit sharing of exhaust discharges, for obvious reasons, water or gas could migrate into a non-running engine.

I've seen a fair number of 40' to 60' sport fishing boats with shared exhausts. We're talking North Carolina
million dollar boats. Many are probably within a foot of the hull in the exhaust tube. My 2002 Cherubini was setup that way but with a side exhaust. Wonder when ABYC came up with that rule.

Ted

Parrothedd 01-24-2022 09:11 PM

Generator exhaust
 
By all means, pay the extra money for the air/water separator. It makes your boat silent in anchorages.

Steve DAntonio 01-25-2022 11:47 AM

Quote:

Originally Posted by Alaskan Sea-Duction (Post 1071468)
Well I would say this "suggestion" was not around in the 80's, early 90's.

I could find out when it was adopted, that's all part of the ABYC Standards record, but I'll agree the proliferation and acceptance of ABYC Standards didn't begin to occur until early 2000s. Still, it's a rarity even on older vessels, and yet I encounter it from time to time even on new vessels.


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