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post #11 of 32 Old 10-29-2018
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Re: Exhaust under water

Here's a video of my boat doing the squat thing. And my exhaust dips below water at times

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post #12 of 32 Old 10-30-2018
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Re: Exhaust under water

My boat squats at higher engine speeds but not under sail. The difference has to do with the engine pushing the boat vs. the sails pulling the boat, like jtsailjt said.
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post #13 of 32 Old 10-31-2018
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Re: Exhaust under water

Hopefully you have a loop significantly above the waterline with a vacuum break to prevent filling the exhaust and then the engine. The most important time to not have water in your exhaust is before you start the engine. Back pressure then burns out starters. Some will need to tack to drain exhaust before starting engine to prevent this and then drop sails as they come in. The run from through hull should go straight up to top of loop to prevent this occurrence thereby eliminating need to worry about back pressure ruining your starter. Some boat have such funny runs closing the through hull is necessary whenever the engine isnít running. My prior genset was like that. The one Iím putting in isnít.
Some diesels will tolerate a bit of back pressure but decreasing or eliminating it is a good thing from what I understand.

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post #14 of 32 Old 10-31-2018
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Re: Exhaust under water

Tens of millions of powerboats with exhaust exiting under water. Most (not all) outboards exhaust under water.
My 55hp diesel exhausts under water. My previous 235hp diesel exhausted under water. My 145hp Perkins did 20,000hrs exhausting under water before I rebuilt her ..... maybe she would have done 40,000 if she'd exhausted above water

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post #15 of 32 Old 10-31-2018
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Re: Exhaust under water

Stinkpot exhausts are typically engineered below the waterline, with proper diameter, etc. The OP’s was reportedly design above. Adding resistance underwater, for an exhaust that is above the waterline to begin with, could be significant. Bends in the run, as well as exhaust diameter matter, so I’m sure blocking the exit with water is too.


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post #16 of 32 Old 10-31-2018
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Re: Exhaust under water

I'm asking as much as informing, but...
When you push or pull anything through water, isn't there a vacuum right against the trailing surface? In the case of an exhaust, I don't think there would actually be any water at the exit, and therefore no backpressure at all. What do others think, or know?
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post #17 of 32 Old 11-01-2018 Thread Starter
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Re: Exhaust under water

One problem with the exhaust under water, cant see water flow or hear the hollow sound of no water flow.
Thanks for all the replies, I think all is normal so one less thing to fixate on.
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post #18 of 32 Old 11-01-2018
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Re: Exhaust under water

Quote:
Originally Posted by thumper53 View Post
One problem with the exhaust under water, cant see water flow or hear the hollow sound of no water flow.
Thanks for all the replies, I think all is normal so one less thing to fixate on.
I agree, all normal and nothing to worry about however, a raw water flow detector/alarm is a wise investment. It has been the first thing added to each of my boats.
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post #19 of 32 Old 11-01-2018
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Re: Exhaust under water

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Originally Posted by boatpoker View Post
I agree, all normal and nothing to worry about however, a raw water flow detector/alarm is a wise investment. It has been the first thing added to each of my boats.
Or an exhaust temperature alarm which is what I installed.
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post #20 of 32 Old 11-01-2018
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Re: Exhaust under water

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Originally Posted by MastUndSchotbruch View Post
Or an exhaust temperature alarm which is what I installed.
The advantage of the raw water detector is that it alarms the instant there is loss of flow. You may already have a fried impeller by the time an exhaust temp alarm goes off. It does not hurt to have both.

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