Underwater exhaust

[Hornloaded]

Looked at this boat today.

https://www.yachtworld.com/boats/2000/mckinna-pilothouse-3601563/

It has no mufflers, just underwater water exhaust. I’ve read that this can be an advantage at planning speed because of less back pressure. We will be running this boat at displacement speeds. Would there be any concern about this type of exhaust at the much slower speed.

Thanks
Doug

 

[Al]

In a word: "No". There are cases to be made on the subjct, but as to this boat specific No.

 

[Lepke]

I ran patrol boats with Detroit 6v53s with under water exhaust. Idle, full speed, or anywhere in between it didn't bother the engines. Made them much quieter, too.

 

[Woodstock]

At lower displacement speeds I believe it will exhaust above the water line through other ports.
Ours also has underwater exhaust but doesn't come into play until well into the planing speed range. Until that, the exhaust is through the above water ports.

 

[Arc]

Often there is a high pressure bypass . It is usually a smaller pipe above the water line. Either way not a problem.

 

[Art]

Always have wondered why more boats are not designed having underwater exhausts??

In the 50's/60's there were sweeping right angle exhaust attachments I'd see fitted over transom exhaust pipe. They extended to somewhat underneath the surface of water.

I'd hear pros and cons as to their impacts.

 

[Irish Rambler]

Hi Art. I fitted a s/steel 90' bend on my boat turned outward at a 45' angle for 2 reasons, it does quieten the exhaust a little and more importantly keeps the transom clean from the exhaust soot.
The only other boat I've seen with an underwater exhaust was a Swedish built Coronet boat, very effective but as the exhaust is water cooled there's no visual check for 'tell tale' water so I think it would be wise to fit an exhaust temperature gauge in case of a blocked sea water filter.

 

[Art]

Hi Art. I fitted a s/steel 90' bend on my boat turned outward at a 45' angle for 2 reasons, it does quieten the exhaust a little and more importantly keeps the transom clean from the exhaust soot.
The only other boat I've seen with an underwater exhaust was a Swedish built Coronet boat, very effective but as the exhaust is water cooled there's no visual check for 'tell tale' water so I think it would be wise to fit an exhaust temperature gauge in case of a blocked sea water filter.

For decades... I've always kept rubber exhaust guard flapper on my inboards' exhaust pipe that come out of the stern.

Eliminates the chance of forced backflush into exhaust and enables opportunity to clearly see the flow of cooling raw-water at idle or other RPM.

At idle or just a bit above: This apparatus somewhat decreases exhaust noise... while angling exhaust fumes into the water.

https://autoplicity.com/9053639-sea...MI-qT0oJiK6AIVJh6tBh19UgsIEAQYGiABEgJmlvD_BwE

 

[Ski in NC]

Been on a few McKinna's. I think they use like a 3-4" bypass line that goes to the transom. At low power settings, all the exhaust goes out that line and all is well.

Check that it has the bypass line. I would not want an engine to have to blow its exhaust two feet under water all the time. Makes an annoying gurgling sound like the Volvo IPS, and makes quite a bit of backpressure..

 

[rslifkin]

I think the 45 or 90 degree turnouts that used to be common were mostly for transom soot reduction. One hint in that direction is that they were very common on diesel boats, much less so on gas powered ones.

Personally, I'm not a fan of underwater exhaust or transom (or side) exhausts mounted low enough to be partly submerged. I hate that the bottom edges of mine are underwater with full tanks and a couple of people on board.

It's not exactly a big risk, but if the exhaust outlets aren't clear of the water and you have an exhaust hose failure far enough back in the system, the boat is likely done for. It's not exactly easy to keep up with the inflow from a 5" or larger hole in the boat, even right at or just below the waterline.

 

[tpbrady]

I have an underwater exhaust on the Nordic, but the only thing that goes underwater is the raw water. A muffler does the separation of exhaust gas and water and a second smaller muffler handles the balance and further quiets things down. All you hear at the transom exhaust exiting about 4 in above the water line. At least that is how think it works.

Tom

 

[Hornloaded]

That would explain this horizontal pipe coming off the exhaust.

 

[Cliff Meima]

That is quite a boat for a very good price, in my opinion.

 

[Hornloaded]

That is quite a boat for a very good price, in my opinion.

Actually, the comps are $230 - 250K. Nowhere near 400K. His broker agrees it priced 150K to high. BUC Report places it at 230K. We’ll see if he is ready to come down to reality.

 

[Dubnuh]

Looks like you ended up with her. How's the boat been for you?

 

[Irish Rambler]

Art, those boats are waay above my pay grade, cheaper boat more to spend of the kids inheritance.
rslifkin, maybe just a nod towards the fact that the diesels 'might' be opened up on the pump.
Personally I like to keep it standard and tune the engine/gearbox/propeller for optimum cruising efficiency for speed/economy.
As long as you enjoy your boat then that's great, your boat, your dream come true.

 

[Hornloaded]

Looks like you ended up with her. How's the boat been for you?

Yes, When Covid hit the owner wanted to "Make a deal". I was able to do an engine survey before I made a new offer.245K
Have spent the last 6 months in the slip rehabbing the engines. Internally they are fine, but externally needed all maintenance and corrosion control. Port engine is done and running, Starboard engine should be back on line this weekend.

 

[lwarden]

Looks very nice now. Do you have a before pic?

 

[Hornloaded]

Looks very nice now. Do you have a before pic?

Not the same shot but you can see the general condition. This engine had a leaking salt water pipe for quite some time, so a lot of corrosion to deal with.
Besides stripping and painting, I replaced the After cooler, all hoses, belts and lines, both hydraulic and fuel.

 

[lwarden]

I have to face that on my boat when I get it down south, it's in a similar condition. Can you share the process and materials?

 

[Hornloaded]

I have to face that on my boat when I get it down south, it's in a similar condition. Can you share the process and materials?

I have 6CTA8.3 450HP engines. I have Sea Board Marine (Tony) here at my harbor. He is the Cummins guru locally and on the web.
https://www.sbmar.com
I did everything "Tonys way" That means every bolt has HD marine greese on it. Every hose fitting has rector seal yellow on it. Every water hose has rector seal black sealing it. Turbos were sealed wit red RTV, mounting studs treated with high temp anti-seize.

I used Rust-oleum 2X Ultra Cover® spray paint (gloss white).

I stripped the motors down to the block,head and left the high preassure side of the fuel injection in place. Sanded and cleaned everything. Used DrX rust remover on all rust. I also use DRX for brass on the thru-hulls and sea strainers.



https://drx1.com/


Primed with Rust-Oleum gray primer then painted.
Every part I removed from the engine I stripped to bare steel, treated any rust with DrX and painted with 2X Ultra Cover® spray paint (gloss white).


I replaced every Hose, Belt and hose clamp. Bought new after cooler housings, new Transmission coolers and water pumps. Had the heat ex-changers cleaned and pressure tested.
I added fresh water flush systems to both engines, AC pump and generator.



By leaving the high pressure side of the fuel injection untouched, i just did a normal fuel bleed on the low pressure side and the engine fired right up!


I budgeted $20,000.00 total for both engines and will come in closer to $21,000. That also included making a new exhaust for Starboard engine and custom exhaust blanket.


I'm very pleased with the end results. Both engines look and run like new.
I now have a base line for all future maintenance.

Doug D
2000 McKinna 48PH
New Adventure

 

[Baker]

I have 6CTA8.3 450HP engines. I have Sea Board Marine (Tony) here at my harbor. He is the Cummins guru locally and on the web.
https://www.sbmar.com
I did everything "Tonys way" That means every bolt has HD marine greese on it. Every hose fitting has rector seal yellow on it. Every water hose has rector seal black sealing it. Turbos were sealed wit red RTV, mounting studs treated with high temp anti-seize.

I used Rust-oleum 2X Ultra Cover® spray paint (gloss white).

I stripped the motors down to the block,head and left the high preassure side of the fuel injection in place. Sanded and cleaned everything. Used DrX rust remover on all rust. I also use DRX for brass on the thru-hulls and sea strainers.



https://drx1.com/


Primed with Rust-Oleum gray primer then painted.
Every part I removed from the engine I stripped to bare steel, treated any rust with DrX and painted with 2X Ultra Cover® spray paint (gloss white).


I replaced every Hose, Belt and hose clamp. Bought new after cooler housings, new Transmission coolers and water pumps. Had the heat ex-changers cleaned and pressure tested.
I added fresh water flush systems to both engines, AC pump and generator.



By leaving the high pressure side of the fuel injection untouched, i just did a normal fuel bleed on the low pressure side and the engine fired right up!


I budgeted $20,000.00 total for both engines and will come in closer to $21,000. That also included making a new exhaust for Starboard engine and custom exhaust blanket.


I'm very pleased with the end results. Both engines look and run like new.
I now have a base line for all future maintenance.

Doug D
2000 McKinna 48PH
New Adventure

DUDE.....all of that and no pictures????? Come on man!!!

 

[Baker]

Also, my main engines and generator have underwater exhaust with bypass. The generator exhausts the gas above the water line and the raw water below. It is weirdly quiet and I have forgotten to turn it off on more than one occasion. But that is a good thing ref the quiet. And strangely, the main engines are plumbed the same way except, they are pretty damn loud at idle. They then go full underwater under load. But maneuvering around the dock it sounds like I have 1000hp Detroits. Quiet up on plane and underway.

 

[rslifkin]

DUDE.....all of that and no pictures????? Come on man!!!

He must work like I do. Work, work, work, finish, "oh crap, I was supposed to take pictures"

 

[lwarden]

I have 6CTA8.3 450HP engines. I have Sea Board Marine (Tony) here at my harbor. He is the Cummins guru locally and on the web.
https://www.sbmar.com
I did everything "Tonys way" That means every bolt has HD marine greese on it. Every hose fitting has rector seal yellow on it. Every water hose has rector seal black sealing it. Turbos were sealed wit red RTV, mounting studs treated with high temp anti-seize.

I used Rust-oleum 2X Ultra Cover® spray paint (gloss white).

I stripped the motors down to the block,head and left the high preassure side of the fuel injection in place. Sanded and cleaned everything. Used DrX rust remover on all rust. I also use DRX for brass on the thru-hulls and sea strainers.



https://drx1.com/


Primed with Rust-Oleum gray primer then painted.
Every part I removed from the engine I stripped to bare steel, treated any rust with DrX and painted with 2X Ultra Cover® spray paint (gloss white).


I replaced every Hose, Belt and hose clamp. Bought new after cooler housings, new Transmission coolers and water pumps. Had the heat ex-changers cleaned and pressure tested.
I added fresh water flush systems to both engines, AC pump and generator.



By leaving the high pressure side of the fuel injection untouched, i just did a normal fuel bleed on the low pressure side and the engine fired right up!


I budgeted $20,000.00 total for both engines and will come in closer to $21,000. That also included making a new exhaust for Starboard engine and custom exhaust blanket.


I'm very pleased with the end results. Both engines look and run like new.
I now have a base line for all future maintenance.

Doug D
2000 McKinna 48PH
New Adventure

Thanks for the detailed response. I've read many of Tony's articles and plan to follow most of his suggestions in my rehab project. I hope it comes out half as nice as yours. How did you cope with overspray and fumes in the engine compartment?

 

[Hornloaded]

For overspray, lots of plastic. For fumes I wore a good respirator and kept the blowers on.

 

[KnotYet]

For overspray, lots of plastic. For fumes I wore a good respirator and kept the blowers on.

About 90% of any decent paint job is the prep!