Possibly Silly Exhaust Question......

[CaptJake]

Starting to see the light at the end of the tunnel on my "new to me" Najade project (will NEVER understand why, when we get a new boat, we can't just fix what needs fixed we have to INVENT stuff to do!:cussing and I have run into a question I INVENTED and would like to get some input............
After spending the weekend getting the MD2B up and purring I have discovered a leak in the old exhaust thru-hull at the point where the hose clamps to the fitting. Not in itself a major repair but I was wondering about possibly extending the exhaust to exit below the waterline when under power. The way it is setup now it exhausts to air about six inches above the waterline. I have a good drip loop in the hose that attaches to the thru-hull as well as a water trap/backflow preventer at the water injector. No/Little chance of water entering and it is a sound setup(other than the cracked fitting).
My thought process involves adding a 4" extension to the outside of the thru-hull so that at idle it will be easy to verify water flow and the extension will not submerge in reverse. When under power and moving forward only the end of the tube would be submerged to quiet the exhaust a bit and eliminate soot and such.
Any input would be appreciated> Thanks campers!

 

[Bill Roosa]

Be sure to consider heel angles and water that might flow when the boat is sailed with the toerail in the water. That syphon loop may be horizontal on one tack or the other.

 

[kloudie1]

Capt. Jake.. My hunter 34 does what you are talking about.. Exhaust is above water at idle, but the hull squat when underway submerges the outlet.. It is extremely annoying to hear the blub blub blub while under way ..for any amount of time. I am considering a fitting to extend the exhaust out the transom to keep it from going under water. Diesels generate a lot more exhaust gas than gasoline engines at cruising speed, and mine makes big bubbles that are very loud.. It is most annoying when sitting at the helm. I would recommend a temporary rig to test first ..

 

[Patrick S/V Shangra-La]

It will make a quieter exhaust if you place it under waqter....BUT it will also make it inefficient. Because the engine will not be able to exhaust gasses as rapidly as it should. It will cause a severe loss of power. If the engine can not properly breath it will not run to full power, You will end up with black smoke and possibly a hot running engine.

 

[redhead78]

I think you are asking for trouble with the exhaust under the water line. Mine was on the starboard side rite around the water line, I went through considerable cost and extra work to exit the stern above the water line, I am very happy with it, I want to hear the water, exiting the exhaust. Red

 

[Scott T-Bird]

I agree, you don't want your exhaust underwater. Mine does the same as Kloudie at full throttle. But it's not the gurgle that is bothersome to me, it is the exhaust fumes. When cruising along with the exhaust above the waterline, the exhaust is clear and it dissipates behind the boat.

When I inch it forward to full throttle, the boat squats more and the exhaust is submerged. Besides that, the exhaust has more soot and it gurgles to the surface at the stern and seems to cling there. The exhaust actually backdrafts into the cockpit more readily.

I always back off so that the exhaust is above the water line. The air smells so much cleaner, and there is no noticable difference in noise level.

 

[Stu Jackson]

Scott's right, same thing with our boat.

 

[jibes138]

I think it is vitally important to use your senses when out on a passage so that any change in the sound you are hearing immediately alerts you something is wrong. If your raw water system failed you would want to hear a change in the sound of the exhaust to alert you. Exhausting under water may not do that for you.

 

[RAD]

I have the same issue with my boat and it puzzled me that when the boat was under full throttle and squatting if having the exhaust under water was causing back pressure, I do know the since I had the proper pitch on the prop I get very little soot on the transom so maybe all is ok.....If it ain't broke leave it alone?

 

[efhughes3]

I get extreme pleasure when I start the motor up, and see the cooling water spraying out!

 

[CaptJake]

Thanks to all for the input so far..............
The biggest reason in asking the question is that this is the first boat I have owned that exhausted above the waterline (all the other boats I have owned over the years were either I/B's that exhausted below the waterline or "squatted" ,as Kloudie put it, or were O/B's that exhausted through the props.
After a little research today I have found that the muffler has issues (thats putting it mildly). Gonna get a new SS waterlift and put it in place and see if that cures my problem.
I'll keep ya posted.