Idle Exhaust Port Modification

[Plandeck]

Anybody know why it would be wrong to exhaust idle gas from my 8h 2008 4 stroke Nissan outboard through the exhaust plug instead of the regular gas/water mix idle port? Too hot? The idle exhaust must run through 8' of 1/2-inch exhaust hose. (See attached drawing)

Why this? I reinstalled the old 8hp outboard which hung off of the transom into the hold, dropping the prop shaft through the bottom of the boat. So now it is install as if it were an inboard. (see photo) The concern is, dropping it into the hold lowered the power head relative to the water line significantly. The lower unit is caulked where it passes through the hull, but water will obviously enter up the lower unit past the hull. It will enter up to a level somewhere in the middle of the water/gas idle port. Thus it's my preference to exhaust the idel gas a few inches higher through the exhaust plug before it mixes with the cooling water as shown on the drawing.

Any reason why this should not be done?

 

[Sea Rider]

Re: Idle Exhaust Port Modification

Where is the peeing port water flow exiting ? Is it exiting to the engine flooded hull same space ? Where is the exhaust plug located, drawing is shown very small to have a close look. Can you post a pic of that area.

Happy Boating

 

[JB]

Re: Idle Exhaust Port Modification

The exhaust back pressure is essential for smooth idling. Don't mess with it.

 

[TOHATSU GURU]

Re: Idle Exhaust Port Modification

Nothing has changed in the last 8 months...Still a world of not a good idea to screw with the exhaust. While you can gamble with your own life, it is foolhardy to do so with anyone else who might be below deck.

 

[Plandeck]

Re: Idle Exhaust Port Modification

Where is the peeing port water flow exiting ? Is it exiting to the engine flooded hull same space ? Where is the exhaust plug located, drawing is shown very small to have a close look. Can you post a pic of that area.

Happy Boating

Peeing port is seperate and also goes out a rubber hose. Works fine in the boat yard with the lower unit in a bucket of water. (without exceptionally high water line). Attached is photo of motor with different aspects of design noted. For the small size, can you download photo and put it in photoshop for zooming and viewing?

 

[Sea Rider]

Re: Idle Exhaust Port Modification

If it's a still non movable engine, what's the issue of having a long hose exiting from standard idle port to starbord or port side through a upper sea level exit. Is the idle hose exiting just combustion fumes or fumes and water too ?

You have sealed the lower leg to the lower hull area, is it inmaculate sealed to perfection or you have a in/out bed/line of water there. If you deviate the peeing port discharge to a non visible area in case you have a water intake blockage due to algae, floating debris, plastic bags, etc will have big trouble. The peeing port is a visual water indicator showing water pump is working properly and a severe overheat condition could result if not seen.

Love experimenting modifying parts myself too, sorry, but no experience with 4 strokes engines to endorse or not your experiment. Men flew under trial and error...

Happy Boating

 

[Plandeck]

Re: Idle Exhaust Port Modification

If it's a still non movable engine, what's the issue of having a long hose exiting from standard idle port to starbord or port side through a upper sea level exit. Is the idle hose exiting just combustion fumes or fumes and water too ?

You have sealed the lower leg to the lower hull area, is it inmaculate sealed to perfection or you have a in/out bed/line of water there. If you deviate the peeing port discharge to a non visible area in case you have a water intake blockage due to algae, floating debris, plastic bags, etc will have big trouble. The peeing port is a visual water indicator showing water pump is working properly and a severe overheat condition could result if not seen.

Love experimenting modfying parts myself too, sorry, but no experience with 4 strokes engines to endorse or not your experiment. Men flew under trial and error...

Happy Boating

If Idle port is below the water line it will always be filled with water. Then when motor starts up it must exhaust either by blowing out the prop or blowing water out the idle port through 8 feet of exhaust hose to clear the line. The worry is back pressure from water in idle port may make starting/idling difficult.

The main concern with exhausting out exhaust plug a few inches above the idle port is that, although above the water line, it will be a pure gas emission and therefore very hot. May melt the exhaust hose from West Marine which is only rated for 200 degrees. Especially if working very hard in heavy seas. What is your take on this?

 

[pvanv]

Re: Idle Exhaust Port Modification

Hmm... Let's see... If I understand what you were advised not to do last year:

You now have an unrated "inboard" or "saildrive" installation, that is not using USCG Type A1 fuel hose (for starters), and may well not be setup with a proper fuel tank that vents overboard. In addition, you'd like to use exhaust hose that also is not rated for an inboard's dry exhaust temperatures.

Bad plan; Illegal, for one thing; Unsafe for another.

Better check your insurance policy to see whether it will cover you in such a case. And let us all know where your slip is located, so we can stay away from your disaster-waiting-to-happen.

 

[Plandeck]

Re: Idle Exhaust Port Modification

Hmm... Let's see... If I understand what you were advised not to do last year:

You now have an unrated "inboard" or "saildrive" installation, that is not using USCG Type A1 fuel hose (for starters), and may well not be setup with a proper fuel tank that vents overboard. In addition, you'd like to use exhaust hose that also is not rated for an inboard's dry exhaust temperatures.

Bad plan; Illegal, for one thing; Unsafe for another.

Better check your insurance policy to see whether it will cover you in such a case. And let us all know where your slip is located, so we can stay away from your disaster-waiting-to-happen.

I'm using the same outboard fuel tanks that came with the motor. They are mounted under the cockpit seats where they have always been. The fuel lines are the same as came with the motor...they just lead to the inboard rather than the outboard.

Inboards do not have dry exhaust. It seems all boat engins mix the cooling water with the exhaust gas to some extent.

And of course the inboard is now installed with a blower motor to vent any gas accumulation in the bilge.

As far as legality goes...supposedly anybody can still build a boat in their garage and float it without breaking the law. This is different from both cars and houses. If their are other regulations you are aware of I would appreciate a look at them.

 

[TOHATSU GURU]

Re: Idle Exhaust Port Modification

You will be in violation of Federal EPA regulations by altering the emissions.

 

[pvanv]

Re: Idle Exhaust Port Modification

The motor's fuel lines are NOT USCG type A1. They are for above-board use only.
If you add an above-idle-port exhaust, it will be dry.

 

[Plandeck]

Re: Idle Exhaust Port Modification

The motor's fuel lines are NOT USCG type A1. They are for above-board use only.
If you add an above-idle-port exhaust, it will be dry.

Indeed. I did my own test on the exhaust hose from Westmarine putting it up against the manifold of my car to see if it would smoke, smell or burn...negative, it did neither. So I don't see why a dry idle exhaust hose from the above-idle-port plug is a bad idea.

I suppose I could replace the fuel lines with new. Previously the lines ran from the fuel tanks under the cockpit seats (is that above or below board?) out a hole to the outboard motor. What is the difference with USCG type A1? Less chance of cracking and leaking fuel into the hold? Do you feel this important or something to do down the road when the fuel lines in place now start to show wear? They remain visible and accessible their complete length in the new installation. As I've said before we are talking about a 26-foot sail boat, not a liveaboard yacht.

 

[pvanv]

Re: Idle Exhaust Port Modification

Though I advise against the whole design, and have for months, for myriad reasons... it may work for you... but I would prefer not to contribute to it in any way, as I don't want to be liable in the event of a problem.

Any gasoline hoses that are below (not on deck) must only type A-1. Look up the rating definitions for A, B, and C, as well as 1, 2, and 3. The A1 has the least permeability, and the most flame resistance. It has a thick wall. Yes, they would need to be changed to A1 type before deployment of the rig. The same is true of any primer bulbs you plan to use. I believe you also need to delete any quick-connect fittings and replace them with solid, threaded or double-clamped hose-barb type connectors. Otherwise you are in violation of USCG regulations.

Similarly, dry exhaust hose is typically metal, not rubber. Brief field testing is not sufficient. Think about the potential deterioration over weeks or years at those temperatures. Look at an old rubber band to see what I mean. You need hose that is certified for that dry "inboard" application.

And Elvin is correct: you will be modifying the exhaust system, which changes the EPA rating. In theory, you would need to have everything re-certified.

My personal HR-28 sloop has a lazarette-mounted 9.8, but it's based on 1968 USCG regulations for ventilation, mounting, and hoses, because of the age of the vessel, and the outboard is at normal height to the water. In your case, you need to comply with current, 2013 rules, since you are re-purposing the setup. It will be complex and expensive, if you want to do it the "right" way.

For example... Since you are so low to the water... What are your plans for an exhaust riser, that will likely be needed to prevent water from passing through an open exhaust valve and causing liquid lock in a cylinder?

 

[Plandeck]

Re: Idle Exhaust Port Modification

There is a one way check valve just where the exhaust line exits the boat that should prevent water from entering the line. The exhaust line exits the boat well above the water line anyway and is looped on its way to the motor.

 

[pvanv]

Re: Idle Exhaust Port Modification

What will you plan to make the check valve survive the hot gases? Is it metal? How do you plan to service the valve as it accumulates exhaust crud?
How will you keep water from traveling up the "leg" exhaust housing into an open exhaust valve?

 

[Plandeck]

Re: Idle Exhaust Port Modification

What will you plan to make the check valve survive the hot gases? Is it metal? How do you plan to service the valve as it accumulates exhaust crud?
How will you keep water from traveling up the "leg" exhaust housing into an open exhaust valve?

Paul...thank you for taking the time to thoroughly look at my installation. Please see the exhaust installation photos attached. The brass check valve can be opened and serviced from the swim platform.

As far as flooding the exhaust "leg" I'm most concerned about this during heavy healing. Looking at the attached drawing showing a 30-degree heal, which would be a lot. It appears that water would still not travel up the leg. However, in heavy weather with much forward pitching this could be otherwise. If the motor is running the exhaust gas must keep the "leg" clear, no?. Without the motor running only a test in the water will show for sure.

Obviously, this installation is what is called a "prototype". A redesign of the exhaust "leg" must employ a similar check valve as at the exhaust outlet from the swim platform.

There still remains the option of exhausting out the mixed water/gas idle port and capping the dry idle exhaust port. The concern here is that the motor on starting must first clear the exhaust line (blow it out) because the high water line will have partially filled the mixing chamber and probably the exhaust line itself. Too much back pressure for starting? Choice of exhaust port can also be switched after the boat is in the water if one of the two doesn't work, hopefully not at a time the boat is experiencing heavy weather.

 

[pvanv]

Re: Idle Exhaust Port Modification

Many sailboats can get water surge that makes it all the way over the deck (green water on deck), so I would expect that in some heavy weather circumstances, your power head will actually be below the water line. It's not inconceivable to heel to 60 degrees or more (imagine a knockdown, where the spreaders hit the water!)

If you really want to re-invent the wheel, review how inboards are plumbed, with dry exhaust in metal, and then a water injection elbow to cool the gases as they exit the boat. If you divert all of the exhaust before the factory exhaust housing, and then add in a water injection port (possibly fed by the telltale tube)... that might work. Still, I'd advise against the whole project, as there are a ton of engineering items that will require a lot of effort to complete.

 

[Plandeck]

Re: Idle Exhaust Port Modification

Many sailboats can get water surge that makes it all the way over the deck (green water on deck), so I would expect that in some heavy weather circumstances, your power head will actually be below the water line. It's not inconceivable to heel to 60 degrees or more (imagine a knockdown, where the spreaders hit the water!)

If you really want to re-invent the wheel, review how inboards are plumbed, with dry exhaust in metal, and then a water injection elbow to cool the gases as they exit the boat. If you divert all of the exhaust before the factory exhaust housing, and then add in a water injection port (possibly fed by the telltale tube)... that might work. Still, I'd advise against the whole project, as there are a ton of engineering items that will require a lot of effort to complete.

...your concerns are many, but I don't think they relate to my installation only. A knock down will put an outboard mounted on the transom under water just as easily, especially if mounted on the port or starboard side rather than in the transom middle. In heavy weather the motor will likely be running and the exhaust gas will displace water entering up the prop shaft in my installation. Mounted on the transom in heavy weather the prop frequently lifts out of the water and spins. The other disadvantages of transom installation have been ofton debated elsewhere.

One of the best things about my installation is most of the exhaust gas will still exit out the prop. No need for an injection elbow. I think it was Elvin who suggested I "plug the drain holes" and install that way...ie as you seem to be hinting at above. This was the first approach which would produce a dry exhaust only (?), no longer exiting out the prop. But, as best I can remember, I decided against it becuase the possibility of (1) water getting past the lower unit into the middle unit with nowhere to drain and (2) the water pump might not be adequately immersed. (see the attached photo from the discussion with Elvin). Maybe this would be better, but not without re-engineering the connection between the lower and middle units. I felt caulking the joint would not be enough.

As far as my reinventing the wheel...you must conceed there are some cost benefits in what I have done converting from an outboard cantilevered off the transom to an inboard with the motor mounted centrally and lower down where it is most desireable for a sailboat. Installation of an inboard diesel would cost at least fifteen thousand dollars with innumerable problems sourcing a stuffing box to fit a prop shaft etc. Instead moving the outboard to inboard has cost me a couple of hundred bucks!

 

[Sea Rider]

Re: Idle Exhaust Port Modification

Just curious : Is your anticav plate located inside/outside middle hull ? Probably uselees to be outside as the prop will work submerged in deep water to perform well. What about leg oil periodical change ?

Happy Boating

 

[Plandeck]

Re: Idle Exhaust Port Modification

...you see on the attached pictures the penetration of the lower unit throught the hull. The lower unit attaches after the upper unit is mounted through the hull. The gear oil drain plugs are below the hull for easy service. The oil pan must be drained from inside the boat.

...the shift rod presents a problem becuase it passes through the hull without a seal (see photo). I installed a bellows where it exits inside the hull to trap the water and still permit the shift rod to move up and down.