Outboard Exhaust

[Theis]

What is the exhaust tube fitting? Is that an exhaust tube for the exhaust pressure relief that is on the back of the motor, just under the cowling that tends to fill the laxarette with exhaust fumes? If it is, could you describe it for me?

[Dan Maliszewski]

Exactamundo, Cap. Been in use for several years and works fine. I just found a piece of soft copper tubing whose OD almost matched the ID of the relief port. I think it was 5/16 air conditioner tubing. I carefully tapped it into place with a small plastic mallet and then curved the outside portion up to about the parting line of the housing. From there I use a length of fuel line to a small barbed bronze through-hull in the transom. I use no clamps and just slip the fuel line off the tubing when I raise the motor. Zero fumes in the lazarette and it looks cool too, puffing thru the transom port. The motor is wintering in my shed-I'll post a photo soon.

[Bill]

Outboard exhaust has been the bane of Ariel/Commander sailors since year one. The first edition of the Association's manual had the following: "Outboard motors operating in the confines of the lazarette will frequently choke on their own exhaust gases. One solution for Johnson/Evenrude motors is to attach a length of neoprene hose over the upper exhaust port and tape in place. " Later, a member submitted a better fix using a hose nipple threaded into the exhaust port. Our current Mercury ob has two small exhaust ports in a rectangular protrudance in about the same location. Still trying to figure out a fix for it.

[Mike Goodwin]

My Nissan 4-stroke seems to shoot it all clear of the stern through the prop . I haven't noticed any fumes at all like the Johnson/Evinrude 2-stroke made .

[Bill]

That's one of the 4-stroke's real advantages - underwater exhaust.

[Hull376]

Mike,

I've been thinking about solving the exhaust problem with a 96 Merc 9.8, and after reading this stuff, its clear, if you have the money, go for a four stroke. Bye Bye Merc.

[Dan Maliszewski]

Theis, here is the photo of my outboard exhaust tube as promised. Hope the size comes out ok...

[Dan Maliszewski]

Once again....Evinrude exhaust tube-

[Al Lorman]

My Nissan 5 hp 2 stroke also shoots the exhaust out through the prop.

[Bill]

But, maybe not all of it. If the Nissan, Yamaha, and Merc are all the same engine, then you do have an exhaust relief vent somewhere above the water. The Merc's is on the aft side of the upper shaft about 10 inches from the head.

[Mike Goodwin]

It's Nissan ,Merc and Tohatsu , all built by Tohatsu .

[Bill]

Here's the upper exhaust port on the Mercury et al.

[Bill]

That photo is of a 5 hp 2-cycle. The 4-cylce engines I looked at today all have the same exhaust port.

To eliminate the exhaust gases in the lazarette, I'm thinking a cover with a hose could be placed over the ports to direct the exhaust gases under water. Or, maybe a couple of hose nipples could be tapped into the holes . . but maybe the housing is too thin. Dan's idea of a hose glued into the hole may be the way to go . . .

[Dan Maliszewski]

Bill,
For this engine, you could solder up a copper manifold, using two tight fitting tubes fitted to the motor leg ports, soldered to a horizontal plenum (1/4" tubing) which could be connected to a hose leading to some type of thru-hull fitting. To route the exhaust down the motorleg into the water just lets it boil up back into the lazarette to choke the motor at idle and low speed.

[Theis]

I thank you all. This pretty much answers my concern about where the exhaust was coming from - the alternative being that it was being sucked up from the prop, or from a hole/gasket in the lower unit. My Yamaha has somewhat irregularly shaped square holes. I tapped them for two 1/4" aluminum tubes (I was concerned about corrosion using a dissimilar metal) and they are held in with some compound surrounding the outside.

The reason there is an exhaust problem, from what I have gleaned from Yamaha and various marinas, is that the prop exhaust is some distance, let us say one foot, under the water and that builds a back pressure. At high speed the prop supposedly sucks all the exhaust out (I don't believe that). However, at lower speeds the back pressure from the one foot deep prop prevents the exhaust from escaping through the prop and it must escape through those little holes. If those holes are blocked, the engine gets gunked up, the spark plugs foul, and the motor dies totally unexpectedly after several hours of flawless operation.

So now that I know this is a common problem, I am going to make sure that those holes are ported outside. Thanks for the help.

[Hull376]

Don't know if this could be an issue, but on my 9.8 merc 2 cycle, I noticed that the engine ran rough, lost some power, when my crew bunched up in the back of the cockpit on the way into the dock. Realized that in a following sea, the upper exhaust port on my merc could dunk into the water because of the combination of aft heavy balance and the water welling up. Problem immediately went away when I moved the crew forward, and also by keeping my v-berth water tank full. Bottom line: you might see engine efficiency go way down if you try to run a tube from the exhaust port into the water and thereby introduce backpressure. Comments?

[Theis]

My experience is that you definitely don't want to run the tube in the water (although I saw one boat with an OMC motor that did that). The way I did mine last year does not appear to work The outlet si a couple inches off the water, but for whatever reason, loading, or the wake, or the scoop effect of the well housing, it becomes immersed, although seemingly not by much. Regardless, I am convinced that periodic immersion is what caused so much motor trouble last summer. Now I plan to run the tube out the stern where the outlet will always be out of the water, unless the boat is sinking - then I have a more difficult problem.

[Bill]

Yes, Dan noted above another reason for not running the hose into the water. We had a water routed hose on our last OMC and it worked just fine. The OMC exhaust, however, also included water from the water pump. These functions are seperate on the Merc (water exits from a small tube under the head), which may explain why the system worked on the OMC and not on the Merc, etc.

[Theis]

You have it. The water pump was pushing out the exhaust. My Yamaha just has the exhaust. That answers the question for me why I have never had this problem before. Previously I have had an Evinrude and a McCullough. Thanks.

[Bogle]

Commander #92, La Saladita, came with an OMC outboard and the instruction sheet for a product to convert the above water exhaust port to accept a hose that could be run down into the water!

I was thrilled to find this exists, and then I began looking for it with no luck.

The company is Hansen Machining & Sales, PO Box 336, Antioch, Illinois, 60002, (312) 356-9552. Product is Exhaust Baffle, Hansen Kit No. 12417.

I have searched the internet, made calls, written to outboard repair companies, etc. and found nothing.

Please, let us know if anyone can find some of these.

I like the idea of installing a short tube in the opening of the baffle and then connecting a hose, but the opening size will be diminished and that might affect how the engine runs. Then again, the above water port is only for exhaust relief when the engine is idling. When it runs fast it pushes most of the exhaust out under water. (This is my interpretation, anyway.) If this is the case, there should not be a problem narrowing the above water port a little bit.

I do not think anything short of a fan powered ventilation system will allow the engines to run well with the hatches closed.

Mine runs okay at high speed with the top hatch down, but I leave the forward facing one open, and there is no baffle in the well itself, so air can escape through there.

[Theis]

I live right near Antioch and will drop by on my way to work next week - see if Hansen Machining and Sales still exists and if the product is still offered. Do you have an address, or do you just have the PO Box?

Here is a problem, even with the fan. We all know the exhaust comes out of the back of the lower unit. The air intake is at the tip of the outboard engine hood - I think on all engines - perhaps a foot above the exhaust. What looks like a handle at the back of the hood is in fact the air intake as well.

The exhaust, even when the hood is open, flows upward and passes by the air intake. Leaving the hood open clearly makes a mandatory difference. With the hood open, the exhaust passes right by the air intake on its way out the vents on the top of the hood. But with the hood open, the problem still remains as to how to get the exhaust to exit by the front of the motor well (and not asphyxiate the crew when motoring with a following wind.

[Mike Goodwin]

Why can't the exhaust go out the well down at water level ?

[Bogle]

No, I don't have an address, other than the PO box.

By using Google I found this page:

http://www.gy.com/biz/336399/847.htm

With the following:
Hansen Machining 847-356-9552 23426 W Apollo Ct Lake Villa IL 60046

I have tried calling before with no luck.

Thanks so much for helping me find this part. I had given up.

[Theis]

Bogle:

I'll see what I can do. probably Tuesday.

Mike:

That is what I tried doing this year, and apparently it didn't work. I have a plate around the lower unit of the outboard, to restrict water from coming into the motor well. The exhaust exited through two holes in that plate. When the boat is sitting with no one on board, the outlet is about 6 inches out of the water, pointed straight downward.

The best I can figure is that when there is a crew on the boat, and perhaps when the the boat is moving, the outlet is under water, possibly under pressure from the wake. I had presumed that the exhaust, when the boat is moving would be sucked out, possibly further aided by the passing water, but apparently that isn't so.

One of the problems is that the Ariel moves right along, even when the motor is in idle, or near idle speed. For example, when in harbor, or docking, the motor is not going very fast. The is the very time when there is no exhaust pressure/suction to drive the exhaust through the prop and it has to exit through the the relief ports. When going fast, the wake and backward lean of the boat is maximized so the outlet is closest to or furthest in the water. I have given up on that approach from last year, as a result. I can't affirmatively control what is "out of the water" other than by pushing the exhaust through the transom.

The super clue I received this past year when the fixit shop commented how deep down my prop was (It is a standard long shaft - the prop shaft is about 16" below the waterl), the comment was being made in the context of the exhaust back pressure. That caused me to conclude that the exhaust relief ports might be needed under all conditions.

I have contacted Yamaha and they are useless. I have contacted the dealers and they only question why I have the motor in a well and not hanging over the stern. In other words, dumb and dumber.

[Bogle]

Here are scans of the Exhaust Baffle Instructions

[Bogle]

And Page 2

[Theis]

I went there yesterday morning, and found a machine shop. Hansen hasn't been there in probably 20 years. I called the phone number while there, and no one answered. I did a reverse look up and that was unsuccessful. Two doors down was Hansen Woodworking that had been at this industrial park for more than 20 years, and I thought might be a related. Not so. However he did believe that Larry Hansen of Hansen Marine Products had retired and still lived in Lake Villa. I'll go a little further and see if he is still there and might have a couple of them lying around.

Sorry. A couple decades too late. Another alternative is for you to write the P.O. Box and see if your inquiry is returned. Maybe he uses a P.O. box and works out of his home. Let me know if you are going to do that and keep us posted.

Peter

[Bogle]

I appreciate your efforts, but I doubt Mr. Hansen will have any of these obscure devices laying around. Feel free to call on him, but I do not plan on writing to the PO box.

There are many disused outboards in a shack near my boatyard in Long Island. I'll try to find out if I can scour them for one (ore more) of these. That will not be until spring, however.