Outboard in well, exhaust routing!

[seumask]

We have a Outboard powered Hunter Delta. The outboard is 8 HP 2 stroke Yamaha approx 10-15 years old. There is a significant deterioration in the performance of the engine if we keep the lid on the engine well closed. I belive this is principally due to the high level of exhaust gases in the locker. This Engine exhausts through the prop as well as through two holes near the top of the drive shaft. I want to know if anyone has blocked these holes to make the engine run on the through prop exhaust only and if there are consequences of doing this.

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[tross]

Hi,

I have a Hunter Horizon 23 with the same 8HP twin Yamaha in the well. The outboard was supplied by Hunters pre-modified. Both the exhaust relief holes – the ones at the top of the leg you mentioned, have been plugged by a small length of copper tube. One is pinched off to seal it, the second has a length of clear plastic tubing that tie-wrapped to the leg and emerges 10mm below. the cavitations plate a via a small hole I have cut the bottom of the tube at a 45 angle pointing towards the stern to prevent water travelling up the tube when going forward. I am not sure about the layout of your boat but I added a louvered vent to my locker lid to ensure a supply air to the engine


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[charles_reed]

It\'s a perennial

problem with in-well outboards, that they suffocate themselves.

I'd suggest the only answer is to motor with the well open - i wouldn't recommend blocking any exhaust ports, it might reduce power even further and do little to reduce air starvation.

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[seumask]

Thankyou for the information, I will try this modification, it sounds eminently sensible .I had also been thinking of adding a further vent to the locker to give some sort of cross ventilation. It seemed clear to me that if all the exhaust was below the water line then once moving it was unlikly that the locker would fill up with exhaust fumes as it currently does.

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[misterg]

Hi Seumask(!?)

We have a Newbridge Venturer with an outboard well, and have had the same problem with the engine (Honda 8hp 4st) suffocating. The simplest (and noisiest) answer might be to fit an electric blower to ventilate the well. Other solutions rely on capturing the exhaust & water from these "idle" exhaust ports with some sort of Heath Robinson arrangement and ducting it elsewhere. This assumes that the bottom of the well is sufficiently sealed to avoid the normal exhaust bubbling back into the well at idle.

Some advocate a long tube from the idle exhaust exiting underwater, behind the transom. A string tied to the end allows the tube to be lifted above the water to reduce the back pressure when starting. Personally. I believe that these exaust holes are provided to prevent water being drawn back into the engine, and would be reluctant to compromise this. My current arrangement is a short tube from the idle exhast to a 'T' piece. One arm goes underwater to lose any water expelled from the ports (there will be some, even if it doesn't seem there is). The other arm goes up and ends just inside a vent in the top of the well. This works OK, except with a following wind - when the cockpit fills with the smell of exhaust fumes, and I need to run the blower to keep the engine going. Next step is to add a through-hull above the waterline at the transom to vent the top hose outside the well.

HTH

Andy

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[Joe_Cole]

We had a similar problem; the exhaust fumes kept setting the Carbon monoxide alarm off down below. Apart from it being a nuisance I dread to think what the fumes were doing to SHMBO when she was opting out of sailing.

We put a pipe into the upper exhaust port and led it over board. Problem fixed. Must get round to fitting a proper through hull.

FWIW I was told that the upper exhaust ports shouldn't be blocked as it can sometimes affect tickover and starting.

Joe




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[pft]

We had same problem when we moved from a Yamaha 8 to a Tohatsu 8hp in an Impala well. Tohatsu exhaust came out through prop and also via an exit hole in the leg.
So outboard eventually suffocated itself with the lid on.
Solved problem by inserting appropriately sized rubber pipe into the exit hole in the leg, and taped pipe to the leg so that the open end was under water, but just above prop/cavitation plate.
This cheap and cheerful fix sorts out the problem while in gear and under way, which is when you want the lid on to cut down the noise.
In neutral however the exhaust still bubbles up into the well (from pipe and propeller), but then this is when you are starting, or mooring up so normally not a problem.


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[wiggy]

My brother had an Etap with the same problem so we ran copper/clear pipe from small hole and fed it through transom. Rather than leave lid open how about a vent in the lid.

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[aditi]

Hallo ,i've dealed with the problem over 15 years ago.I owned a hurley 22 in those days and had to remotorise her.I bought a Yamaha 9.9 hp.with in those days a new future the propeller exhoust,but in neutral the gasses bubbled up into the well .which the motor gave not enough air to let it run properly.
We add a little piece of copper pipe and glued it in the upper exhoust.
Drilled a hole in the transom and fitted a hullfitting and a piece of hose inbetween the upper exhoust and the fitting.
The downside of the well we added a rubber seal around the motor to shut the well of for the gasses.
For running the motor propperly an extra vent in the well is recomended.
do it in the transom or so to reduce the noise in the cockpit.
Wishing you a lot of succes to manage the problem ,you can allways mail me to ask about difficulties.

Arthur Leentvaar
Numansdorp Holland

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[oldsaltoz]

G'day Seumask,

And welcome to the forums, you have to add some more info to your profile so we better answer your questions tho'.

I have never owned an outboard in a well, but I did do some repairs for a client who did: he had 2 pipes [Standard PVC cheap plumbers drain type], about 30 mm ID, both thru the hull at the transom, the outboard had a charger built in so he had an in-line blower in the high pipe (any water that entered would drain into the well), and the low pipe was the exhaust air,

Both pipes ran under the cockpit and emerged at the back of the well, the inlet was located at the top and the exhaust about 150 mm below it. None of the pipes were visible as they ran inside a small storage locker built into the rear wall of the well.

The lid and most of the well also had soundproofing material lining the inside.

I hope this helps.

Avagoodweekend....



<hr width=100% size=1> Old Salt Oz /forums/images/icons/cool.gif Growing old is unavoidable. However, growing up is still optional.

 

[seumask]

Re: Outboard in well, exhaust routing solved.

Problem, has now been solved by Zip tying a 1inch diameter tube to the down pipe into which the relife exhaust holes now vents. Tube is approx 20 cm long and stops short of the caviatation plate, and is cut to not scoop water.
In a test last weekend this allows us to motor at 5 to 6 Knots, locker closed( it already has a vent in the transom) with out the normall gradual drop of of performance. The Fumes level is very significantly reduced and you don't get a gush of them when opeing the lid of the locker after running the engine.
Will keep a look out for the potential sucking back up of water.

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