outboard

[azzo]

Hi,
I have a GIBSEA 242 which is designed to house the outboard in a well.A previous owner moved the OB (which is a YAMAHA 9.9 1984 model) to a mounting hanging on the rear of the boat .I have now put the OB back in the well .However,when I close the seat over the well the engine starts to labour due to lack of oxygen.I guess the exhaust fumes are building up starving the engine of air.The side panel of the well under the seat is open but this does not seem to allow enough air flow.
As this boat is designed to house the OB in the well I find this very strange.
I have thought of connecting a piece of pipe to the exhaust hole to vent the fumes out ?
Has anyone else had this problem ?
Any help appreciated.

Best Regards John

 

[machurley22]

Almost everyone with a two-stroke (I presume it is 2T?) in a well has this problem. I just leave the cover open when motoring but mine lives in a lazarette and this solution is presumably not so convenient if the well cover is a cockpit seat.

Other solutions I have heard of do include a pipe over the exhaust relief. Another is a 12v computer fan rigged to blow fresh air into the well and wired to run when the engine does. Another I have considered (but don't know of anyone who has tried) is a tube to lead fresh air directly to the carburettor.

 

[mainmarine]

I used to have the same problem with a Newbridge Navigator, I had to cut an extra vent in the transom.
Malc
Mainmarine

 

[misterg]

Yes, it is a common problem - The cure is a pipe from the "idle" exhaust to the outside, and to make sure the hole in the bottom of the well is filled in sufficiently to stop the exhaust discharged underwater from bubbling back into the well at idle.

We have a Newbridge Venturer with a similar set-up. As bought, it relied on a continuously operating blower to vent the engine, which drew more current than the engine generated, so flattening batteries (& also made a racket). Tried to duct the exhaust directly to one of the vents, but this gave problems in certain wind directions (notably a gentle following breeze) and turned the inside of the well black. Eventually added a small (10mm??) through-hull. clamped a plate over the "idle" exhaust hole to allow it to be piped (in 1/2" clear pipe) to a tee piece - one leg ends underwater, the other goes to the through-hull No more problems. There were suggestions to pipe the idle exhaust underwater, but I wasn't keen on this, as I understand that it's there to prevent water being drawn back into the engine.

Andy

 

[machurley22]

The advantage of the computer fan (as explained to me) is that it is very low current drain, very quiet (you won't hear it above the engine noise) and very cheap to replace if it succumbs to the marine environment after a season or two.

The exhaust relief valve (as I understand it) is there because the engine does not develop enough exhaust pressure at idle to fully overcome the water pressure to blow the exhaust gases through the prop. The back pressure, if not relieved, makes the engine less efficient at clearing the exhaust gases from the cylinder. Still not a good idea therefore, as you say, to plumb it out under water.

Still haven't explained that very well - hope it makes sense.