idle exhaust port under water?

Tohatsu Guru,

I know you won't recommend I do this, but is it possible to do it without harming my Tohatsu MD40? It's a short shaft and doesn't fit the transom of the boat that I have. I could cut the transom to get the anti-ventilation plate at the correct level, but then it looks like (from the water level stain on the hull of the boat), the idle exhaust port is going to be one or two inches under water at idle.

What if I somehow attach an exhaust tube to the idle exhaust port, angled upward breaking the surface of the water? Would the water that comes out of the port get backed up in the tube and cause too much backpressure or somehow enter the combustion chambers? The outboard that my MD40 is replacing on this 15ft bass boat was a 85hp Johnson with PT+T - 300 lbs compared to 140 lbs now so maybe the boat will sit higher in the water at idle I don't know yet. If so, and the port is out of the water, how high out of the water should the port be? Thanks.

Is the boat in " good shape " or is it waterlogged. -------------------------Many old boats have " foam flotation " that over the years have soaked up a lot of water.

racerone,

Thanks for pointing that out, it didn't cross my mind. Yes it is an old boat and had 8-10 inch waterlogged foam under the entire deck. The fiberglass covered plywood deck was rotten and I have already replaced it with plywood and epoxy paint. I tore out all of the heavy waterlogged foam, so that combined with a lot lighter outboard ought to make the boat ride higher in the water now. I did that work about 2 months ago and wasn't thinking about that.

Still though, the idle exhaust port is going to be close to the water or under it a little since I have to cut the transom to get the anti-ventilation plate low enough - the boat was made for an outboard with a 20 inch shaft. I know that getting the boat in the water and marking the transom at the water line is the thing to do. Just wanted to know beforehand if my idea of an exhaust tube (if I can figure a way) would possibly cause the cooling water that comes out the idle exhaust port to back up in it and hurt the engine or it's performance, and the minimum height the idle exhaust port can be above the water. Thanks.

The idle exhaust relief can be just above the waterline.----------------Just make sure the motor is tilted up when launching / retrieving / not running.

racerone, thank you.