Silent choice system. Single engine. Motor about to go back in. Replacing the transom pipe shutters, but as for Y pipe, wondering if really critical ? Seems everytime I see one, it's at the bottom of the pipe anyways, (broke off). Backing up seems to be only way water could flow upwards, but with single engine it seems not likely. If thru hull is selected, then diverter would be closing off the Y, and if in silent mode, then exhaust pressure would prevent backflow. Opinions??
Thanks

they are their to keep water from backing up into your exhaust system..if your boat is docked and a wave splashes on the back of the boat with out thease it can back up the water as far as the risers then into the engine's cylinders..

I agree about waves and water getting thru tips, but still not convinced that a wave would have any affect of pushing water through the prop exhaust, since it is already a foot below the surface.
I completely understand and fear reversion like the rest, but always thought that those shutters were suspect . The level of water within the y pipe will always be consistent with depth of boat in water, regardless of a shutter or not. They are not watertight. Well, thats my defense anyways.arty-smiley-004

Don't have to be water tight. Just enough to break the inrush

exactly,,the water is already half way up the pipe and when water rush's in the pipe it acts like old faithful..something to consider..for the thirty some bux each its well spent insurance..the reason they fal in the ypipe is usually from running the engine with out water..