Re: Water inversion questions...Vinny?
As I understand it, we are talking about two separate, but related things.<br />With any kind of wet exhaust, reversion is a possibility. It can be brought on by having a big cam, lots of duration and lots of overlap, or by something like a burnt exhaust valve. Anything that could allow the exhaust to be subjected to the vacuum incurred as the piston, having finished its upward exhaust stroke, now starts moving down on the intake stroke. If the exhaust valve is open on the intake stroke [overlap or other fault], then exhaust will also be pulled back into the cylinder. And, since there's water being injected into the exhaust, it'll be pulled in too. It really is only a problem at high vacuum conditions, such as at idle, or when you back off the throttle at speed.<br />A friend of mine who owns a garage told me about the dollar bill test. On a 4 cylinder car, if it has a burnt exhaust valve, or a similar problem, you can hold a dollar bill against the exhaust pipe at idle, and it will actually pulsate in and out. Taller risers, or injecting the water farther away from the engine can help reduce the possibility of reversion. Shutters/flappers wont help for this.<br />As near as I can tell, your static line depends on how low your boat sits in the water. Even tied up at the dock, if you put enough weight in the stern of the boat, the water level is going to rise higher and higher in the exhaust system, even to the point of water spilling over the top of the risers and literally flooding into the engine. This is where shutters/flappers should help.<br />Relentless, I am not familiar with your setup, so I couldn't honestly offer an opinion. It seems to be more of a problem with newer boats, judging by the posts.
<br />There is a measurement called a "static line". What it means is the relation of the water level in the riser's of your exhaust system to the level of the waterline of your boat. If your boat sits too low, or the height of the risers is too short, then the difference between the water you're floating on and the water level in your exhausts is going to be very small. In other words, water could flow back through the exhaust, and into your engine.<br />Vinney likes to also point the finger at engines using roller camshafts, but I've not been able to find any data to back that up. However it is widely recognized that engines that use a camshaft with large amounts of duration and overlap, can cause a reversion condition that can also cause water to be pulled back into the cylinders.<br /><br />I'm sure that Vinney will post here soon, telling me that I don't know squat about roller cams and static lines, and that he's an engineer and he works on boats as a profession, and we're all ignorant, etc., etc., etc.. 
