Hull Design - exhaust gases from engines through the hull via frets to reduce drag?

[RJA]

Am I correct in thinking that stepped hulls on performance boats are to introduce air between the hull and the water causing less drag? If this is the case is there a hull design that directs exhaust gases from the engines through the bottom of the hull via frets without the need for a step hull.

Balanced headers could easly direct exhaust gases either through the transom at low speed and divert to through the hull as speed increases?

[gonzo]

Stepped hulls have less skin friction. Also, the lift is spread out longitudinally which helps with trim and pitch control.

[RJA]

Would the exhaust if directed through the hull to give a uniform flow provide the same effect?

[magwas]

RJA, the effect depends on the amount of gas put through hull. If there are a lot, then it is called hovercraft. However I think you would need some calculation to see whether (and in which point of the hull) the small positive effect with the exhaust gas compensates for the reduction of power output due to higher pressure the exhaust gas should develop.
A way to ease the pressure requirement would be to form the hull such that the exhaust is in a low pressure point, behind a "riff". But in this case you could even use plain old air.
This way we have arrived very close to a hidrofoil...

[magwas]

I have made a drawing of what I am thinkng of. The vertical part could be equipped with valves, which open when pressure is below ambient air pressure/exhaust pressure.
Anyone have seen a similar thing?
If not, why would it not work?

[latestarter]

This concept seems similar to the Red Bull racing car in Formula One passing the exhaust gases over the rear wing.