Aq115100

[brendan]

"hello every one, i am thinkin

"hello every one, i am thinking of running my exhaust directly through the bottom of the boat about 100mm in front of the transom , i would use an inboard pickup scoop facing backwards, my theory is this will cause a venturi to relieve backpressure when the boat is moving but i am not sure if it will idle at rest , has anyone else tried this, the reason i want to do it is to get rid of the noise when the exhaust leaves the water in a port turn and when the boat rolls on waves, other 100 leg owners will know what i am talking about."

 

[sandkicker]

"Its been awhile since I owned

"Its been awhile since I owned one of these, but yes, I know what you mean. What I actually did on mine is the total opposite of what you propose. I removed the exhaust hose from the elbow to the pickup totally with the result of lots more noise but with notably improved performance.

I've done the calculations and the venturi effect is negligable. Its only an improvement vs just being buried, but no net negative pressure, hence any amount of scavanging happens.

What I would suggest would be to:
1) remove the hose from the elbow at the transom to the water pickup/exhausp port.
2) Install a marine muffler inside ( on that long horizontal exhaust run, as far aft as possible.)
3) consider replacing the transom exhaust elbow with a conventional marine exhaust port with a flap.
4) Replace the transom water pickup with at "high speed" raw water pickup about even with the front of the engine. On faster hulls (25 to 30 mph) this seems to give better water flow.
5) Depending on where you boat, install a water strainer and 1/4 turn shut off. I lost an oil cooler on mine whent the cooler got plugged up with "flora"..."

 

[brendan]

"thanks for the reply robert,

"thanks for the reply robert, all good points, the boat performs really well, i am just looking for noise reduction without losing performance, the transom pickup is disconnected, it has a thru hull near the front of the motor."