Exhaust Questions--Extension?

[tbrodes]

Guys,

Was thinking about the boat this morning on a run (finally feeling like spring). My boat has two 4 inch exhausts that are usually above the water line unless I am going offshore to the Gulf stream. about 20% of the time at a moderate cruise speed (20 knots) I get a station wagon effect on the boat (rolling steam back into the cockpit). I was wondering if extending the exhausts past the swim platform would help? In my non engineering mind, I think getting the exhaust out of the vacuum 'zone'. Any idea on a good way to to this? I am half thinking of using exhaust hose and cutting it to extend just past the platform, and securing it to the platform side?

Anyone have construction ideas? tips? Is this the dumbest idea ever?

Cheers

 

[fastjeff]

Somebody makes extensions that put the exhaust under water. That would be a better idea.

Jeff

 

[tbrodes]

Jeff, would there be no issue with the exhaust escaping under water? I have a huge amount of rise between the exhaust and the engines

 

[o2batsea]

I don't think that extending the exhaust is going to do anything more than make the boat look ridiculous. The fact that you are pushing a big box thru the air causes this low pressure area behind the boat, thus the exhaust hanging off the transom. Your only option is to stay away from that area when under way. Engine exhaust is also a big problem on cruise ships. Look at all the wild stack designs...big towers with split outlets that get the exhaust fumes up and over the slipstream of the ship.

 

[Docksidemarineservices]

Relocating your exhaust out the side of the boat mid ship will help with this. Like the Trojan International series boats.

 

[makomark]

Yes, you need to relocate the exhaust outlet outside the 'vacuum zone' to mitigate the backdraft. I doubt extending them further aft will do anything of benefit. Some have had moderate success adding 'elbows' (turnouts) but that will be very hull dependent. Side outlets and 'burying' the outlets seem to be the most effective.

Personally, I'd make some measurements with a sensitive pressure meter to see if the concept will work with your hull. Any fishing buddies in the HVAC arena? They should be able to help with air flow and pressure differential measurements.

 

[knuckle47]

Relocating the exhaust outside of the vacuum zone is the best idea...it worked welll in this design

 

[tbrodes]

thanks guys. I figured I want on to something, but figured i'd ask. Thanks! Only Happens when I go form really warm water to freezing atlantic water until the engines calibrate again.

cheers