my underwater exhaust extensions

They are made of hard red rubber and I have the wedges for my curved transom glued onto them.

I looked them up from a patent number and they were in production in the 1960's.
They certainly have lasted the decades well.
Opening measures 5.75 inches. These were cut to sit flush to boat bottom. When new, the down leg was maybe 6 inches longer.

They are unscrewed from hull for some hull work but will go back on. They can grow barnacles on the inside.

I finally found another example on a 1975 Chris Craft on youtube.
Anyone ever seen or have these? I have never seen these on any boats.

These do help with engine fumes.






They show up at the 47 second area on this video
And dont seem to restrict his speed.
https://www.youtube.com/watch?v=6X8bPaIFq1k/

 

Those are vortex generators, they create low pressure that keeps the exhaust gasses underwater a little longer quieting the exhaust. Below is an example of something similar for a larger boat:

 

http://www.fishtheclassic.net/forums/showthread.php?22529-Poor-Man-s-Hooters&
I found another mention of these they show the full size before being fit to a hull.


I only knew what mine were because years ago I looked up the patent number on them. There were 5 pages of installation and how they work.

 

They were mainly to keep the noise down at lower speeds.

 

Here is their patent on the device
https://patents.google.com/patent/US3162171A/en