Video below: comparison of suction of the Epic V10 Sport (2011 model) with and without a custom bullett.
Watch in HD (720p) on YouTube (just click on the YouTube name in the bottom right of the video below).
I first started the test with a bullet that was a little fatter than the one here. It was still smaller than the vent cover but it still did not work well at all - the suction with the bullet was worse than without it.
Then I reduced the dimensions of the bullet to what you see in the video and now there was some improvement: both in the suction force generated as well as in reduced turbulence behind the scupper vent cover.
I might play a bit more with different shapes yet to see if I get any better than this. As it is, adding this bullet increases the force of suction by about 25% (eyeballing it from the higher water level in the clear tube) and visibly reduces the turbulence (by looking at the thread patterns).
Not sure how this translates to in-water performance: have yet to try it. My first test some weeks ago was in the water with a bullet of size and shape that today I saw did not work at all and actually decreased the suction - on the water that same bullet did exactly the same: reduced the effectiveness of the drain. So I am hopeful that my new shape will work better in the water since it works better in the air
![;) ;)](/media/kunena/emoticons/wink.png)
Will see about that soon enough...
There were some other interesting profiles that I think might be tested - for example, adding a sort of "wing" or a "spoiler" over the cover, like on the back of some SUVs or minivans/wagos to direct the flow down and smooth it to increase the local velocity and decrease turbulence.