Bullett - Comparison Test (Video)

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13 years 4 months ago - 13 years 4 months ago #7173 by Kocho
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 ;) 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.
Last edit: 13 years 4 months ago by Kocho.

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13 years 4 months ago #7174 by Tom_D
I built a bullet for my SES that seems to work well. It seems to drain a little faster (nice satisfying sucking sounds) and definitely drains at a slower speed. While your design actually goes up into the drain venturi I rounded the front and had it end just barely entering the drain venturi. All the rest appears similar. Have you tried such a design and if so what were your results.

Great work.

Cheers,
Tom

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13 years 4 months ago - 13 years 4 months ago #7175 by Kocho
Yes, I tried the bullett at several locations and this seemed to work just a hair better than when the bullett was about 1/4" away. Not a big difference and probably other factors would be at play more.

I did another test with a different shape bullet. That seems to work best a little away from the scupper cover.

The version of this video is here (the beginning is the same, added more to the end):
Last edit: 13 years 4 months ago by Kocho.

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13 years 4 months ago #7176 by Tom_D
Thanks for the addition. That bullet looks more like mine with more squared off nose. I rounded the front piece a little more. The SES does have a flat exit so the attachment was simple too (no radius matching). The problem for SES boats is that the cockpit holds A LOT of water. I also added mini-cell foam to take up some of the room behind the foot plate (probably not an option for taller paddlers).

Thanks
Tom

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13 years 4 months ago #7177 by wesley
i put bullets on all my Stellars. At first I had small bullets built by another ski manufacturer that worked pretty good, then I received the much bigger Stellar bullets. I velcroed on 1st bullet placing it about 2/8 inch from drain and that ended up being perfect increasing the draining time by approx 30-35% particularly on decelerating. This made a huge difference in the Stellars since they drain slow any way. Then i placed another bullet too close and it did not work as well so I now have all my bullets about 2/8 inch away. The best draining skis I ever had were my 3 Legends and my Uno. Virtually no water after one stroke!!

Wesley Echols
SurfskiRacing.com
#1 in Surfski Reviews.

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13 years 4 months ago #7178 by Tom_D
I talked to Ed a few months ago about "factory made" bullets. Are they available now? I haven't seen them on the web site.

Cheers,
Tom

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13 years 4 months ago #7179 by Kayaker Greg
They are available here in New Zealand, I fitted one this week. Get the updated rudder too if you don't have one already, makes a huge difference.

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13 years 4 months ago #7182 by Slime
What sort of Legends did you have? I have a glass Legend and it certainly takes more than one stroke to get the speed to empty the cockpit. Or maybe it is my technique.

Cheers

Simon

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