Optimal venturi and bullet placement.

Assuming your putting a new venturi and bullet on a ski, what is the optimal positioning?In my case I need to move a bullet and maybe the Venturi that were not put on correctly causing very very slow bailing. Are there any papers on this? Guidelines to optimize placement for bailing speed and bailing at lower speed.... One in the same?

Bill

On my previous ski (mako6) I put a venturi + bullet from Huki.com. I tried different positions by using silicon (for bathroom). When I found the position I was happy with I glued everything with epoxy. I ended placing the venturi so that the hole that goes trough the hull was the furthest possible from the opening, and leaing a 3mm gap between the venturi and the bullet.

Here are some instructions on how to fit a bullet to Stellar skis. This may help.

Thanks for the suggestions. Hiro, that 3mm measurement is from what to what? Is the 3mm gap in the same space as the paper in JML's pictures? Or somewhere else?

All 3 of my skis have the bullet just inside the scupper and the gap around the scupper and bullet is 5-6mm, they all drain just under 8kph. If you have the bullet too far back the turbulence becomes a factor in slowing down the drainage, which is really the point of fitting the bullets. So looking at the pics in the article I would move the bullet forward 2-3mm from what you see or until you get that 5-6mm gap. These are the instructions I got from my Stellar dealer and how my SEL was delivered.

By my measurements the leading edge of the bullet on the ski in question is 6 mm back from the aft edge of the Venturi. It drains super slow and only over 5.5 mph.

I'm wondering where the best place for the hole is under the Venturi generator is or how far from the tip of the bullet it should be? Is there an optimal placement of the hole under the Venturi hood?

Yeah that bullet will be doing nothing, you will still have turbulence behind the scupper hood, waste of time having it that far back.

www.facebook.com/photo.php?fbid=62191992...51844&type=1&theater

Hopefully you can see this, can't figure out how to post photos to this site.

You should be able to see this.

www.facebook.com/media/set/?set=a.495644...&type=1&l=39a1559b9b

Facebook page won't come up. Might be an iPhone issue.


Oh, works now. Nice faring job. That big flange on Stellar venturis are strange. Seems like a lot of turbulence inducing extra martial.

You can watch my video here:



In my limited experience, the bullet needs to be very close and can even be inside the cone. My "gut" feel was confirmed by my test: it worked best with the cone being of larger diameter than the bullet, with the bullet and cone positioned close enough, so that the area of the opening around the bullet was about the same as the area of the drain tube going into the ski.

Hard to explain, but the idea is simple. You want the bullet close or inside the cone. At the same time, you don't want to restrict/plug the drain - you want to have about the same area open for water to flow out as the narrowest section of your drain. So, if the narrowest cross section of your drain (likely where it goes through the hull) is say 1" square, and if the cross section of your bullet diameter near the drain cover is also 1" square, and if the cross-section of the opening under the widest place of the cone is 2" square, as your bullet is close to or partially inside the cone you will still have about 1" of free space around it even if you have no space front to back between the bullet and the cone. If your bullet is too fat and too close inside the cone, you will restrict the water flow.

If the bullet is too small and/or too far away, you get too much turbulence. If the cone is of the same height as the bullet, then you have little or no speed differential in the water flow over the cone vs. over the bullet, so you have no suction. The bullet needs to be smaller than the cone, at least in the area near the cone.

found a pic

Interesting, it looks like the bullet on your ski Hiro ar quite large. If they were any closer they would rapidly close off the open area behind the venturi. Other smaller bullets go in further for the same open area. Looks like I will just need to mess with it.

In my opinion...The optimal placement is in the bin!

Fit an Andersen Bailer - they work a treat!

And now for something completely different.

It's a one-piece venturi/bullet printed on a 3D printer. It weighs 12g, is 130mm long, 33mm wide, 15mm high and sucks like crazy.

On my Fenn Elite single I now only use one venturi, two is a total overkill.

But the real eye opener was when I put some on my Fenn Elite double and went paddling with a complete novice in the back seat. We were having a social chat and I could hear the venturis sucking air. Anyone who paddles an Elite double will know that the back seat is notoriously wet, to have a bone dry back footwell while chatting with a novice was a revelation.

How do I get one? Or the CAD file to print one? Looks like it would work really well and installation would be fool-proof too.

Oh man... That's super cool! So, how big is the hole it goes over and where does the hole line up on the venturi bullet?

I want one... No, two!

Bill

They are designed to go over a hole up to 20mm in diameter, most drain holes are 15mm or less so they're easy to line up.

Simply remove the old venturi and stick the new one on with superglue. The only way to get it off without damaging the ski is to grind and sand it off again.

They are made in New Zealand, available for NZD20 each. Can do Paypal.

Send an email to oskar at fennkayaks.co.nz if you want some.

Oskar wrote: They are designed to go over a hole up to 20mm in diameter, most drain holes are 15mm or less so they're easy to line up.

Simply remove the old venturi and stick the new one on with superglue. The only way to get it off without damaging the ski is to grind and sand it off again.

They are made in New Zealand, available for NZD20 each. Can do Paypal.

Send an email to oskar at fennkayaks.co.nz if you want some.

Nice work,

Did you do any flow analysis with the CAD to optimise?

Somehow we hit the jackpot on the second chance so didn't need to go there. Nice to have a bit of luck now and then