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PostPosted: Fri Jul 15, 2011 6:32 pm 
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Joined: Sat Nov 12, 2005 10:46 pm
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Location: Escondido
Thanks stringy. It turns out that I didn't have as clean of fit in the scupper as it appeared. On my boat the top and bottom of the scupper halves are misaligned just enough to break the valve off. A smaller valve is needed to get a clean fit -- one that can be adopted to fit inside the scupper cap would be ideal. This could also be a floating ball valve.

For newer members, any kind of tape works for the venturi slot, but a clear packaging tape leaves no residue, has minimal stretch and good drag characteristics. In comparing tapes, the premium tapes last longer -- at least a couple of months if you're careful. Differences are small, so whatever you have around is fine. If you're going out to get some, 3M Scotch 3850 has the best adhesion and tensile strength, but Hinkle (Locktite) HP260 gives a lot of bang for the buck IMO. I use both.
Image

For kayaking, you can also tape up the daggerboard well (AI) (keep the venturi slot) to eliminate water intrusion and improve speed. You can insert the board right through the tape any time. Taping the centerboard well on the TI while kayaking also improves speed. 8)


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PostPosted: Tue Aug 02, 2011 3:17 pm 
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Joined: Tue May 18, 2010 2:31 pm
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Location: Kailua 96734
Sorry guys, I am missing something here.

I was under the impression that all scupper holes have a built-in Bernoulli effect of their own, hence one reason they are found on kayaks. While in motion, the Bernoulli vacuum pulls water from the cockpit.

So why tape the scuppers? If a larger wing area creates more lift, would not a larger scupper (and more speed) draw water more efficiently?

Or are we talking a "venturi" effect here, where narrowing an opening creates an acceleration of air/fluid which is already under pressure? Sort of like my snoring. :mrgreen:

Please set me straight.

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"THE WIND IS YOUR FRIEND,.."


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PostPosted: Tue Aug 02, 2011 6:26 pm 
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Joined: Sat Sep 20, 2008 8:19 am
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Location: Australia
Here's my solution to sitting in water:

Image

Did a write up on it here: http://yakass.net/articles/equipment-a-preparation/977-pro-ai-seating-mod

And here:


I'm very very happy with it. I haven't thrown out my kayak seat though - held on to that for single hull kayak trips - but wouldn't go back for tri or outrigger style usage.

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PostPosted: Wed Aug 03, 2011 4:55 am 
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Joined: Fri May 27, 2011 7:50 am
Posts: 31
Yakass, Can you provide the specifics of your seat and mounting hardware (although I've found much of your gear list seems unavailable in the US)


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PostPosted: Wed Aug 03, 2011 6:14 pm 
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Location: Australia
Its a folding Skipper seat, and it would be available in the US for sure. Its a generic product. I did try numerous seats though and most were too big. Specs on this one can be found here: http://bla.com.au/index.php?fn=productView&id=733&eId=10&sId=6975fb6b10d3339a2a71e4cb67e82261

Stainless turnbuckles are used to attach and create tension at rear and I am now using cord and jam cleats to secure at the front and sides. Its very secure, very comfortable, much drier, and doubles as a perfect camping seat, ideal for expedition and overnighter use.

I'll update this post with photos of the cord/cleat system I'm now using when I get some photos on the water this weekend.

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PostPosted: Wed Aug 03, 2011 11:27 pm 
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Location: Escondido
NOHUHU wrote:
was under the impression that all scupper holes have a built-in Bernoulli effect of their own, hence one reason they are found on kayaks. While in motion, the Bernoulli vacuum pulls water from the cockpit.
Usually, but not automatically. For instance, the daggerboard well, CB well and drivewell all scoop water in. Scuppers having a teardrop recess behind them generally have a positive Bernoulli effect.
Quote:
So why tape the scuppers? If a larger wing area creates more lift, would not a larger scupper (and more speed) draw water more efficiently?
Tape over the front part of the opening gives a huge boost to the venturi (when going forward). This is nothing new. You may remember the old vent wings on automobiles (that could also reverse and become ram ducts), venturi vents on the roofs of RVs, sunroofs and vent visors on cars. This isn't really about lift.
Image Image Image
Quote:
Or are we talking a "venturi" effect here, where narrowing an opening creates an acceleration of air/fluid which is already under pressure?
No, the boost comes from aligning the exit flow with the slipstream cleanly rather than dumping it. This also reduces drag. Keep in mind, if the boat goes backwards the venturi "vacuum" becomes a ram and the seat area will flood.

To demonstrate this powerful effect, hold a limp piece of letter sized paper with both hands up to your mouth, blow over the top of it (creating a lower pressure slipstream) and watch it lift the paper! 8)


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PostPosted: Thu Aug 04, 2011 5:33 pm 
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Location: Kailua 96734
Man - these guys are FAST!
http://www.kayakfishingmagazine.net/gear-guide/91-new-kayak-gear/1397-ocean-presents-the-venturi-style-scupper-plug.html

Image

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PostPosted: Wed Dec 14, 2011 4:01 pm 
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Joined: Thu Jul 07, 2011 12:57 pm
Posts: 181
Location: Delaware Coast
NOHUHU wrote:


So has anyone tried these yet?


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