Vented tunnel????

**rutro** · 03-13-2010, 01:15 PM

I learned a new word, vented, and in conjunction with a tunnel hull it makes a difference in top speed and rpms. Has anyone here had any experiance with these? Seems as though they have been arround for ever but not everyone know how or why... some boats come with and some can be added on and I need to do it myself,

, as allways!!!

**Mark75H** · 03-14-2010, 05:51 PM

Never heard of it. Can you give a link to where it is discussed?

**M. HARDEE** · 03-14-2010, 06:17 PM

Would be referring to a tunnel with vent chanels in sponsons mostly used on large offshore cats and v bottoms

**afr** · 03-14-2010, 06:36 PM

sam thats what i did to my bottom just we call it atomized the big hydros use a slat system to atomize there running surfaces
if i undestand it right myself

**rutro** · 03-14-2010, 06:40 PM

Hey thanks for the replys. It is apparently used quite a lot on the tunnel hull flats boats. They seem to get a hydraulic lock with the water in the tunnel and thats great when you're running skinny water. But when I get out in the bay and want to go it won't, so to speak. So someone figured out that running a pipe or tube to the front part of the tunnel with a valve on top would, when the valve is open, let the air break the lock and the water in the tunnel lets go. The motor must be let down to keep water to the lower, but most usualy a 1000rpm gain and better fuel economy is a result. Now I'm beganing to understand how some of these cats are going so fast. There are some outrageous fast flats boats down here......... some of them are sponson type cat hulls and I understand those. But then there are these other tunnel hull boats that smoke they go so fast.

**John.Vaught** · 07-28-2010, 06:17 PM

Rutro,<O

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I have a 23V Tunnel Kenner that has a pocket tunnel on it as you know the hull actually lifts water up higher as it passes over it. Resulting in a negative pressure area in the pocket tunnel, I believe that having a controlled vent would give you the ability to run with the tunnel primed or vent it to give less wetted area and more efficiency and a higher top speed.
From what I have read as much as 15% can be realized.

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I am very serious about making the modification but want some insight from the experts; most people on this forum are more familiar with hull modifications than some of the other forums.

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I have been fishing for someone to help me because I don’t want to drill a lot of holes trying to find the sweet spot, also I need to know how big the vent needs to be, CFM of the tubing ect.
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I know a lot of flats boats are venting pocket tunnels now as you can see in this video
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http://www.vimeo.com/2821624
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Thanks

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Big John<O

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**rutro** · 07-29-2010, 11:17 AM

Hey Big John, I was looking into this very serriously and had trouble finding anyone who even knew what I was talking about. As far as I know there is no formula and a lot of guys just experiment until they get it right for the rig they have. I did find out that a lot of the aluminum boats like the duck hunters use come rigged that way. The one thing that's necessary for sure is a baffle over the opening in the tunnel, this is so the water wont tend to squirt up out of the tubing when you come down off plane. The concensus is that the sweet spot is right at the beganing of the tunnel and the size just cant be to big but can be to small. I've been so involved with helping my Dad this summer I have not even had the boat out. His health is bad and at 82 that is just one of the probs that catch up with ya. I just wish I had known about this when I had the console off this Kenner, it would have been easy to cut some stuff in then. It was sudjested that I run pvc pipe from the transom up the tunnel to the front of it and put a ball valve at the back to see if it would be worth doing it permanent later on. And I may do that later on this summer, just don't know right now what I'll be able to get done.

**WATERWINGS** · 07-29-2010, 11:36 AM

subscribed

**John.Vaught** · 08-16-2010, 05:25 PM

Well,<O

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I have been looking into venting my tunnel; there are some raw water through hull fittings that I think will work if I turn them around backwards. <O

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Does anyone have any pictures of the way the aluminum guy’s tunnels are vented?

I know venting it will help the boat, when we get in some rough water the boat gets up on plane higher and runs faster. It also handles better.<O

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There is an insane amount of water that comes out of the tunnel at 46 to 47mph; I know that must be slowing us down it looks like a flat version of a jet boat rooster tail.

If anyone has any insight please let me know.

thanks,

John

ps I hope your dad gets to feeling better<O

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**vnemous** · 08-16-2010, 06:59 PM

I was reading something on the Hydrostream website about them venting the Vulture hull with plastic tubes to let the air out.

**afr** · 08-16-2010, 07:21 PM

here we go these guys cover just about every design

http://www.boatdesign.net/forums/boa...elp-18879.html

hope this helps

**zduckdogs** · 08-16-2010, 07:25 PM

this is what i read on another duck hunting site i am a memeber of...they vent their tunnels often.

the first is a picture from underneath looking into the tunnel

this picture is a view of the vent pipe welded into the seat of the aluminum boat.

i imagine for fiberglass you could fashion something similar.

but youd think that the factories making the tunnel boats would have discovered this by now

The tunnel area of these boats is a very low pressure area. Because of the low pressure, the rear of the boat sucks down to the water. The vent helps break that suction allowing the rear of the boat to break free of the water. It also assists in takeoff by ventilating the propeller allowing a small amount of slippage letting the outboard build rpms which are required to build horsepower. I know from experience it works quite well

hope this helps

bob

**John.Vaught** · 08-16-2010, 09:37 PM

Could I install something like this at the beginning of the tunnel? And get the same result?

http://www.go2marine.com/product.do?...F&WT.mc_id=gb1

http://www.freshwatersystems.com/p-2...m_term=0723409

**John.Vaught** · 08-16-2010, 10:18 PM

Would one big vent be better or several small ones?

**zduckdogs** · 08-17-2010, 07:05 AM

I am under the impression that it is JUST to break the vacumn....so anything very big will start to have other effects, you might not want..

you can break vacumn with a 3/8"th tube!!!

dont know the ramifications of a larger tube really...

bob

bob

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