# Tunnel Hull- Vented Vs. Non Vented



## Brett

Vented hull is intended to break the vacuum created in the tunnel
by the forward motion of the hull. Venting cuts the drag, increases speed.
Non vented tunnel is usually designed to funnel and squeeze water
into a narrowing tunnel to direct the flow of water to the prop and water intake.
both designs will be slower than a normal hull due to increased wetted surface.

https://picasaweb.google.com/bdefalco/PocketTunnel


Running draft of a standard planing hull can be roughly calculated by measuring
the poling draft of the hull when fully loaded, then adding the distance from
the top of the water inlet to the bottom of the skeg or propeller tips.
Anything less than that distance and the lower unit and prop are chewing bottom.
The tunnel raises the level of the water above the bottom of the transom
when on plane, and so allows the water inlet to be raised up an equal amount.


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## dbraves8

Well I'm just curious if one or the other is going to be a huge benefit or not. I heard tunnels run shallower and that's what I'm looking for. Will I be able to drastically run shallower with a tunnel vs my 16ft action craft with jackplate. Also I've been looking into the sterling tr 7 I was told draft is 5-6 and runs in 2.5-5 inches if water. Is that possible. I'm looking for a boat 16-18ft with a beam top beam in the 80's wider the better. With a decent sized engine so I can run in the mid 30's. It will be used in south west Florida pine island, gasprilla sound areas.


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## Brett

I'm not much for believing advertising claims or sales pitches.
If you find a boat that interests you, go for a test ride.
Do it on a nasty day someplace where there's some extreme shallows
so you can see for yourself how it rides in slop and how shallow it'll run.
Quick way to tell if a boat can really run in 6 inches
is to look at how much paint has been dragged off the lower unit,
how chewed up the underside of the hull is and how dinged up the prop is.

The shallowest I'll run my tunnel is about 12 inches.
Any less and the skeg starts dragging, the prop starts getting dings.
You can see the top of the tunnel and level bubble
and the bottom of the hull and water intake.










If extreme shallow is what you need, then a tunnel jet is your solution.


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## Creek Runner

> Well I'm just curious if one or the other is going to be a huge benefit or not. I heard tunnels run shallower and that's what I'm looking for. Will I be able to drastically run shallower with a tunnel vs my 16ft action craft with jackplate. Also I've been looking into the sterling tr 7 I was told draft is 5-6 and runs in 2.5-5 inches if water. Is that possible. I'm looking for a boat 16-18ft with a beam top beam in the 80's wider the better. With a decent sized engine so I can run in the mid 30's. It will be used in south west Florida pine island, gasprilla sound areas.



Not going to happen my friend, it will run in about 7"-8" at the very least, but it needs every bit of 9" to float at least with a 90hp and top speed is about 32mph. How do I know cause I fish one reguarly with a friend, it's also a very wet boat.

Oh and at that running depth yes we are chewing on the bottom. Better hope there isn't something hard under there.


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## fsae99

Well if you consider dragging the bottom and the prop sub soil but still moving, running. Then it will do it.
Typically running in 2.5" is BS.

Use some common sense here, how well will a prop work if it is more than half out of the water if it is not a true surface piercing prop. Lets say a boat will run completely on top of the water (0" draft) and you had 8" tall tunnel, with a 15" prop typically about 1" above that to cav plate and 1" below that to bottom of skeg so 17" total that leaves the prop about half out of the water. 

Just curious how come you think your AC will run in 10"? Not trying to crack on you or your boat, just have heard same or less running depths only to really investigate and find out that the water was really deeper than the person thought.


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## Creek Runner

> Well if you consider dragging the bottom and the prop sub soil but still moving, running. Then it will do it.
> Typically running in 2.5" is BS.
> 
> Use some common sense here, how well will a prop work if it is more than half out of the water if it is not a true surface piercing prop. Lets say a boat will run completely on top of the water (0" draft) and you had 8" tall tunnel, with a 15" prop typically about 1" above that to cav plate and 1" below that to bottom of skeg so 17" total that leaves the prop about half out of the water.
> 
> Just curious how come you think your AC will run in 10"? Not trying to crack on you or your boat, just have heard same or less running depths only to really investigate and find out that the water was really deeper than the person thought.


Yep!

A Jet Ski won't even run in that, how do I know cause I watched my friend while out ridding our skis try to cut through a little flat that still had water on it, but guess what he only made it about half way and the water was about 4" deep. I have a picture somewhere of it.


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## Sheremeta

Is a pocket tunnel the same thing as a vented tunnel?


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## Brett

This is a pocket tunnel, not very long.










This is a vented pocket tunnel.










The vents (corner rounds) feed air from the transom
to the forward edge of the pocket, breaking the vacuum.










Flow diagram


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## Capnredfish

Brett, I appreciate your workmanship and the info you posted here but, you should be able to run that motor much higher with your tunnel than your pictures suggest. Not an insult , more of a question. I have a non tunnel with the motor way higher than you are running. My last boat was a tunnel but did not run so well, just shallow.


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## Brett

This pic, is of a 5 hp Nissan with a stock 9x8 prop on it.










Had to be that low because the prop didn't have enough cup to deal with the aerated water.

A later setup was with a 9.9 merc with a cupped prop that let me put the anti-ventilation plate
level with the top of the pocket tunnel. And the 9.9 does make her get up and go.


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## Sheremeta

Thanks Brett and cool skiff.


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## dbraves8

> Well I'm just curious if one or the other is going to be a huge benefit or not. I heard tunnels run shallower and that's what I'm looking for. Will I be able to drastically run shallower with a tunnel vs my 16ft action craft with jackplate. Also I've been looking into the sterling tr 7 I was told draft is 5-6 and runs in 2.5-5 inches if water. Is that possible. I'm looking for a boat 16-18ft with a beam top beam in the 80's wider the better. With a decent sized engine so I can run in the mid 30's. It will be used in south west Florida pine island, gasprilla sound areas.
> 
> 
> 
> 
> Not going to happen my friend, it will run in about 7"-8" at the very least, but it needs every bit of 9" to float at least with a 90hp and top speed is about 32mph. How do I know cause I fish one reguarly with a friend, it's also a very wet boat.
> 
> Oh and at that running depth yes we are chewing on the bottom. Better hope there isn't something hard under there.
Click to expand...

ok well what other boats out there in that size range will run as shallow or shallower and float the same or shallower just curious to see what my options are. I want a pratical flats boat but that will run some serious shallow water.


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## dbraves8

> Well if you consider dragging the bottom and the prop sub soil but still moving, running. Then it will do it.
> Typically running in 2.5" is BS.
> 
> Use some common sense here, how well will a prop work if it is more than half out of the water if it is not a true surface piercing prop. Lets say a boat will run completely on top of the water (0" draft) and you had 8" tall tunnel, with a 15" prop typically about 1" above that to cav plate and 1" below that to bottom of skeg so 17" total that leaves the prop about half out of the water.
> 
> Just curious how come you think your AC will run in 10"? Not trying to crack on you or your boat, just have heard same or less running depths only to really investigate and find out that the water was really deeper than the person thought.


I dont know how shallow it really will run i know i have drafted and measured 12" and ran across the same water so 12" i do believe it will run over. I may be wrong however Im still looking for a boat to run as shallow as possible if I do need it.


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## BRunner346

i cant speak for the TR-7 but the hpx-t drafts much more than it runs in. the skiff runs in spit... saying this just based off a couple experiences


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## dbraves8

> i cant speak for the TR-7 but the hpx-t drafts much more than it runs in. the skiff runs in spit... saying this just based off a couple experiences


In your real life experiences what in real world depth do you believe the HPX-T really runs in and drafts real world numbers if you can recall.


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## Swamp

I fish out of a buddies HPX-T a few times a year. I keep telling him if it ever "disappears" to check my place first, fair warning and all that. I was out last Friday with him. We always end up going through water that makes me look for the best ejection path out of the boat because I just know we are going to run hard aground. It never happens and I always look back and see clean water behind us when I expect to see grass and mud. I know we are running 8" probably closer to 6" in small patches. All that can be deceptive though and I usually don't jump out while we are on plane with a ruler. He knows his boat and has never had an issue. It would take a while to get used to doing that if I was behind the wheel. Honestly I would not run a boat over grass intentionally in less that 8", you know it will give the grass a hair cut even if you don't leave scars in the bottom. And yes it will not float as shallow as it runs nor will it get on plane in water it can still run in. I can tell you with certainty it is one very shallow running boat it runs in nothing but that mythical spit.


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## dbraves8

> I fish out of a buddies HPX-T a few times a year.  I keep telling him if it ever "disappears" to check my place first, fair warning and all that.  I was out last Friday with him.  We always end up going through water that makes me look for the best ejection path out of the boat because I just know we are going to run hard aground.  It never happens and I always look back and see clean water behind us when I expect to see grass and mud.  I know we are running 8" probably closer to 6" in small patches.  All that can be deceptive though and I usually don't jump out while we are on plane with a ruler.  He knows his boat and has never had an issue.  It would take a while to get used to doing that if I was behind the wheel.  Honestly I would not run a boat over grass intentionally in less that 8", you know it will give the grass a hair cut even if you don't leave scars in the bottom.  And yes it will not float as shallow as it runs nor will it get on plane in water it can still run in.  I can tell you with certainty it is one very shallow running boat it runs in nothing but that mythical spit.


Thanks for the info I see your also from SW florida. Where at in Sw Florida


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## BRunner346

> i cant speak for the TR-7 but the hpx-t drafts much more than it runs in. the skiff runs in spit... saying this just based off a couple experiences
> 
> 
> 
> In your real life experiences what in real world depth do you believe the HPX-T really runs in and drafts real world numbers if you can recall.
Click to expand...

realistic numbers I would say runs in 6" more or Less... draft is closer to the 8" mark than the advertised 5" or so.


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## Absolut

Brett, Vented tunnels are very popular here in TX, and most people use a anti-cav plate in order to be able to jack their motor higher and run in less water. I don't know if it's true or not, but what I've been told is that it helps direct more water to the prop.


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## Brett

Compression plates are critical on true tunnel skiffs.
Important to keep water around the prop tips to prevent blowout.
Have to hold the "hump' intact until it's past the prop to maintain thrust.


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## jlowens2968

The right tunnel (set up right) will run with the skeg above the bottom of the boat. Even at that, 2.5" (hard bottom) is a stretch. This is how my 17T will run all day and maintain water pressure. Just this last weekend, I ran 1/4 mile across a rock hard bottom flat that was 6" deep. That's about the limit over hard bottom (soft bottom is a whole different story) that I will push it to. The shallower it gets, the more lift you get from compressing the water under the boat and I'm sure my boat would skim along in 2" of water. The only problem is, at that depth you don't have enough water to fill the tunnel, the tunnel loses its suction and you lose grip and water pressure.


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## jlowens2968

One of the best things I've added...


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## Swamp

No problem. I'm in NE Ft Myers just over the Charlotte County line.


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## Sarosi6671

I know this is my first post but I've been a regular lurker for years now. I felt the need to create a profile so that I could chime in on the TR7. I was finally in the position to pull the trigger on a nice boat and I went with a 2008 TR7 with a 90 Yami 2 stroke. For anyone who lives in the Titusville area it was the blue one at BT's marine. 

Since I have never had a nice boat with all the bells and whistles before like this one. I can't stand here and say that it does "this" better than "that" boat. But I can say that it does every thing I've asked it to do and more. 

I bought it from a captain who had 3 of them in the family which one of the boats was actually one of the first few hulls to come out of production. After a while of tweaking the prop set up (5 times) they came up with a custom double cup prop from bauman that really let's this boat do what it was supposed to do from the design concept.

In all I think you would be happy with this boat if you we're to ride in one that had the proper set up. But by all means like every one else has said put eyes on and ride in other boats and the right one will be a clear choice.


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## East_Cape

Cav Plate, Jack-Plate, Heavy Cupped Prop, Water Pressure Gauge, and are all needed for sure and IMHO i'm a fan of the vented prop as it gives more speed and better hole-shot than a non vented tunnel. We've also done some cool stuff with our tunnel design to feed more water and at a higher level than currently offered...
I'll have Video/Pics coming on it as our TX Version were offering has this and I'm building myself a Lostmen and we have a Fury getting it's first tunnel now as well...
If you want a ride I'd be happy to show anybody the plus and minus of a tunnel and what our boats can do as well...
tight lines and good read/thread.
Kevin


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## dbraves8

> The right tunnel (set up right) will run with the skeg above the bottom of the boat. Even at that, 2.5" (hard bottom) is a stretch. This is how my 17T will run all day and maintain water pressure. Just this last weekend, I ran 1/4 mile across a rock hard bottom flat that was 6" deep. That's about the limit over hard bottom (soft bottom is a whole different story) that I will push it to. The shallower it gets, the more lift you get from compressing the water under the boat and I'm sure my boat would skim along in 2" of water. The only problem is, at that depth you don't have enough water to fill the tunnel, the tunnel loses its suction and you lose grip and water pressure.


Well where I run and fish its mainly a soft bottom however If possible to not destroy the skig, lower unit, and motor I would rather not plow through a soft bottom. Any boat can do that but I would rather not tear up the engine or the flats with a prop destroying the bottom. This is the reason Im looking into a tunnel to try to lift as much of the prop/engine out of the water level thats below the boat line to try to not dig the ground so much. I think there are boats out there in the 16-18ft range with a tunnel, jackplate, and cav plate can run in 6-8" which i will be very happy with. I am just looking for someone with real life experience with a boat that will do this type of shallow running.


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## jlowens2968

> Well where I run and fish its mainly a soft bottom however If possible to not destroy the skig, lower unit, and motor I would rather not plow through a soft bottom. Any boat can do that but I would rather not tear up the engine or the flats with a prop destroying the bottom. This is the reason Im looking into a tunnel to try to lift as much of the prop/engine out of the water level thats below the boat line to try to not dig the ground so much. I  think there are boats out there in the 16-18ft range with a tunnel, jackplate, and cav plate can run in 6-8" which i will be very happy with. I am just looking for someone with real life experience with a boat that will do this type of shallow running.


Any of the currently available tunnel boats (TR7, 17HPX-T, Lostmen, etc.) should be able to do that.


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## dbraves8

> Well where I run and fish its mainly a soft bottom however If possible to not destroy the skig, lower unit, and motor I would rather not plow through a soft bottom. Any boat can do that but I would rather not tear up the engine or the flats with a prop destroying the bottom. This is the reason Im looking into a tunnel to try to lift as much of the prop/engine out of the water level thats below the boat line to try to not dig the ground so much. I  think there are boats out there in the 16-18ft range with a tunnel, jackplate, and cav plate can run in 6-8" which i will be very happy with. I am just looking for someone with real life experience with a boat that will do this type of shallow running.
> 
> 
> 
> Any of the currently available tunnel boats (TR7, 17HPX-T, Lostmen, etc.) should be able to do that.
Click to expand...

Is a lostmen or other similar boats where the engine just sits forward into the transom considered a tunnel boat just curious. I have looked at boats where the engine sits up in the rear deck. Will those boats run as shallow as a true tunnel?


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## mkyhagan

I believe what you are talking about are sponsons and those help with balancing out the motor weigh while at rest and might help with hull shot.

On the Maverick hpx-t subject my friend, maverick redfisher on this forum runs an hpx t. You may want to pm him about some of his experiences. I know for a fact i have run in defiantly less than 7 inches on that boat through Bull Bay in Charlotte Harbor on a negative tide. I would say it drafts about 6 inches with 2 people and gear.

hope this helps


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## Absolut

Those are sponsons not a tunnel, and they serve a totally different function.


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## dbraves8

> Those are sponsons not a tunnel, and they serve a totally different function.


Im guessing the sponson makes for a quicker hole shot to get on plane and not make the transom sit so lower in the water to make the boat draft less right?

anything else that it makes a big difference in


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## East_Cape

> Those are sponsons not a tunnel, and they serve a totally different function.
> 
> 
> 
> Im guessing the sponson makes for a quicker hole shot to get on plane and not make the transom sit so lower in the water to make the boat draft less right?
> 
> anything else that it makes a big difference in
Click to expand...



Bingo, better draft and hole-shot. Then add a tunnel and things get good :O)


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## Sheremeta

> One of the best things I've added...


Where did you get that plate?


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## jlowens2968

http://mantaray1.com/


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## disporks

the last two posts got me thinking of a diy project...oh man.

I know it says it on the mantaray site, but would having that plate really allow me to trim my motor higher without cavitation and NOT porpoise without some tabs? My boat doest have some small fixed tabs about 2-3" long by 4-5" wide..


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## jlowens2968

> the last two posts got me thinking of a diy project...oh man.
> 
> I know it says it on the mantaray site, but would having that plate really allow me to trim my motor higher without cavitation and NOT porpoise without some tabs? My boat doest have some small fixed tabs about 2-3" long by 4-5" wide..


Short answer is no, it will make it worse. It actually enhances the bow lift from trimming the motor up. I run with my jackplate fully elevated with trim at about 3 degrees (this is where the cav plate is parallel to the bottom of the boat). It holds good water pressure and I still have good control like this. When the floating grass is bad I'll trim it up to 4.5-5 degrees to help keep it cleared and I need a good bit of tab to hold the bow down.


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