# tunnel hulls explination



## ryderfzr (Jul 6, 2015)

hey everyone my friend and I just picked up a 16' tunnel hull for a really great price. it looks like a bossman or a morgan marine. my question is what is the purpose for the tubes that are connected at the start of the tunnel? we are thinking of redoing the entire skiff and I like to understand things before I tear into them thanks guys ahead for your help. I will post pics in a bit


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## Smackdaddy53 (Dec 31, 2012)

Post photos if you can. It sounds like a vented tunnel but more explanation or photos would help.
A vented tunnel will in theory perform better than a regular tunnel because it is supposed to break the suction caused my the upward movement if water while the boat is under power causing better holeshot, cleaner water to the intakes and prop and higher speed due to reduced drag. Are there valves on the tubes anywhere and where do they end up?


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## GullsGoneWild (Dec 16, 2014)

sounds like a vented tunnel


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## ryderfzr (Jul 6, 2015)




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## ryderfzr (Jul 6, 2015)

the vent I think comes up in the center console with no valve that I see. If we redo this boat I just want to do it right


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## commtrd (Aug 1, 2015)

Never seen a tunnel done like that...


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## Smackdaddy53 (Dec 31, 2012)

I’ve never seen a vented tunnel setup like that but it appears to be a vented tunnel for sure. Most just have a fkat plate at the front of the tunnel with one hose fitting under it with the hose running out of the transom or with a valve and stand pipe.


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## ryderfzr (Jul 6, 2015)

Smackdaddy53 said:


> I’ve never seen a vented tunnel setup like that but it appears to be a vented tunnel for sure. Most just have a fkat plate at the front of the tunnel with one hose fitting under it with the hose running out of the transom or with a valve and stand pipe.


why would it have a valve if it is to intake air? or you mean like a backflow preventer


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## GullsGoneWild (Dec 16, 2014)

I don't think its necessarily an air intake. I think the purpose of vented tunnels is to add speed by decreasing the airflow in the tunnel. I could be way off base here but I remember seeing an Eastcape vented tunnel video that shows the driver closing the vent and rocketing forward like he hit a new gear. Like I said I could be wrong and its just a guess on my end.


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## Smackdaddy53 (Dec 31, 2012)

GullsGoneWild said:


> I don't think its necessarily an air intake. I think the purpose of vented tunnels is to add speed by decreasing the airflow in the tunnel. I could be way off base here but I remember seeing an Eastcape vented tunnel video that shows the driver closing the vent and rocketing forward like he hit a new gear. Like I said I could be wrong and its just a guess on my end.


The vent is to let the air out of the tunnel, not in. Basically a carb to release suction some tunnel hulls have while jumping on plane. Think of a suction cup with a hole in it and one without a hole in it. Which one sticks better? I’m sure the guys at EC can explain the whole system more intelligently but I think the valve is just used to shut after you get on plane and some leave it cracked while running. They are all different just like everything else on our different rigs. Some tunnels don’t work with a vent, some do.


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## Capnredfish (Feb 1, 2012)

That's an old tunnel design Majestic/Savage creek used. That design just sucked the boat down so the vents helped break the suction. Ask me I know. Had a Savage leak. Mine had one vent. Blocked it while experimenting with my own ideas on that tunnel. As soon as it was starting to move the stern went under water. I quickly got off gas and removed my block. Others have done vented and adjustable venting including the original Beavertail company. 
Those look like a lot of bandaids on the tunnel design.


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## commtrd (Aug 1, 2015)

Capnredfish said:


> That's an old tunnel design Majestic/Savage creek used. That design just sucked the boat down so the vents helped break the suction. Ask me I know. Had a Savage leak. Mine had one vent. Blocked it while experimenting with my own ideas on that tunnel. As soon as it was starting to move the stern went under water. I quickly got off gas and removed my block. Others have done vented and adjustable venting including the original Beavertail company.
> Those look like a lot of bandaids on the tunnel design.


Very interesting discussion.


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## ryderfzr (Jul 6, 2015)

Capnredfish said:


> That's an old tunnel design Majestic/Savage creek used. That design just sucked the boat down so the vents helped break the suction. Ask me I know. Had a Savage leak. Mine had one vent. Blocked it while experimenting with my own ideas on that tunnel. As soon as it was starting to move the stern went under water. I quickly got off gas and removed my block. Others have done vented and adjustable venting including the original Beavertail company.
> Those look like a lot of bandaids on the tunnel design.


We are currently pulling the cap to reinforce the super thin hull I did read about that but figured that would be an easy thing to do. Just wasn't sure what these air valves were for. The hull seams to be identical to a bossman or a Morgan marine except for the vent hole setup and if we are redoing the hull maybe change the setup


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## Mike C (Feb 27, 2017)

Just to throw anther thought into the mix.
The "venting" could also be a venturi system instead of a vent.

The aft side of this "vent" causes a drop in pressure due to the water flowing over it. The drop will cause air to be sucked into the tube from its inlet at a higher rate than the water flow on the aft end of it.
One of two things should happen as air is drawn in and forced out.
The first is that the air will cause separation of the water from the tunnel hull and increase lift.
The second is the velocity of the air should cause a pushing effect and increase the speed of the boat.
I could be wrong though.
Here's an example of a venturi vacuum.
Hook up an air hose, pull the trigger and air pressure is sent towards the bag through the tube. This causes tremendous suction on the open end of the tube.
Same scenario as the hull mentioned above except air causes the suction.
Something to think on


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## Anderson Guide Service (Feb 17, 2017)

Looks like a vent. None of the Texas boats are vented anymore. I think it was more of a theory (or gimmick) and a design hoping to gain a little in the hole shot but there is really no benefit. I suppose there might be with a very small outboard that doesn't have as much power to break suction but I would doubt it. Even a small motor moves a lot of water water movement is what you need.


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## Smackdaddy53 (Dec 31, 2012)

Anderson Guide Service said:


> Looks like a vent. None of the Texas boats are vented anymore. I think it was more of a theory (or gimmick) and a design hoping to gain a little in the hole shot but there is really no benefit. I suppose there might be with a very small outboard that doesn't have as much power to break suction but I would doubt it. Even a small motor moves a lot of water water movement is what you need.


I beg to differ as always...I’m about to vent mine. It’s not a gimmick at all, it’s physics. It has less to do with hole shot and more for top end gains. Why do you think non tunnel hulls run faster with less horsepower than the exact same hull with a tunnel and more horsepower? The tunnel sucks the stern down as water moves upward causing a loss in speed and efficiency. The vent cancels some of this suction out by equalizing the pressure.


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## Reel_Lucky2 (Sep 19, 2012)

We have a vented tunnel on a Beavertail BTX and it makes a huge difference. The benefit is when running, not hole shot. When you open the vent the stern rides a few inches higher and you can feel the hull release. It really takes off. You will lose water pressure when jacked up though when vented. You have to lower the jackplate or it will overheat. You have to come off plane and stop to get the tunnel to fill back up with water.


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## DuckNut (Apr 3, 2009)

Definitely vents. However, those two after thoughts glued on at the back are driving the bow down much like a hook in the hull.

Looks more like an experiment than finished product.


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## Capnredfish (Feb 1, 2012)

Savage leak boats was an experiment for sure. How not to build a boat..


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## ryderfzr (Jul 6, 2015)

The two in the back ended up not being vents but the drains from the well in front of the motor. The only real vent I have located was at the front it was not done like the others I have seen recently with the plate


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