tunnel bottom side ?

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Bruce Clark

Well-Known Member
Joined
Oct 27, 2013
Messages
111
Seems like there are lot of good tunnels on the market.  What I would like to talk about is the bottom.  What makes one turn better or what it takes to keep one on the water at higher speeds. I know there are a lot of different thoughts about width, height, or design of the sponson.  I would really like to hear from the designer of the people that make boats.  I am hoping that information shared will help people go faster and be more competitive.  I really like the IW website, good job guys.
 
To me the biggest advance in smaller tunnels was the increase in sponson dead rise angle.  The deep vee effect gives better handling in rough water but the issue then becomes cornering.  The universal solution has been stumble blocks to keep the bow up in the turn.  For comparison the Shaman has 17 degree dead rise on the left sponson and 20 degrees on the right.  Most other tunnels use 15 degrees on both sponsons.  Different sponson heights on the right and left sponson also help in the turns.  The biggest factor in high speed running is the tunnel width, length, angle and position relative to the sponson trailing edge and angle of attack.  Very fine adjustments between the sponson and tunnel wing angle of attack determine the flight characteristics at speed.

Lohring Miller
 
I've been toying around with autodesk autocad trying to design my own tunnel hull. Does more dead rise angle increase stability in rough water or is it mostly for turning?
 
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I have looked at the HTB 3.5  the Vision 3.5  Links 3.5  and the VS 1 but I have not studied all of the angles.  Seems like the tunnel has a vacuum so I can understand letting more air out the back to increase speed.  Is this where the width of the inside tunnel makes a difference.  Less air less vacuum or wider tunnel to let more air out.   To me the deeper sponson would be better for rough water.  Personally I like for my tunnels to run flatter on the water but get more speed when I run nose high and let off throttle to make it turn.  Has anyone drew one up with the wind tunnel to see any changes that would improve the boat.  Guess I'll be playing more with the bottom. 
 
Tunnel hulls have to ride on slight pillow of air pressure in order to "fly" correctly. Getting the correct amount of pressure is crucial. This, combined with carrying the correct geometry needed to get the model around the turns without getting too wet or acting like a total fool is where the entertainment comes into play. Figuring this out can take a while (even years) because you will find most often that fixing one thing screws up something else and soon you will be chasing your own tail.  It is very challenging and time consuming to tune bad traits out of a tunnel boat.  Tunnel boats are NOT easy to get right because they are typically ill handling little creatures.  My advice is to take your time and watch boats that look like they are easy to drive and start developing YOUR OWN ideas of what you think is actually happening and then build a prototype to prove or disprove your ideas. Stick with it and don't be afraid to change something no matter who tells you it won't work. Just cut you own path. Get determined to figure it out and you should produce a competitive model. 

-Carl 
 
If we are talking rough water stability in the straights, I found 17deg deadrise good (same for port and starboard), 24mm deep tunnel at transom, but also important is the height of tips and the way the sponsons rise to the tips from the 'flat' (side view) of the ride pads.

Now, the fun is to make to go fast in the straights AND the corners :)   That is where a lot of designs differ. (ie some do a lot better than others)

Kris

View attachment 736mm Dragon Racing Tunnel-Model.pdf

View attachment 736mm Dragon Racing Tunnel.dxf
 
Bruce Clark said:
I have looked at the HTB 3.5  the Vision 3.5  Links 3.5  and the VS 1 but I have not studied all of the angles.  Seems like the tunnel has a vacuum so I can understand letting more air out the back to increase speed.  Is this where the width of the inside tunnel makes a difference.  Less air less vacuum or wider tunnel to let more air out.   To me the deeper sponson would be better for rough water.  Personally I like for my tunnels to run flatter on the water but get more speed when I run nose high and let off throttle to make it turn.  Has anyone drew one up with the wind tunnel to see any changes that would improve the boat.  Guess I'll be playing more with the bottom. 
Click to expand...
Bruce,

Pick out two similar designs to study that both run good and don't even consider thinking about or wasting time looking at models that perform poorly.  Then build your prototype boat.  

When you finish it, keep good records of what you change and what your change did to your trim requirements. Keeping good notes is very important.
 
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I'll warn you, actively designing boats is addictive. A fairly good performing boat can be built with common sense. Once you start testing and making changes you will find that it becomes a 'chase' of continuous improvement. In other words, you can build a better mouse trap but you will never build the perfect mouse trap. It is a fun challenge. When making changes, make one change at a time. Like Carl said, take notes. I did that from the time I built my first boat and it helps to have that information written down.  Another thing that can help is having good pics taken of the boat on the water. I learned some key things about my boat after buying good quality pics from some of the event photographers that come to the races. 
 
Lots of great info and discussion, thanks guys.  B)
 
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Carl Van Houten said:
Tunnel hulls have to ride on slight pillow of air pressure in order to "fly" correctly. Getting the correct amount of pressure is crucial. This, combined with carrying the correct geometry needed to get the model around the turns without getting too wet or acting like a total fool is where the entertainment comes into play. Figuring this out can take a while (even years) because you will find most often that fixing one thing screws up something else and soon you will be chasing your own tail.  It is very challenging and time consuming to tune bad traits out of a tunnel boat.  Tunnel boats are NOT easy to get right because they are typically ill handling little creatures.  My advice is to take your time and watch boats that look like they are easy to drive and start developing YOUR OWN ideas of what you think is actually happening and then build a prototype to prove or disprove your ideas. Stick with it and don't be afraid to change something no matter who tells you it won't work. Just cut you own path. Get determined to figure it out and you should produce a competitive model. 

-Carl 
Click to expand...
This can be applied to all boating. Most want to be told how to do it. Those that actually change things and find out for themselves what that does will learn more. Do this enough times and you will be able to predict to a certain degree what works. Then you jsut have to build it and test. This is one of the aspect of the hobby that I enjoy. 

Nice post Carl

Mike
 
This is one of the reason I didn't race this year.  Been doing a lot of testing with 3 boats and they all have different bottoms.  I haven't run the latest but its more like the VS1.  I think it will be fast but I want to go through the corner at a faster speed like I have seen some JAE riggers.  I wasn't racing in 2011 but the post above supplied a lot of information about this post.  Rodney Pierce had the post with the picture in it.  Great reading material.  Thanks Chris Dixon.   I do have another ideal to build and test that I have never seen on any tunnel boats.  If it works I will share what I learn from it. 
 
No problem Bruce Clark. I am a newbie on boat design....I found that post by Rodney pierce a while back and it answer a lot of my questions. I've yet to build a tunnel but I have a tunnel kit on the way that was designed by someone else. I hope it gives me some ideas while I build it.
 
Great post Carl and Lohring

Like Lohring said about aerodynamics and hydrodynamics has to work together to have a good running boat.

Dave
 

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