The use of weight on a tunnel.

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Jeffmaturo

Well-Known Member
Joined
Jan 20, 2015
Messages
547
There are a lot of questions new and old tunnel hull racers have. One question that has been present from day one of racing is the idea of placing weight on a tunnel to level it out.

How many of you currently use weight on your tunnel and where do you usually place it.

Is the CG important or completely irrelevant to how it behaves in the water.

I have witnessed the use of an incredible amount of weight to make tunnels handle properly. Would that be considered a design flaw in the hull itself because so much weight was needed or somehow the OB lower mounting and radio gear was off and should be re evaluated?
 
Since I don't run tunnels, I'm going to comment on what I've seen.

At least one ARTR hull was designed with a recess on the bottom of the cockpit for balancing weight so, at least with that boat, weight was figured into the design

As far as CG, it's important in the way any boat runs on the water. Boats that rely on air(tunnels, sport and scale hydroplanes, cats) are probably more reliant on a properly located CG as too far aft will cause the boat to blow over while too far forward will cause it to plow or dive.

Let the flaming begin
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I use lead affixed to the front of the sponsons or front of the radio box to balance my tunnel boats. How much is a matter of testing under a variety of conditions. Once I'm satisfied with the amount of stick on lead, I usually cut out a section of the front tunnel bottom and pour a mixture of equal weight of epoxy and bbs or chopped lead(lead soup) into that area and then resheet the front of the sponson with 1/16" plywood.

JD
 
Exactly Jerry thats how i did my tunnell by cutting a small opening in the tips of the sponsons and epoxy lead soup ..Also because its at the tips less weight is needed as opposed to putting weight in the cockpit or elswhere.
 
I use an adjustable weight mounting system & weight amounts in .5 ounce increments from .5 to 4.0 ounces, as well as a modified PTO mount to make tuning changes possible.

Jim Allen

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I use an adjustable weight mounting system & weight amounts in .5 ounce increments from .5 to 4.0 ounces, as well as a modified PTO mount to make tuning changes possible.

Jim Allen
Jim that looks like a great system!!
 
Jeff.. pm Zaborowski possibly on a pic of his balance board.. its a simple machine that generally most tunnel hulls will balance from 27 to 31% of the hull length... intensively this tool becomes invaluable upon encountering different race conditions... ive been to races from flat good condtions to tape a box wrench on it and hope... now.. I'm not a guy , lazy perhaps.. monkeys with weighting over all.. I have the adjustable system Jim showed in his boat... and while.. ive been down to BBs and epoxy plugs, or split shot in my r box... I leave my boat in a general good on plane state ( weighted, trimmed, angled, whatev..), and ill adjust accordingly at given venues... Midwest water is a fickle encounter... mostly rough... so... test... and test some more... theres not many tunnels take a hurricane... and youll live on that tunnel hull edge... good luck... Mike
 
Jeff.. pm Zaborowski possibly on a pic of his balance board.. its a simple machine that generally most tunnel hulls will balance from 27 to 31% of the hull length... intensively this tool becomes invaluable upon encountering different race conditions... ive been to races from flat good condtions to tape a box wrench on it and hope... now.. I'm not a guy , lazy perhaps.. monkeys with weighting over all.. I have the adjustable system Jim showed in his boat... and while.. ive been down to BBs and epoxy plugs, or split shot in my r box... I leave my boat in a general good on plane state ( weighted, trimmed, angled, whatev..), and ill adjust accordingly at given venues... Midwest water is a fickle encounter... mostly rough... so... test... and test some more... theres not many tunnels take a hurricane... and youll live on that tunnel hull edge... good luck... Mike
I will, thank you.
 
Jeff,

Weight is a key component in the outboard tunnel hull design. Some people design their boats with no regard to anything other than and length, width and maybe looks when in the initial layout stages of a new model and are later faced with adding a huge amount of weight to settle the boat down so that it can be raced without issues. Some boats on the other hand can not carry much weight and if you race this type of boat near the coast where there is a lot of wind most of the time, you have to add weight and if you put too much weight to some models, they begin to have issues because they can not carry much weight.

Years ago a guy purchased one of Tommy Lee's personal XT-460's setup for 7.5cc Modified. This was a boat that NOBODY could beat at the time. After the race was over, Tommy pulled all his gear out of this boat and handed it to Ronnie. I was interested to see how much weight he was running and what astounded me was that he pulled over a pound of lead out of the nose of the boat. I believe it was actually 19 ounces. Now watching this boat run, you would never guess that it was carrying this much nose weight because it was perfectly trimmed and would jump off the corners like a rocket and made lap times like nothing we had ever seen before. This taught me a big lesson about weight, if a boat can carry the weight and is still fast, it is a much more sound setup than a boat that has to be super lite to do the same thing.

Not to say that all heavy boats are the thing to have because that is just not true. Heavy boats do win a lot of races due to the fact they will stay on the water through a hurricane but we are racing here and nobody wants a slow boring pig boat. Its how well the boat responds to weight and its distribution that is the key to having a good race boat. So even though Tommy's boat was carrying a lot of weight, you could not consider it a design flaw because it was by far untouchable at the time.

You do however want the least amount of weight to get the job done.

-Carl
 
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On my Lynx I have a film canister that is mounted into hull at the front of the cowl. I can adjust by just adding lead weight chunks inside. I use a foam piece to keep everything from bouncing around.
 
Jeff,

Weight is a key component in the outboard tunnel hull design. Some people design their boats with no regard to anything other than and length, width and maybe looks when in the initial layout stages of a new model and are later faced with adding a huge amount of weight to settle the boat down so that it can be raced without issues. Some boats on the other hand can not carry much weight and if you race this type of boat near the coast where there is a lot of wind most of the time, you have to add weight and if you put too much weight to some models, they begin to have issues because they can not carry much weight.

Years ago a guy purchased one of Tommy Lee's personal XT-460's setup for 7.5cc Modified. This was a boat that NOBODY could beat at the time. After the race was over, Tommy pulled all his gear out of this boat and handed it to Ronnie. I was interested to see how much weight he was running and what astounded me was that he pulled over a pound of lead out of the nose of the boat. I believe it was actually 19 ounces. Now watching this boat run, you would never guess that it was carrying this much nose weight because it was perfectly trimmed and would jump off the corners like a rocket and made lap times like nothing we had ever seen before. This taught me a big lesson about weight, if a boat can carry the weight and is still fast, it is a much more sound setup than a boat that has to be super lite to do the same thing.

Not to say that all heavy boats are the thing to have because that is just not true. Heavy boats do win a lot of races due to the fact they will stay on the water through a hurricane but we are racing here and nobody wants a slow boring pig boat. Its how well the boat responds to weight and its distribution that is the key to having a good race boat. So even though Tommy's boat was carrying a lot of weight, you could not consider it a design flaw because it was by far untouchable at the time.

You do however want the least amount of weight to get the job done.

-Carl
Good info, thank you.
 
[SIZE=10.5pt]Lots of good people are commenting here, and people that know tunnels extremely well. Here my opinion on weight, and CG. In my opinion focusing on CG can be very dangerous. If you are trying to duplicate CG to someone else, that often can be a very quick way of goofing up your setup. Even if the CG you are duplicating is on the same type of hull. Prop, motor angle, motor height, speed of the boat Act... all work as a relationship to setup and CG. If you set up to someone’s exact CG that works for them, you might find your boat handles poorly. Because you’re not considering the multiple factors that make a tunnel handle. I know on all the tunnels we run, not one of them we know the CG on. In my honest opinion CG isn't really where we focus. Also, as you increase the speed in a tunnel the handling changes quickly. For every 3 to 5 MPH you gain in a tunnel, we've found the set-up needs to change a little with it. If you're running 50, and make a jump to 55 I guarantee you’re going to have to make some adjustments to set up. [/SIZE]

[SIZE=10.5pt] [/SIZE]

[SIZE=10.5pt]As far as weight. When adding obviously the lower you can add the weight the better. Posts above had some great ideas for getting weight as low in the boat as possible. Once we get a boat close we might use a little weight if the boat still has some minor handling issues, but only a little. If you ask my Dad, he believes adding weight should be a 2 to 1 ratio. meaning if you add weight 1 once upfront and 2 ounces in the middle of the boat. If your adding a lot of weight to the front of a tunnel, you'll probably notice you create another big problem. The propeller of a boat is naturally pulling the back end of the boat down. So, if you add a lot of weight to the front of the boat when you back off the throttle for the turn the propeller slows and pulls down the back end less. The extra weight in the front then amplifies the nose of the tunnel coming down hard in the turn. As a result, you see tunnels dart hard in the turn, or roll over. So, adding lots of nose weight most likely is going to make your boat turn poorly. Think of a teetertotter. If a heavier person removes themselves quickly from the teetertotter, the lighter person comes crashing to the ground. Props and lots of nose weight are a very similar relationship. Remove the prop pressure, the nose of the boat comes down hard. [/SIZE]

[SIZE=10.5pt] [/SIZE]

[SIZE=10.5pt]On all the tunnels, we've ever run for records, none of them had over 5 ounces in the front (just in front of the radio box, no weight ever on the nose or tips of sponsons). In recent record runs we've almost removed all the weight. We've focused on the aerodynamics of the boat, rather than weight. I believe you can get much more weight from airflow, than physical lead weight. Likewise, if you don't have to add much weight, entering turns at higher speeds is a lot easier to control.[/SIZE]

[SIZE=10.5pt] [/SIZE]

[SIZE=10.5pt]In my opinion; Propeller, Motor Angle / Height, and Aerodynamics are where I think handling should focus on. Weight and CG are part of the equation, but in my opinion they are much less of what to focus on. The speed of the boat is also a huge factor in the setup relationship. I know I’m repeating but the faster you go, set up will change. Which is why it’s very dangerous to duplicate another boats exact CG. [/SIZE]

[SIZE=10.5pt]Jay Halbrehder[/SIZE]
 
C/G probably is over rated but people that are just getting started need an initial starting point for sure. I have custom models that require no weight at all to trim but you are right, C/G is not something you can't just duplicate and expect everything else to fall into place. After I finish trimming my model and if I like what it is doing, that's when I check the C/G of my boat and record all of the setup parameters to use as a base line so that I can come back to it if I get too far off while trying new things. I am always trying new things. I looked through my computer the other day and counted over 40 tunnels I have played around with over the years. You can spend a lifetime of enjoyment playing around with what can be done with the tunnel boat if you enjoy the design aspect of the sport.
 
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[SIZE=10.5pt]In my opinion; Propeller, Motor Angle / Height, and Aerodynamics are where I think handling should focus on. Weight and CG are part of the equation, but in my opinion they are much less of what to focus on. The speed of the boat is also a huge factor in the setup relationship. I know I’m repeating but the faster you go, set up will change. Which is why it’s very dangerous to duplicate another boats exact CG. [/SIZE]

[SIZE=10.5pt]Jay Halbrehder[/SIZE]

[SIZE=10.5pt]Bingo- Working with Terry and James on the real boat - I learned you need to adjust the boat properly without weight added IF possible . Both my Mod Vp and my B-Stock vision have zero weight added- [/SIZE]

[SIZE=10.5pt]I adjust the rest to make the boat work properly - Prop / Setup are your friends. If your adding weight to overcome an issue- Fix the issue first , and then trim the boat.
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[/SIZE]

Trim is exactly what it is - a FINAL fine tune adjustment- not a fix for an ill handling boat.

Just my worthless .02
 
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Not always ,you can't put negative trim in some boats makes them handle bad in the turns so you have to add weight. Put it this way if your boat is make tons of power you will have to add weight.
 
[SIZE=10.5pt]Lots of good people are commenting here, and people that know tunnels extremely well. Here my opinion on weight, and CG. In my opinion focusing on CG can be very dangerous. If you are trying to duplicate CG to someone else, that often can be a very quick way of goofing up your setup. Even if the CG you are duplicating is on the same type of hull. Prop, motor angle, motor height, speed of the boat Act... all work as a relationship to setup and CG. If you set up to someone’s exact CG that works for them, you might find your boat handles poorly. Because you’re not considering the multiple factors that make a tunnel handle. I know on all the tunnels we run, not one of them we know the CG on. In my honest opinion CG isn't really where we focus. Also, as you increase the speed in a tunnel the handling changes quickly. For every 3 to 5 MPH you gain in a tunnel, we've found the set-up needs to change a little with it. If you're running 50, and make a jump to 55 I guarantee you’re going to have to make some adjustments to set up. [/SIZE]

[SIZE=10.5pt] [/SIZE]

[SIZE=10.5pt]As far as weight. When adding obviously the lower you can add the weight the better. Posts above had some great ideas for getting weight as low in the boat as possible. Once we get a boat close we might use a little weight if the boat still has some minor handling issues, but only a little. If you ask my Dad, he believes adding weight should be a 2 to 1 ratio. meaning if you add weight 1 once upfront and 2 ounces in the middle of the boat. If your adding a lot of weight to the front of a tunnel, you'll probably notice you create another big problem. The propeller of a boat is naturally pulling the back end of the boat down. So, if you add a lot of weight to the front of the boat when you back off the throttle for the turn the propeller slows and pulls down the back end less. The extra weight in the front then amplifies the nose of the tunnel coming down hard in the turn. As a result, you see tunnels dart hard in the turn, or roll over. So, adding lots of nose weight most likely is going to make your boat turn poorly. Think of a teetertotter. If a heavier person removes themselves quickly from the teetertotter, the lighter person comes crashing to the ground. Props and lots of nose weight are a very similar relationship. Remove the prop pressure, the nose of the boat comes down hard. [/SIZE]

[SIZE=10.5pt] [/SIZE]

[SIZE=10.5pt]On all the tunnels, we've ever run for records, none of them had over 5 ounces in the front (just in front of the radio box, no weight ever on the nose or tips of sponsons). In recent record runs we've almost removed all the weight. We've focused on the aerodynamics of the boat, rather than weight. I believe you can get much more weight from airflow, than physical lead weight. Likewise, if you don't have to add much weight, entering turns at higher speeds is a lot easier to control.[/SIZE]

[SIZE=10.5pt] [/SIZE]

[SIZE=10.5pt]In my opinion; Propeller, Motor Angle / Height, and Aerodynamics are where I think handling should focus on. Weight and CG are part of the equation, but in my opinion they are much less of what to focus on. The speed of the boat is also a huge factor in the setup relationship. I know I’m repeating but the faster you go, set up will change. Which is why it’s very dangerous to duplicate another boats exact CG. [/SIZE]

[SIZE=10.5pt]Jay Halbrehder[/SIZE]
Jay I thought this was an excellent and informative post. I have just one question, why the 2 to 1 ratio? Does adding weight to the middle of the boat help it transition in the turns when there has been weight added up front?
 
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