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Old 10-20-2006, 10:29 AM   #1
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Arrow Controversy over the frame rust. by "Boatdoc"

Top of the morning everyone;
The post titled as "Mystery of the frame rust revealed" through the responses exposed the existence of misconceptions as to when, and why it happens. This title was used to find out what lay on the other side of proverbial fence. By wearing few different high titled hats during may forty years in the industry, I have learned that a proper approach to the problem is relative to the outcome. When faced with a problem, we first need to determine what, and why it happened. Replacement of components with new, only buys you extra time and does not necessarily resolve a problem.
All failures involve a reason. If we exclude from this statement pre engineered obsolescence and poor workmanship, we can maintain our sanity and continue to look elsewhere for answers. When things fail, and you are determined to correct it, you better come up with positive identification of the reason for failure.
Unless the product is under warranty, complaints will not provide a resolve.
Even during the warranty term, replacement may only buy the manufacturer the time till it's expiration. Component failure due to wrong installation or application are very common today in this competitive market. But when we have to pay for it, it is our choice to upgrade. Wrong application by the same token, does not mean that the product failed because of quality issues. Builder may have simply chosen a part not suitable for particular application or perform that task.

In our quest for fast buck, we often forget about Mother Nature. At times we like to believe that it is very easy co combat her effects on our product, which in reality she can turn it into obsolescence. The truth is that in some cases, this fight can be futile with our choice of materials or technology. While some of the afflictions are impossible to combat, in many cases we can at least reduce the adverse effects by understanding and respecting the laws of nature.
That being, if we cannot alter the environment, we may have to alter the design, material or application and at times it may include the function.

Forgetting the poor quality in AS frame coating, when we own one, we have a problem with rust which needs to be addressed. The task of totally eliminating frame corrosion can be extremely expensive. Even the galvanized frames when enclosed especially in salt air environment will oxidize and harm the aluminum. In such cases we need to consider the next best and most reasonable approach. That next approach may not be a cure. Our remedies may be countered by many natural phenomena's which are hard to eliminate.
Therefore we must work with them, instead of fighting things we cannot change. Yes, that is a part of Serenity Prayer.

Many of you have the notion, that you can easily and successfully combat the elements of nature and her phenomena's with cheap and easy fixes.
I will bet on Mother Nature winning over you every time. If anyone thinks that she or he can inexpensively eliminate the condensation in the belly pan, I sure would like to hear from that person. Phenomena of condensation is a part of nature's works which cannot be eliminated by a cheap fix. So, if we cannot eliminate it lets vent it, drain and dry it ASAP. All of the sealing of the pan will not stop condensation, it will just hold more water so will your fiberglass insulation unless you vent it.

Let us shake off the myths and mysteries, and realistically approach the problem at hand. While the frame design itself is a part of the problem, complaints are of no value to anyone. At least in the older AS's the cross members were formed with a upward bend on the bottom, forming an excellent pooling condition. Closed outriggers divide the banana wrap into many chambers for condensation to take place. Guess what happens if you seal the banana wrap on the bottom side? Guess what happens when the belly skin overlaps the banana skin? Water inherently clings to surfaces, filling most minute gaps which are the most difficult to dry up. Why do you suppose frames rust on horizontal surfaces first? I do not expect any of you to respect my knowledge, but shame on you if you disrespect Mother Nature, her laws and phenomena's.

Let's examine the phenomena of condensation first. When you contain a mass of air and heat it, and than place it in opposing temperature environment the temps will eventually equalize. But, until that happens condensation will take place. Pending the difference in temps, time of that cycle is relative. It is so, because the two opposing temps can only meet at the surface which separates them. This barrier than acts as accumulator.
Condensation in such case is unavoidable, unless you separate the opposing temps with 100% effective temp barrier. There is no cheap way to do it in the belly pan short of foaming it in with urethane closed cell foam. Your floor will stay dry and be well insulated, but how will you get to perform repairs if needed? Urethane foam is very expensive, and yes, you would eliminate the condensation.

Let us for a moment presume that we are camping in a desert, where the heat of the day reaches 120 degree. In the evening the temps drop suddenly and drastically. Warm air rises, correct? The belly pan and banana wraps keep that hot air from escaping, while much lower temps collide at the skins which divides them. Until that process of temp's equalization is completed condensation takes place. Again the rate is relative to humidity factor, spread in temps as well as volume of air and time frame involved. Have you ever wondered why your car A/C drips water when used?

While we cannot easily prevent that process, we can minimize the adverse effects of it. It can be done by drawing the air through the belly pan so that equal temps can be maintained inside with temps outside. This is not a rocket science, those are laws of nature. For as long as we prolong the venting, draining and drying process, frames will rust much faster.

Another phenomena of water entry, occurs while towing in the rain, and that aspect it is most overlooked. At stand still, water is pulled down by law of gravity. It also inherently cling to surfaces, but never travels up unless is forced by stronger than gravity force. This is where drastic differences take place, so let's examine that phenomena. Just assume we are traveling at 60mph against 30mph headwind. Now your AS is exposed to 90mph wind factor. It is plenty of force, to drive water horizontally on the surfaces. The water is forced to be displaced along the surfaces of your AS. Because your belly pan is sealed from that external pressure it will maintain close to atmospheric pressure while outside pressure is much greater. With this imbalance in pressures the belly pan becomes a "low pressure area", comparing to outside pressure. Forced by external pressure water, will seek easiest path which is your belly pan acting as the low pressure chamber. If given the entry point the water will be drawn in, rather than being displaced along the skin.
This is why it is important, that your belly pan skins are arraigned in a shingle effect front to back. This will prevent the water from being driven in by external pressure. Banana wrap should overlap the belly pan skin. Each compartment in the belly pan should have a drain. Each section between outrigger should have small slit drain. But all these drains will have a funneling effect into the belly pan while towing, right? Yes you're right.

Two things will have to be provided to minimize the effect. One is to provide a intake for air so that the pressures are permitted to equalize. This is where it gets tricky. First this intake must have a water deflector. No problem, but let's just leave that for a moment. To speed up the drying process inside your belly pan, installation of a small computer type fan operating on 12 or 24 Volt DC should be installed into belly skin in the rear. They draw mere 0.17 Amp which is no threat to battery, but they will pull a lot of air through the belly pan, providing your insulation is not hanging down and restricting the flow. Both entry point should be protected with Stainless Steel screen. [plastic screens may tear too easily] This fan should be turned on when you reach your destination to help dry. Let's get back to the intake now.
If the air intake must be open to pressurize the belly pan, than the fan exit must be closed to stop the vacuuming effect at the fan. A hinged, secure able cover must be installed over the fan exit during towing. This will prevent the air from exiting the belly pan. Caution must be used here, not to provide a too large of a air entry which may cause extreme pressures in the belly pan and damage the skins.

Outrigger do not hold a large mass of air, therefore condensation will not produce a lot of water and small slits in each section will drain it. From here you can only hope for the best in outrigger area. For the belly pan, drain bladders are the best choice. Tempo marine Products has a product called ADP[automatic drain plug]. While the entire kit is not applicable to us the bladder is. I have seen similar smaller bladders used in doors in auto industry. The bladder part of ADP is about 1" in ID. It can be attached with 3M 42 or 5200 sealer, but allow sufficient time to cure before traveling.
Attaching it over 3/4" hole from underside would not leave a flange on inside thus allowing for good drainage. Leave the rest to your fan when you reach your destination point.

While all of those recommendations are not leading to a total cure, they are at best simple and inexpensive remedies which can be implemented to prolong frame life. No one is expected to honor or follow my recommendation in this post. If you have a better idea, let us hear it. For those who wish to argue over the laws of Nature and her physics, let me just shut up and go away.
My time is very valuable in my business and those recommendations are not posted for my benefit. Thank you for your ear, " Boatdoc"
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Old 10-20-2006, 11:02 AM   #2
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I agree except the fan install.

I don't think it will work that well, you will be bringing in moist air on certain days as well as dry on others. So how are you going to control that? We can't focus on this to that degree it's just too much this is a vehicle to have fun.

I think the drain holes are a great idea but the bladder things in the bannana skins are not needed they can get similar drain slots or holes.

Also at least on mine I have 6 belly compartments 3 in front of the axles the center and bannana on each side and again 3 in the rear. So now were talking about two fans....just too much...While you may do it because you're really into this, the average owner will not.

There is another way to look at this issue say you clean up everything below POR the steel, fix the insulation put in drains etc.

Just check it in 5 or 10 years, the belly pans can be dropped inspected and repainted as needed. Drill out 50 rivets or have inspection holes this would become standard maintenance, like checking the brakes.

Remember for these units to have reached the stage of disrepair we're talking about took in most cases 25+ years.

But my belief is that the number cause is the fiberglass insulation, this must be discarded in the belly and foil bubble or something put in it's place.

We're not building musem pieces here, I'm trying to restore this rig to use it for the next couple of years without worrying about these issues.
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Old 10-20-2006, 12:30 PM   #3
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Hi Bob; You have missed the whole point. If the temperature inside your belly pan is close to the temp outside the condensation does not take place. Damp day is a damp day and there is nothing you can do to change it.
You cannot seal the belly pan from humidity. We are talking about minimizing condensation by ventilating and drying it by drawing air through wet belly pan due to condensation. I like to know how do you paint the frame with the floor on it. Or do you think that moisture will not reach it? Thanks for your imput Bob. I will shut up and go away now "Boatdoc"
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Old 10-20-2006, 12:52 PM   #4
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Quote:
Originally Posted by boatdoc
I will shut up and go away now "Boatdoc"
Keep talking you have a lot of valuable input, I enjoy it as I'm sure others do as well.

So don't go away, stay and keep on "Streamin"
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Old 10-20-2006, 03:08 PM   #5
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Boatdoc,
You have obviously given this some thought, and I think your points are valid. Whether anyone wants to take any corrective measures will of course be an individual choice. Keep posting!
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Old 10-20-2006, 03:14 PM   #6
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The automatic drain plug to which boatdoc is referring is shown on the site:
http://www.tempoproducts.com/2004/drain_plugs.html

I thank boatdoc for his in-depth consideration of the problem of moisture entrapment in the enclosed belly of our Airstreams.

However, it is not clear to me that the enclosed belly volume will be a "low pressure" area during travel. Surfaces exposed to airflow approximately parallel to the surface will experience the venturi effect, wherein the pressure at the airfoil surface drops as the air velocity increases. (See a simple explanation at http://www.answers.com/topic/venturi-effect).

The practical result of this is that the air flowing along the belly surface will likely be at lower pressure than the volume in the belly, and would induce moisture and gas out of the enclosed bellypan.

Without a bit more analysis or experimentation I'm not clear that this effect is pronounced enough along the belly surface to cause a pressure differential which would activate the operation of such a drain plug.

Boatdoc's points about the inevitability of moisture entrapment in the belly are valid. We can debate possible methods of removing the moisture, and there are ways to provide some protection to metal surfaces for that moisture, liquid or gaseous, which will be present.

Thanks to all for the continuing discussion.
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Old 10-21-2006, 04:43 AM   #7
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Hi Marshall; It looks as my layman terms did not explained it properly.
#1 ADP drain has nothing to do with pressures. It is a drain, and gravity on water causes it to open, thus draining water. Bladder closes by design, no water present it stays closed and stops bugs.
#2 Fan does not get rid of condensation. It helps to equalize temps by drawing air through. No temp differences, no condensation. Nothing you can do about humidity, short of a air conditioner. While humidity is a factor which increases volume, it is the temp differential that causes condensation.
#3 While your reference to venturi effect is correct, AS surface is not exposed to to ideal lab conditions. While parts of AS act as airfoil, the pressure drops behind it . AS belly being low, encounters Ground Effects changing the pressures. Tow vehicle also creates low pressure slowing the air speed behind it. Air flow around your AS is subject to continuous changes in air flow. Did a tractor trailer pass you? First you are pushed away, then it pulls you in. Pending the direction of the wind, air flow around your AS will constantly change. If the pan was 100% sealed to air [which is not] it would not be affected by external forces. Increased air flow supported by ground effect along the belly pan, will force rain water in if you provide entry by improperly stacking skins. As the speed and conditions change nothing stays the same. Hope this helps. "boatdoc"
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Old 10-21-2006, 05:07 AM   #8
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Bilge Pump

After due consideration I have decided to put a bilge pump in my belly pan.

Jim
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Old 10-21-2006, 05:45 AM   #9
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Hi Jim; Be careful, someone may take you seriously. "Boatdoc"
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Old 10-21-2006, 05:52 AM   #10
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Quote:
Originally Posted by boatdoc
Hi Jim; Be careful, someone may take you seriously. "Boatdoc"
I now think I stated it wrong. It should read.

After dew condensation I have decided to put a bilge pump in my belly pan.

Jim
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Old 10-21-2006, 06:44 AM   #11
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Reward Jim's dew consternation at your own risk.

I'm suprised no one has stripped down a small home dehumidifier and ran some drier vent flex duct to keep the majority of the basement dry... It wouldn't have to be 24/7 or even humidistat controlled. Only problem I see is reaching outrigger areas & forward of fresh water tank completly... For the money and time we are spending, even two $80 units modified for front and rear would be 'do-able'. Letsee, drain line through belly skin, unit removed from housing and relocate compressor from vertical to horizontal stacking and then suspended on vibration dampers, and add 4" flex duct to airbox to direct warmed dry air as needed..




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Old 10-21-2006, 07:11 AM   #12
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This discussion has definitely gone psychro. I think the whole topic is adiabatic. I'm going isentropic just thinking about the implications of a bilge pump.

And doesn't the collision of warm and cold air cause thunderstorms?
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Old 10-28-2006, 07:28 AM   #13
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Hey Wabbiteer; If you think your'e funny, well your'e not! "Boatdoc"
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Old 11-01-2006, 09:25 AM   #14
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boatdock, your discussion is right on. I've owned an airplane, boat, and now an Airstream. And I know you can’t fight Mother Nature. But it's like life itself, we keep trying. The airplane had many large spaces with drain holes. Part of the problem with that system was keeping the Bees from clogging the drain holes. I even had problems with ice closing off the holes. In the boat one just accepts the humidity and installs a bilge pump. In the Airstream we just want everything, insulation, cool design “looks”, and dryness. What is life without fantasy? How about this solution: A hollow belly pan with proper ventilation and equalization while we are moving down the road. Rain separators. Nanobots then could run around and devour moisture as it appears. The belly pan would have individually contoured air bags that would deploy on stopping so we would have good insulation while parked and camping. The bags would then be vacuum retracted on starting the engine of the tow vehicle allowing the air space to be clear again. Finally the belly pan unit would be so constructed so it could be lowered once every six months. During this lowering the owner could crawl into the space and clean and wax all metal surfaces. It would only ad about a ton or two to the weight of the trailer. Our wants have already added a thousand or so to the weight of the trailer since the 1950’s. When I restored my 1963 Bambi I know I made several design idea mistakes. However I was happy while I was doing it. And I am happy with the results. It will probably last longer than I will. I hope you receive this with the humor that is intended. Some of use just keep playing with Mother Nature. I think she likes it that way. I know I do.
Don

P.S. we all know who will win!
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