let the insanity begin

Sorry guys, I guess I lied when I said the pvc angle is 3/4" in each direction. I was just looking at my USP catalogue and their website. The smallest size they have listed is 1" x 1" x 1/8". That would give me a 1 1/4" joint. Should be adequate, right?

1/2" square stock is quite a bit cheaper than the angle. That would give me a 3/4" joint and I wouldn't have to worry about mitering where they meet. Any thoughts on the strength of that?

For the cross braces, do y'all think the angle would work too (I could glue short pieces of the angle to the sides and then glue the cross braces to the short pieces to get a 1" joint there), or would it be better to go with some square stock or round stock (round is cheapest) to give a bigger contact area and just glue it directly to the sides?
 
I am puzzled a little bit.. if you are worried about shadows, why did you choose non light transfering sides? i know the cost was right.. but is that not a small sacrifice, if indeed that is a concern you are not willing to compromise on. [as pvc is not as reflective as glass underwater..... [see diagram] in adition to using that reflective properties of glass.... i believe you could have used reflective alum. NEXT to the tanks with glass.. to make the sunlight hit the tanks from the sides.... [and get anouter 30% extra light in the tanks [glass or acrylic would stop some, but not all the beneficitial rays] .. let alone, it would hit up the lower overhangs on the corals.. and they would grow more.. basically a reflector/ light collector wiht the tank in the center not the light bulb.. does the reverse function that a light reflector does..


just to show you what i do in my tank..... i use reflections in my tank to get a wider variety of angles...

note poished alum. works better than a mirror...

20reflections.gif
 
In terms of deflection the 1/2 would be about 1/2 as good.

1/2 thick * 1/2 ^3 = 1/16
1/8 thick * 1^3 = 1/8

Also in terms of glue joint it would be 1/2 as good because you have a 1/2 joint instead of 1" joint.

The solid would alow you to join the sides with small screws as well as glue.

I think I would go with the solid square because the ability to add some screws would make construction easier by pulling the joints tight as the glue dries.

I think the load of the cross brace might be a bit much for a 1/2" x 1/2" glue joint. You could get a strip of 2x2x1/4 angle to make some angle brakets to increase the glue surface (and spread the load on the 1/4" sheet). One piece would prob be enough to do all the tanks. you would only need (6) x 1/2" for each cross brace.
 
matt- I addressed most of those issues in a previous post concerning the cost factors, fabrication, delivery, temp stability vs volume, and amonunt of propagation space for the money.
The mirror tip looks like it might be very beneficial for a home tank.
I have seen a few tanks (and read about some) that have white sand on the bottom to uplight the corals. The pvc tanks being white will reflect SOME light around inside and was why I didn't pick gray. Clear pvc sheet is almost triple what white is.

tschopp-sounds good to me. thanks for your help on this one.

As always, I appreciate everybody's input and contributions.
 
Rick, you purchased white pvc sheets. This sounds a lot like Bomber's idea of using starboard to light the corals from below via reflective light. My guess is this is going to be good at first, but as algae (coralline or worse) grows on it, the reflective properties will deminish exponentially.

Any reinforcement in the seams is a good one. Some are better than others, if tschopp's comments are accurate. I think the square stock would be easier to work with.
 
Rick,
I was wandering about the orientation of the green house and the tanks. It looks like long side of the greenhouse goes North-South based on shadows in the pics, is this correct?

The stand you have in the picture has the long side perp to the long axis of the GH. So the long side of the tanks would be East-West?

Since we are at 40N latitude. The sun will be between 27 (winter) and 73 (summer) degrees above the southern horizon at noon. If the long axis of the tank is N-S then there will not be a pvc wall blocking the sun from getting in the tank.

On the other hand if the tank is E-W the reflection off the back wall could help light the N side of the coral.

I have no real opinoin on what is best, this just came to mind looking at matt's drawing (at first I though his virtual halide was the sun). I suspect you will have plenty of light and the real question will be what to do for shade cloth.
 
lighting

lighting

I would just like to congratulate you on getting this far and encourage you to keep going!

I am very interested in the outcome of this. I am especially interested in how much the temperature will vary with and without your heater/cooler running and if you will have to supplement blue actinic lights to compensate for the spectrum of sunlight and the shallow water.

I do know that the people who attempted this in Florida usually needed 50% shade cloths over their tanks to reduce the intensity. They seemed to have mixed results with corals becoming brown just via the sunlight.
 
melev- I agree, as time goes by, the white won't be as white anymore and will reflect less. The sides should be able to be kept reasonably clean with typical maintenance. The bottom will be partially covered with rock anyway. I haven't seen any studies done in the wild that measure the amount of uplighting corals receive, but my semi-educated guess would be not much compared to what they receive from above. I do think there is some benefit to uplighting as it helps the lower branches of a colony thrive instead of getting shaded by the upper parts, but then again, that just means it is time to frag 'em. :D

tschopp- yes, correct. the long side of the greenhouse is oriented north-south and the tanks are perpendicular to that.
That was one of Calfo's recommendations, to have the greenhouse itself oriented south (or southeast) and have the tanks perpendicular.
I'm not sure I understand what you are saying about having the tanks north south would eliminate blocking from the pvc wall. The walls of the tanks will be the same height all the way around. It seems to me that the sun would hit a two foot wall the same wether it is 7' long or 2' long.
I do agree that I will need some shade... in summer. Again according to Calfo, about 30% from May to September. I also expect to have to use some supplemental lighting over shallow water stonies (or those gaudy yellow leathers, etc.) in winter.

I been meaning to ask you..your formula for deflection seems pretty simplistic. Does it account for length of sides (longer material should bow more?), height of sides (taller material should bow more?), additional support features? Is it for the sides themselves or can it also be applied to the joints? Am I even understanding the application? Questions seem a little ignorant considering my dad works in materials research. :D


nonot8946- Thanks for the words of encouragement.
I do not expect to need actinic supplements, although I am going to have them for overhead lighting once the construction phase is completed (if ever). Having tanks a couple feet deep at a northern latitude will roughly estimate equatorial sun at a depth of 25 feet down to 45 meters. The actual light would depend on where the measurements were taken. Some areas of the ocean have turbid water and some areas are pristine.

Some corals turn brown from not enough light, others from too much.
 
rick rottet said:

tschopp- yes, correct. the long side of the greenhouse is oriented north-south and the tanks are perpendicular to that.
That was one of Calfo's recommendations, to have the greenhouse itself oriented south (or southeast) and have the tanks perpendicular.
I'm not sure I understand what you are saying about having the tanks north south would eliminate blocking from the pvc wall. The walls of the tanks will be the same height all the way around. It seems to me that the sun would hit a two foot wall the same wether it is 7' long or 2' long.
I do agree that I will need some shade... in summer. Again according to Calfo, about 30% from May to September. I also expect to have to use some supplemental lighting over shallow water stonies (or those gaudy yellow leathers, etc.) in winter.

I been meaning to ask you..your formula for deflection seems pretty simplistic. Does it account for length of sides (longer material should bow more?), height of sides (taller material should bow more?), additional support features? Is it for the sides themselves or can it also be applied to the joints? Am I even understanding the application? Questions seem a little ignorant considering my dad works in materials research. :D
Click to expand...

About the tanks being N-S vs E-W. If the sun is 45 degrees above the horizon. The 2' tank wall will cast a shadow of 2' at the bottom of the tank, or 1' half way down the tank where the corals will be. If the tank is E-W (at 1/2 way down) you will have 1' x 7' in the sun and the rest in the shade. If the tank is N-S you will have 2' x 6' in the sun and the rest in the shade.

With the N-S tanks the coral will not get much light on the N side. With E-W tanks you will get reflection off the wall N of the corals that will help to light the N side.

The deflection formula was kept overly simple. The formula I was using is based on deflection of a beam that is not anchored at the ends. Clearly this is not the case you have for any of the joints or the deflection of the top rim. It can be used to make some simple comparisons and ilustrate some concepts.

Deflection at the middle of a beam is given by:
D = F L^3/ (T X H^3)

F is a material property that I have not looked up for PVC. L is the length of the beam in your case 7'. T is the thickness of the beam (for a 2x6 it is 2"). H is the height of the beam (6" for a 2x6). If you are making comparisons where some of the things stay the same and some change then you can make an easy comparison between the 2. For example, the deflection of the rim. The geometry of the tank is the same, the material is the same (pvc), legth of the tank is the same. The thing that changed was T and H all the other stuff is the same. The comparison does not tell you what the deflection will be only that one type will deflect 1/2 as much as the other.

I hope you did not interpret the numbers 1/16 and 1/8 as deflections in inches, they are not. They were only to point out that the 1/2" bar is 1/2 as good as the 1" EL.

To get the actual deflection you would need to consider the entire system, panels, x-brace, corner brace, etc. This is non-trivial and why I sugjest you build one and see how you like it. If you are happy then build the other 19, if not add more support until you are.

For my tank I did not do a full static caculation, I made some simplifications that would guarantee an over built tank. I did calculate the actual deflection in the wood on the top rim, but I only considered the force it would need to support, I did not include the ability of the glass to handle some of the deflection. Since a 3/4" pannel of glass can certainly help resist the deflection the result is an over built tank. I did the initial fill in my house, I could not risk having 500 gal let loose in the family room.

The length is an important thing. Having ran the numbers on my 8' tank I would say you will need x-brace or some serious bracing on the 7' length. If you put 2 x-brace in the tank is effectivly then 2.3' long x 2' high.
 
"Since we are at 40N latitude. The sun will be between 27 (winter) and 73 (summer)"


random thought...

remember Snell's Law.. when talking about shadows.. the light will not enter the tank at the same angle it does in the air.. as seen by these pictures...

so technically, a support on the inside of the tank rather than in the senter would probably do less harm in causing shadows than if the light was passing through only air...

Exer02demo.gif



Fig4b.jpg
 
Can I just say "Oh... My.... God!" You guys are blowing me away with the mathematics and physics. I'm amazed and impressed.
 
Good point about refraction as the light enters the water, So the shadow will be less than 1' half way down and less than 2' at the bottom.

The light will go from 45 degrees to 32 degrees from vert and the shadow at 1/2 way will only be 7.5"
 
matt ~ whats the ratio between the incident angle and the refractive angle in that diagram?

IIRC the ratio always is consistent, regardless of the angle of the light source...?
 
Snell's Law: n1 sin(t1) = n2 sin (t2)

where n is the index of refraction : 1 for air approx 1.33 for water
t1 and t2 is the angle normal to the surface.

So, no the ratio does not stay costant it is a function of the incoming angle.
 
in the small angle approximation for sin (sin(t) = t) it will be a constant ratio, but this is only true for small angles
 
this is what is responsible for items in the water seeming close when they are further away in auctuality.. [like if you are wading in a pond]


i would send you to this. yes, the angle will change as the day changes.. [and as the seasons chage as well] use this handy calculator ... if you are worrie,d i woudl use it to calculate estimates at noon, and maybe 2 to 4 other times of the day... it is mroe the awareness that a shadow when a tank is dry is gogin to be a lot worse and obstructive than when the tank is full.. assuming the light is entering at an angle [which it always will]

http://www.ndt-ed.org/EducationResources/CommunityCollege/Ultrasonics/Physics/refractionsnells.htm
http://www.physics.nwu.edu/ugrad/vpl/optics/snell.html

wrong link earlier

the only time the beam will enter straight assuming no surface disruption would be at high noon, when the sun is direfctly overhead [but that dont' happen here]

can you tell my dad is a particle/ quantum physicist :) i can't get this type of stuff out of my head!!!!
 
Last edited:
Angle of Incidence (degrees) Angle of Refraction (degrees)
0.00 0.00
5.00 3.76
10.0 7.50
15.0 11.2
20.0 14.9
25.0 18.5
30.0 22.1
35.0 25.5
40.0 28.9
45.0 32.1
50.0 35.2
55.0 38.0
60.0 40.6
65.0 43.0
70.0 45.0
75.0 46.6
80.0 47.8
85.0 48.5


i also found this interesting..

Crictical angle for water = 48.8 degrees

Light within the 48.8 degree cone
is detected by fish, while nothing in the
air outside that cone can be seen.
The only light reaching the fish outside
the cone is that light (not shown) which
is reflected off the bottom of the pool.

coneofdarknessforfish.jpg
 
:uzi: give me this thread and no one gets hurt

:rolleyes:





he said he wanted this stuff..



:p

i m p o r t a n t "IMEO" lol given some one is relying on a changing light source.


the rest of the world----------> :sleep:



sorry about the typos.. i type fast..




and believe it or not i teach music, not science :)
 
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