This is my first year going to Nationals, so I have a few questions;
I understand that the rules for size parameters are followed very strictly at Nationals, but I was wondering, what about the "The bottle can't have any scratches on it" rule? To put that another way, how deep/big can a scratch/scuff be until you get DQ'ed?
Also, do you have to mark which label came from which rocket? I'm assuming no (based on the rules), but better safe then sorry!
And finally, I've been using duct tape to attach the fins(I used balsa at States, but I'm going to switch to foam board) because it's pretty strong, but is it too heavy?
Should I be using packing tape instead? What have you guys found works the best?
I'm from Idaho, and the rules are...
Well, let's just say...
They're not followed as strictly as they could be...
I'm completly sorry I didn't see this earlier. I believe I can help you a lot.
For the bottle scratches, I believe that anything that might possibly comprimise the structual integrity of the bottle can be called out by the judge, and possibly get you DQed.
But on the other hand, it's difficult to replicate rocket results when you switch bottles. This is really a question up to decide on. Would you call out the bottle because of the scratch? or do you think that a scratch could weaken the bottle? if so, then I suggest that you replace your bottle with an Identical bottle, but make sure that you practice with this new bottle if you change it.
For the labels, I think all judges look for is the "Carbonated Beverage" label, and sometimes a rough corrolation between bottle and label. What I mean, is that they can see if you used a 2 liter coke label for a 1 liter bottle and so on so forth.
If you are using duct tape to attach fins, I suggest that you use the least amount possible, or switch to packaging tape. Attaching fins is really the only place where you should use duct tape. If you have it anywhere else on the rocket, you should switch to packaging tape for weight reduction. If you can, even try packaging tape on the fins, but test to see if it's strong enough to hold them in place before you compete.
The materials you use on your fins seems a bit iffy though. Balsa is a bad material for rockets in general, and I'm glad you noticed that. Foam board might work, but I have a better, weight friendly solution you should maybe check out. I suggest you get Corrugated Plastic boards, and 0.007 inch plastic film to make a sort of hybrid material fin design.
My design consists of a Trapezoid shaped fin, made out of a parallelogram shaped piece of corrugated plastic in the front (make sure the holes are parallel to the leading edge)
and a triangle of flimsy plastic film on the back. The film is pulled taut from being taped between the bottle and the corrugated plastic leading edge. once you have this down, I would pinch the front of the corrugated plastic into a point for better aerodynamics (hence why I suggest that the holes be parallel to the leading edge.) Then tape this onto the bottle.
since I don't know the overall design of your rocket, I suggest that you play around with this design, and work out which variation of this design works best on your rocket.
Good luck at nationals, and happy flying!