Okay all, so we are ordering wood from Colorado and we need suggestions on getting these towers from a dry environment to a humid environment. The issues are evident and we are becoming frustrated with the end results.
Our girls duct taped quite a few silica gel desiccant packs to the inside of their tower transport box. This helped to keep the humidity low.
We thought about putting the towers in an oven and baking out a lot of the moisture and then sealing the dry tower in a plastic bag. The idea would be that they could take the dry tower out of the bag just before check-in and weighing. However, we could not find an oven big enough to try it. I think you could lose as much as 0.5g from your tower weight if you could, though.
Over the years, have a) done a number of tests to look at how much weight reduction you can get by….drying and how long it lasts, b) had ….atmospheric conditions at State or Regionals such that relative humidity was significantly higher than normal (rain/high humidity moving in), so we knew that drying could help on weigh-in weight, and c) had Nationals in a place with much higher humidity than we normally have here (in Colorado).
I’ll say up front that there’s simply no issue/concern ordering wood from Colorado, or the Atacama desert of Peru, or, oh, the Amazon rain forest, or Houston TX, where the humidity is almost always….really high. Exposed to the air, the wood does gain and loose weight from ambient humidity. The only real question/issue is how you manage exposure in a relatively short period before weighing for competition.
Second, I’ll say, it is important to stay within ‘safe’ limits reducing moisture content. We’ve used 140 F as an upper limit. Beyond that, or something close to that, you DO risk affecting glue/joint strength.
So, what have we seen/measured, and done….?
The magnitude of effect/variation is …smaller than some suggest. In a range from ~20% relative humidity to 90-ish %, we’ve never seen an….immediate effect over about 7-8%. On a 10gr structure, that’s about 0.7-0.8gr; on a, say 6gr tower, that would mean 0.4 to 0.5gr. This is from heating a large oven to 170F (the minimum setting), turning it off and with thermometer in the oven waiting till it’s down to just above 140F, and popping the structure in. The data are very similar when you put the structure in a large plastic storage box, and use a hair dryer, heating/drying the air in the box and the structure- keeping a hand near the structure, and making sure the structure is not seeing/getting air blown on it at a temperature that is uncomfortable to hold your hand in.
The duration of the effect is pretty short-lived. In a number of tests, baking/drying, and putting the dried structure immediately on a scale, you can literally see the weight increase happening (if the ambient humidity is….elevated. Looking back at data, within a minute/minute and a half, you’ve lost around half of the effect, within 4-5 minutes, it’s gone. The ….adjustment rate to ambient humidity is a little slower with higher density/larger cross section, and faster with lower density/smaller cross section, but within the range noted.
With a really air-tight box (we’ve used an Underwater Kinetics box ‘good for’ 10 meter submersion- good for smaller structures- but not big enough towers this year), drying and quickly placing in the box, along with ‘properly activated silica gel’ (baked at 325-350F for 30-45 minutes), the drying sustained itself for …multiple days. With anything short of that (a storage box with lid taped, or bag if you have one that'll fit the structure), the sustained dryness is of….shorter duration. So, my take is for, say, a trip to a competition in a high humidity location, the best way to go is doing the hair dryer treatment at the competition, immediately before going to compete.
The issue, and the bottom line in terms of benefitting from managing structure moisture content, is how you can manage the time between first exposing the structure to ambient humidity, and officially getting structure weight measured. Since the rules don’t address this… issue/technique, I’ve always a) made sure the kids understand the….dynamics of the effect- time is working against you once the box is opened, and b) advised that you want to do what you can, given the way the folk running the event are operating/running things, but only what you can- if you have the option/opportunity to get the structure on the scale before its measurements are checked, take it. If not, get the measurements done as quickly as you can. However check-in goes, by the time you’re actually testing, the structure’s moisture content will be at/very close to ambient conditions.