To learn how the density of drift cards compares with the density of some oil products, we made some simple calculations.
1. We weighed 20 of our drift cards. Surprisingly, the weight of the cards varied from 26.5 grams to 34.5 grams!
2. We then measured the dimensions of the 20 drift cards. The dimensions ranged as follows:
Using the weight and dimension ranges above, we calculated the following densities:
26.5 g/(15.0 * 9.9 * .32) = 26.5/47.5 = 0.56 g/cc = 121 API
34.5 g/(14.8 * 9.8 * .3) = 34.5/43.5 = 0.79 g/cc = 47 API
The average density of the drift cards was about 0.67 g/cc = 79.7 API
Comparing the drift card's density with the following oil products, we noted that its density is about the same as that of gasoline.
| Product | Density (g/cc)* | API* |
|---|---|---|
| Diesel Fuel | 0.83 - 0.88 | 39 - 30 |
| Gasoline | 0.67 - 0.75 | 79 - 57 |
| Alaska North Slope Crude | 0.90 | 27 |
1. The drift cards are light, and they float quite well. The heaviest of the cards will float like gasoline. The implications of these characteristics are that the wind will play a larger role in how the cards move than it would for oil products.
2. The drift cards are flat, so they don't have much "sail" (not much of the object is out of the water). We would guess that the windage (the influence of the wind) on the cards would be between 3% and 5%. For oil products, windage would be between 1% and 4%.
It's interesting to compare the behavior of drift cards in the water with the behavior of oil products in the water. Unfortunately, we don't know the density, amount of "sail," etc. for other kinds of debris, so we can't compare the drift cards with drift wood, Styrofoam cups, paper, etc.
