My last 3 BC's have all been back inflations. I had a Malibu, a Black Diamond and now my BP/W. Here is why you were floating on your face:
1 Most instructors have students dive overweight, and leave weight and trim to be learned later. I bet you are diving with at least 10% of your body weight, right?
2 Most students tend to dive heavy anyway. They like to "get down quicker".
3 When you do this, you are forced to add air to your BC to be neutral or float.
4 The combo of extra weight and more air= float on face
You should only be wearing the weight required for the dive, no more. If you have access to a pool, here is how to do it:
First, enter the pool wearing nothing but a mask, snorkle and swimsuit. Keep picking up weight until you start to sink when motionless. That is the weight for you.
Now take your wetsuit and place it on the bottom of the shallow end, use weight to hold it down. Remove 1 pound at a time until it starts to float. Add a pound back on. This is the weight for the wetsuit.
Add 4 pounds for aluminum tanks (AL80).
That is what you need for fresh water. Add weight equal to 2 1/2% of your body weight for salt water.
In the beginning, I would even try adding 1 or 2 pounds to the above numbers, until you get used to it.
