I weight 168 lbs I had a farmer John 7mil and abou 18 lbs if weight, the instructor narrowed it down to 16.5 and then he told me that because I couldn't' get neutral at 15 ft. I would have to have 17 lbs so I am going to the pool weds to see, I will let you know, thanks alot
Yeah, a 7mm suit (particulary a farmer john) is an awful lot of neoprene, which affects bouyancy an awful lot -- compresseing as you go deeper (decreasing buoyancy) and then expanding again as you go shallower (increasing buoyancy).
I've never dived at Dutch Springs, but I'd personally probably be comfortable with a 5mm full suit with hood and maybe thin gloves.
And you were diving with
much less neoprene in the Bahamas, right? Then those neoprene buoyancy fluctuations would have made
much less of a difference, making it that much easier to achieve neutral buoyancy at any given depth.
As far as how much weight you need, it doesn't sound as if you were horribly over-weighted.
It mostly depends on your body type, and a bit on what kind of tank you use (mostly composition, AL or steel). The only way to tell is by doing a good weight check in the water. People have some variations, but the classic way is at the end of a dive with 500 psi in your tank. With lungs halfway full, you should float just a eye level. and start to sink when you let out your breath completely, and float again when you inhale.
It's possible to do a weight check at the beginning of dive with a full tank, but then you'd have to add about 5 lb of weight to compensate for the weight/density of the air in your tank. Round up to the nearest pound. Plus I personally like to be balanced right-to-left.
As we all discussed above, if you
were significantly over-weighted, the large air bubble you'd need to counteract that in your BC, expanding and contracting, would be another factor making it difficult to achieve neutral buoyancy.
But I suspect in your case it's mostly the thick neoprene.
Yeah, a pool session will be a tremendous help in checking all this out. Doing a good weight check, and practicing achieving neutral buoyancy in shallow water. That's where it's toughest, because of the relative differences in pressure.
Make sure you wear the exact same configuration (neoprene, tank) as when you're actually diving.
Let us know how it goes!!