Tanks, Weights, Aluminum vs Steel

[furym]

So I have a dive coming up and want to get reasonably close on my weight. Not sink like a rock or bob helplessly on the surface.
I use 10 lbs with aluminum 80s and a 3 mil suit in fresh water. I used 14 lbs with a 3 mil shorty and aluminum 80 in salt water.
I will be diving Steel 117s in salt water with a 5 mil suit. What should my starting weight be? It was suggested 8 lbs but I am newly back to diving and don’t have a lot of recent data on my weights for comparison.
I know the steel 117 will count for some weight added while the 5 mil suit will require some weight added. I am not sure where they might balance out. What say the experts?

 

[rsingler]

Try here:
Optimal Buoyancy Computer
Adjust the tool so it matches your salt water shorty requirement, then switch suit and tank.

 

[furym]

Try here:
Optimal Buoyancy Computer
Adjust the tool so it matches your salt water shorty requirement, then switch suit and tank.

Thanks, but the spreadsheet is not playing nice with my MacBook. I will have to try that one in a few weeks when I am back on my work computer.

 

[rsingler]

Well, a Faber FX-117 is about zero buoyant empty. So that's four pounds less than your AL-80, but a full length 5mm wetsuit is about 8# more buoyant than a 3mm shorty, so that suggests you'd need 17#, not 8#.

But if your tank is heavy when empty (-2 to -7# is common), then you can shave that off the #17 I just suggested.

Same bcd? Zero buoyant?

 

[furym]

Well, a Faber FX-117 is about zero buoyant empty. So that's four pounds less than your AL-80, but a full length 5mm wetsuit is about 8# more buoyant than a 3mm shorty, so that suggests you'd need 17#, not 8#.

But if your tank is heavy when empty (-2 to -7# is common), then you can shave that off the #17 I just suggested.

Same bcd? Zero buoyant?

All different rental gear. They sent me with 14 lbs. I hope it’s enough.

 

[runsongas]

14 sounds reasonable, but maybe ask for another 2 just in case.

 

[Oz Chris]

When I'm travelling to warm places I use 10lbs with an AL80 and 3mm wetsuit. At home I also use 10lbs with an HP100 steel and a 5mm wetsuit (the two changes pretty much cancel each other out).

 

[furym]

So, I jumped in with the 14 lbs and about sank right away. Off loaded the two 3 pounders and made the two dives with 8 lbs. No trouble getting down with those but a little light for the safety stop in free water. The visibility was so low we never found the anchor line to ascend and had to do our safety stops without the aid of the bar under the boat. Being in rental gear it was a little difficult finding my right trim that day. I can’t wait to be able to invest in my own gear that I can trim out properly.

 

[W W Meixner]

So I have a dive coming up and want to get reasonably close on my weight. Not sink like a rock or bob helplessly on the surface.
I use 10 lbs with aluminum 80s and a 3 mil suit in fresh water. I used 14 lbs with a 3 mil shorty and aluminum 80 in salt water.
I will be diving Steel 117s in salt water with a 5 mil suit. What should my starting weight be? It was suggested 8 lbs but I am newly back to diving and don’t have a lot of recent data on my weights for comparison.
I know the steel 117 will count for some weight added while the 5 mil suit will require some weight added. I am not sure where they might balance out. What say the experts?

F...

If you're in NC...you should have quick easy access to more than a few LDS's...and shore dive areas...

Suggest you and a friend...dial in your buoyancy in the shallows...with the gear you will be diving with on your upcoming dive...rent or borrow a HP steel 117...and a comparable suit...

Follow your OW training...perform your buoyancy check...starting with the smallest weights first...

You should be dialed in...in less than five minutes...

Avoid calculation methods...too many variables...

Best...

W...

 

[rsingler]

So, I jumped in with the 14 lbs and about sank right away. Off loaded the two 3 pounders and made the two dives with 8 lbs. No trouble getting down with those but a little light for the safety stop in free water.

It's important to keep in mind the weight of the air you consumed. You are supposed to be heavy at the beginning of the dive. With a 117, breathed down to 750 psi, you consumed ~8lb of air!
So after dumping 6 lb because you felt heavy, it makes sense that you are light at the end.
Keep in mind the object of the buoyancy check: to be neutral at 15' at the end of the dive, accounting for a little wetsuit compression.

To do a buoyancy check with a full tank (in a thin wetsuit, at least) pull off weight until you float at eye level, then ADD BACK the amount of weight you will consume during the dive: about 5# for an AL80, about 8# for your 117.