3 mil v 7 mil bouyancy/weighting difference

[guyharrisonphoto]

I am a Florida diver and use a 3 mil Bare reactive super-stretch. With my rig I need about 12 pounds for slightly negative weighting at the safety stop with a steel HP 100 tank.

I am going to California to dive the kelp at Anacapa and Catalina islands. I am dusting off my 7mil Mares Isotherm semi-dry for this trip, with hood. I am going to rent tanks and will get steel HP100s.

Does anyone who has made this change have advice as to how much additional weight I might need due to the difference in the suit (all else remains the same). It is 95 degrees here and I really don't want to put it on for a weighting test dive with an empty tank (but I will if I need to). Even a couple of pounds too heavy is fine, just want get some idea.

Thanks

 

[rsingler]

Try this spreadsheet to get you in the ballpark.
After entering your configuration, edit your "personal buoyancy" to make you slightly negative at your safety stop.
Then change the data to your thick suit and add weight until you get the same buoyancy.
Buoyancy, Balanced Rigs, Failures and Ditching – a comprehensive tool

Rough guess, I'd say you need to add another 12 lb.

 

[tursiops]

Try this spreadsheet to get you in the ballpark.
After entering your configuration, edit your "personal buoyancy" to make you slightly negative at your safety stop.
Then change the data to your thick suit and add weight until you get the same buoyancy.
Buoyancy, Balanced Rigs, Failures and Ditching – a comprehensive tool

Rough guess, I'd say you need to add another 12 lb.

+12 lbs to go from a 3mm to a 7mm, all other things being equal? I'd guess that is way too much, unless the suit size is very large, i.e. a lot of neoprene. Which it might be, if it actually takes 12 lbs to be neutral in a 3mm with a HP100 steel. I dive HP100s with a 5mm all the time, and only need 12-14 lbs, and add 4 more if I wear a 7mm. So I'm only up to 16-18 total for a 7mm and steel 100, not 24! But, my wetsuit size is not super large.

 

[decompression]

Put the suit in a mesh bag, place in water, add weights until it sinks.......that’s the amount of negative weight you’ll need. Add if you’ll be wearing hood/gloves/boots etc. I would say 24 lbs for a 7mm in sea water is right in the ball park.

 

[guyharrisonphoto]

Thanks everyone! The chart and this discussion gives me a good ballpark, Yes, at 12 pounds and a steel 100 with 3 mil I am overweighted to better hold bottom for photos in our strong currents here, so maybe I was overestimating what I need. I am going to go ahead and do my weight check on Saturday with a close to empty steel hp 100. I will start with 20 pounds and adjust from there.

 

[rsingler]

Yeah, I had to put a pretty big, fluffy guy into the spreadsheet to come up with 12# for a 3 mil, lol.
Glad to hear it was deliberate overweighting for photo in current. Yeah, you can get by with less.

 

[scubadada]

Hi @guyharrisonphoto

I dive with 8, 14, and 20 pounds with a 3, 5, and 7mm and an AL80. 12 pounds seems to be about right between a 3 and a 7mm.