Weight checks on charter(from cruise ship)
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high_order1
Contributor
I realize this is humor, but
My brother had a pool that used saltwater. Wonder how close that might mimic seawater for the purposes of trim management?
My brother had a pool that used saltwater. Wonder how close that might mimic seawater for the purposes of trim management?
Not very close. Seawater has about 1200% more salt.
WillieJustice
Contributor
As a point of comparison only, I recently dove in a cenote (fresh water) and in the ocean. I used no weight in the cenote and 8 pounds on the reef. I may have been OK with 6 but didn't want to push it. I use a whole lot more at home in a drysuit. That is not fully dialed in yet, but somewhere between 24 and 28 has been working. It may get down closer to 22, but I don't want to push it and have a problem. Full disclaimer: I write this with a whole 41 dives done.
Lot of guesswork in this thread, some on target, some not.
Use this spreadsheet and get really close.
scubaboard.com
If you know the weight needed in freshwater, add 3% of your weight (you and your gear) to adjust for salt water....typically 6 lbs.
Use this spreadsheet and get really close.
Info - Optimal Buoyancy Computer
The Optimal Buoyancy Computer A tool to help nail buoyancy and improve safety, before you splash 1) How much lead should I carry with my new wetsuit? 2) How big a wing should I buy? 3) Will my BCD support my lead, both at the surface and when my wetsuit is compressed at depth? 4) Will my BCD...
While there are some on this board that do not find divebuddy.com to be accurate for them, it works great for me. You can also look at the buoyancy calculator by @rsingler here on SB, which is highly rated by SB members. I personally have not had great luck with DMs’ estimations of how much weight I need, as they generally underestimate my weight requirements.
Edit: After typing, I see @tursiops already posted the link.
Edit: After typing, I see @tursiops already posted the link.
I appreciate the call outs, but for seawater resort diving with rental equipment, we can make some assumptions:
1) a jacket bcd with 0 buoyancy when wet.
2) first stage buoyancy -1.5 #
3) Full tank AL80 -2 # (because +4# tank; -6# air)
4) personal buoyancy (-2# to +4# for body fat)
5) an old rental 5mm wetsuit (+10 to +15# buoyancy AT THE SURFACE)
Since you want to be neutral at your safety stop with 700psi left, we need to consider
1) gas used (+4# buoyancy)
2) suit compression at 15ft (-4# buoyancy)
When we do the math, you only need 6-12 lb. lead, at the surface, at the beginning of the dive to float at eye level with that extra -4# of gas for the dive, and NO air in your bcd.
At 15 feet with a 700psi tank, you're neutral.
Therefore, 6-12 pounds needed, for NO body fat to "a little fluffy". Maybe a little more for extra fluffy.
All logical, albeit a little too detailed.
But if you do the PADI "10% of body weight" shortcut, you end up with 15-20# "required". Overweighted, as usual.
Except that inexperienced divers are less relaxed. And anxiety keeps an extra 1-2 liters of air in your lungs ( +2 to +4.5 #). So PADI isn't "wrong". They just don't presume either experience, or attention to detail. Which generates all the the PADI-bashing. But they're not "wrong". They just assume you're not paying attention.
Short answer? Take what the DM recommends and see what your buoyancy is at the beginning of the dive with an empty bcd. If you float at eye level, perfect! If you're sinking with zero bcd air, hand back 2-4#. Obviously, to relax awaiting dive start, add a little air to your bcd to float with your head completely out of the water.
Now dump your bcd, exhale fully and wait a few seconds. You'll slowly sink, and suit compression will allow you to stay negative to descend. Add bcd air as needed to stay neutral during the dive.
At the end of the dive with a "floaty" tank, your suit compression will match it and you'll be neutral at the safety stop with ZERO air in your bcd.
Inhale, and slowly float to the surface where you're now +4# due to suit reexpansion. Add a little bcd air for safety and wait for pickup.
1) a jacket bcd with 0 buoyancy when wet.
2) first stage buoyancy -1.5 #
3) Full tank AL80 -2 # (because +4# tank; -6# air)
4) personal buoyancy (-2# to +4# for body fat)
5) an old rental 5mm wetsuit (+10 to +15# buoyancy AT THE SURFACE)
Since you want to be neutral at your safety stop with 700psi left, we need to consider
1) gas used (+4# buoyancy)
2) suit compression at 15ft (-4# buoyancy)
When we do the math, you only need 6-12 lb. lead, at the surface, at the beginning of the dive to float at eye level with that extra -4# of gas for the dive, and NO air in your bcd.
At 15 feet with a 700psi tank, you're neutral.
Therefore, 6-12 pounds needed, for NO body fat to "a little fluffy". Maybe a little more for extra fluffy.
All logical, albeit a little too detailed.
But if you do the PADI "10% of body weight" shortcut, you end up with 15-20# "required". Overweighted, as usual.
Except that inexperienced divers are less relaxed. And anxiety keeps an extra 1-2 liters of air in your lungs ( +2 to +4.5 #). So PADI isn't "wrong". They just don't presume either experience, or attention to detail. Which generates all the the PADI-bashing. But they're not "wrong". They just assume you're not paying attention.
Short answer? Take what the DM recommends and see what your buoyancy is at the beginning of the dive with an empty bcd. If you float at eye level, perfect! If you're sinking with zero bcd air, hand back 2-4#. Obviously, to relax awaiting dive start, add a little air to your bcd to float with your head completely out of the water.
Now dump your bcd, exhale fully and wait a few seconds. You'll slowly sink, and suit compression will allow you to stay negative to descend. Add bcd air as needed to stay neutral during the dive.
At the end of the dive with a "floaty" tank, your suit compression will match it and you'll be neutral at the safety stop with ZERO air in your bcd.
Inhale, and slowly float to the surface where you're now +4# due to suit reexpansion. Add a little bcd air for safety and wait for pickup.
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Wow that was simple, so wear 10% of your body weight in lead and go diving
On this cruise not the next cruise
Thanks for that
On this cruise not the next cruise
Thanks for that
WillieJustice
Contributor
So you will be nervous and floaty this dive and happy the next one? Ah-ha!
I am a little amazed that PADI recommends that much for warm water. Even as a nervous newbie, I haven't used more than 16 lbs in warm water and I weigh 190 with a fairly low fat content for an old man.
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