Proper weighting

[redseal]

Hi folks! I've been enjoying surfing (no pun intended) through the various subjects on the site for weeks. Now I'd like to ask for some advice. My twin daughters and I recently got our OW certifications and have been diving every other weekend in a cool, fresh water quarry. They weigh all of 65-67 pounds and have had to carry 16-17 pounds of weight in addition to their 72AL tanks in order to get negative enough with 7mm suits. (I've had to carry 25 lbs with an 80AL for my 160 lbs). We're planning to vacation in the warm salt water of the Caribbean in a couple of weeks, and have been getting no-where trying to decide how much weight we'll all need. They will wear their 7mm tops (no body fat at 65 pounds!) and I'm wearing a 3mm full suit. Any "rule of thumb" to determine our proper amount of weight?

 

[MichaelG]

Here are the basic weight guidlines from the PADI Peak Performance Bouyancy guide.

Exposure Suit Start With
Swimsuit/Dive Skin 1-4 lbs

3mm/one piece wetsuit, 5% of body weight
shorties, jumpsuis

5mm/two piece wetsuit 10% of body weight

7mm/wet suite w/hood & 10% of body weight + 3-5 lbs
gloves

Your cylinders bouyancy characteristics affect these calculations. With the popular 80 cubic foot aluminum tank, add 5 lbs to the above.

---

That is from PADI. I am 210 lbs and needed about 14 lbs when in Jamaica wearing just a bathing suit and tee-shirt. The method above will get you close, but remember to do a bouyancy check prior to descent.

--MichaelG

 

[redseal]

Thanks MichaelG. I've seen some of the same recommendations in the AOW text, but my girls won't be wearing full 7mm, just the top/jacket plus we'll be in salt water for the first time.

I'm also curious as to whether the dive operator will give us sufficient time to check our buoyancy once we're in the water, or if it becomes a "this is the weight you SHOULD need, deal with it" situation.

 

[MichaelG]

Those guidelines are for salt-water references. I found those guidelines to be quite accurate in my requirements. It may not hurt to add a couple of more pounds on top of what it recommends. You can compensate with the additional weight with the BC, but there is no compensation for not enough weight.

More importantly, your children and your safety comes first. Make sure the dive operator knows this is your first salt-water dive and that you must do a bouyancy check first. If they are concerned about safety, they should give you the 5 minutes needed to adjust the weight properly.

P.S. check the average water temp for the carib during the time you will be going. 7mm seems a bit too much and may be uncomfortable. Not being an expert, perhaps others can give further advice. Being too hot under water is a real possibility.

-MichaelG

 

[Zept]

Do you have access to weights and a pool? If so, find out how many weights it takes to sink the entire 7mm suit, then how many it takes to sink just the jacket. Might be easiest for the girls to get neutral while wearing the entire suit, then get neutral in just the top half. All you're really interested in is the difference between the two outfits, so they don't need to wear the rest of their gear (mask and snorkel would be useful, though). The difference is the amount they can drop, assuming all other things are equal (which they might not be, if the resort doesn't have AL72s). You can do the same with your two different suits.

Someone more knowledgeable than me should be able to tell you the difference b/w an AL72 and and AL80, in terms of buoyancy.

You then need to do the fresh-to-salt conversion. Weigh yourself and all your gear, including the amount of weight you've worked out in the previous step. Multiply by 0.025. The answer is the amount of extra weight you'll need in salt water.

Around here (SE Asia), divemasters usually carry extra weight on checkout dives, in case anyone has a problem. Don't know what happens in the Caribbean, but it's always worth talking to the DM when you dive in a new environment.

Hope that helps,

Zept

 

[redseal]

Our LDS owner/operator had suggested the 7mm tops for the girls since they have such little body fat and mass; even in 80F water he felt that they would cool down fairly quickly, thought that 7mm jacket would be comfortable, and could always be unzipped if they actually became too warm.

I like the idea of seeing how much weight it takes to just sink the jacket, though. Makes sense that the same amount would apply whether there's a body in it or not!

We used 2lbs and 4lbs, respectively, in the pool for our confined water dives and that was just about right. Maybe another pound or two would have been ideal.

Thanks for the advice.

 

[SubMariner]

I disagree with the LDS that 7mm jacket is "appropriate" for 80F water. Your girls would be much better off using full 3mm suits. For extra warmpth over the core you might want to consider a polartec or aeroskin sleeveless vest, as they are virtually neutral in the water.

If they go with 7mm they will STILL require a lot of lead to be neutrally buoyant. Also, they will have very little upper body mobility with that much neoprene.

I tend to be hypothermic in the water & wear what I described in water 80F and above.

~SubMariner~

 

[FredT]

1. At 56-67 pounds those girls have to be WAY short to have any body fat at all. Fat floats, bone and muscle don’t. Toss'm into a pool in their swimsuit and mask and pass them lead until they sink with half a breath. I'd be surprised if it's more than 3 pounds. This is the base load they need to get THEM down in fresh water. (Note that this can be a negative number if they sink on their own. To figure that use a gallon jug full of water and have them add air into it a little bit at a time until they just float. Air is about 8.34 pounds positive per gallon in fresh water. To get the buoyancy needed weight the water left in the jug and subtract 8.34 pounds.) To convert this base load to seawater multiply it plus their body weight by 64.2/62.4. This is the density of seawater per cubic foot over the density of fresh water per cubic foot. This comes out to about 1.029. Subtracting out the body weight again gives the base lead load for seawater.

2. Next take a pillowcase or goody bag and put the suit top in it (_underwater_ so you don't trap any air in it) and repeat the experiment. The calculations are the same except you are adding in the weight of the suit alone. You can to the tops and bottoms separately. If the boots are REQIRED for the fins you have to fit, then do them with the fins, otherwise do them here.

3. Now do the same thing with the "standard" gear sets they'll use EXCEPT for the mask, as that is already covered in her base load.

4. Once you have those individually logged, you have 90% of the information needed to weight correctly on _any_ dive you do from now on with that gear. If you're good with a spreadsheet you can do a "check off list" of your gear and have it figure your weight for both fresh and salt water automatically once you determine what you will be taking.

Granted this is method is WAY anal, but it IS the fastest way to learn how your gear all interacts.

5. For the final piece of the puzzle the last thing you need you need is tank buoyancy information.
Check the tank spec page on Diverlink ( http://diverlink.com/gear/tankspecifications.htm ) and add in the appropriate numbers for the tanks you'll be using. Most tank specs are with buoyancy in FRESH water, and less the valve, unless otherwise noted. Valves are about a pound to a pound and a half negative. If using rental tanks in the Caribbean, unless otherwise specified by the operator, assume a Luxfer Aluminum S80 will be supplied.

Be aware the many operators will have other sizes of tanks available if you or the girls need them. I have even had operators dig up old 72s for me to use. The girls may even find they weight almost neutral with steel tanks. Generally all you need to do is ask and a good operatior will provide it if it's at all possible. BTW if the operatior will not let you do a proper buoyancy check at the dock you need to find another operator!

FT

 

[redseal]

Many thanks for all of the input. I've noticed a strong sense of camaraderie on this site along with the advice.

FredT and SubMariner, my girls are just 12yo,and are petite. The 65-67 pounds is mainly skin and muscle (swimmers and soccer players both) and the reason the LDS recommended the 7mm jackets was two-fold: their lack of body fat, and his reluctance to sell me 3mm suits that they'll probably outgrow within 6months to a year. The 7mm suits he actually bought for their rental use since most of our diving will be local and he didn't have anything small enough for them in stock.

We'll try the gallon jug of water/air trick; the local swimming pool lifeguards are getting accustomed to seeing us with "bizarre" items as it is---this should have them scratching their heads even quicker!

Regarding the dive operator, we're on a cruise, and are taking dives at Key West and Grand Cayman as shore excursions, so we won't have a choice of operator. I'm assuming that Royal Caribbean uses reputable dive charters. We're avoiding the drift dives at Cozumel until we're a bit more comfortable in the ocean.

You people are great!

 

[WreckWriter]

Originally posted by redseal
They weigh all of 65-67 pounds and have had to carry 16-17 pounds of weight in addition to their 72AL tanks in order to get negative enough with 7mm suits. (I've had to carry 25 lbs with an 80AL for my 160 lbs). We're planning to vacation in the warm salt water of the Caribbean in a couple of weeks, and have been getting no-where trying to decide how much weight we'll all need. They will wear their 7mm tops (no body fat at 65 pounds!) and I'm wearing a 3mm full suit. Any "rule of thumb" to determine our proper amount of weight?

If you come to Florida a responsible operator will probably not let them in the water with 17 lbs of weight. I wouldn't. Nor you with 25. The PADI 10% thing is too heavy. Following that I would be wearing 18 lbs instead of the 8 that I am wearing now.

When doing a buoyancy check, cross your ankles (this cuts most people's required weight in half).

A 7mm suit is wholly inapproprite for southern waters. Rent a 3mm shorty, dive with about 10 lbs (you) and about 6 lbs (them). In a full 3mm you should try a MAXIMUM of 12 for yourself, 8 for them. Even that is heavy but not hazardously so.

Overweighting is the most serious safety issue with inexperienced divers. Get the weight off and be safe.

Tom