Estimating weight needed

[Wheatondiver]

Recently purchased wetsuits and trying to estimate weight needed.

1. 170 lb male in decent shape
2. approximately 100 lb boy. Since he is 11, we are limited to 40 feet.

Previously:
1. 18 lbs of lead. 5 mm jumpsuit (rental), hood, gloves, boots. Steel tank (rental). Freshwater. This was about right. Padi recommends 10% body weight which would be 17 lbs. Used 18 lbs.

2. 16 lbs of lead. 5/4/3 jumpsuit (rental), hood, gloves, boot, 2/5mm shorty underneath to add bulk and fill out wetsuit. Steel tank (rental). Freshwater. Son a little struggle to start down, but once down was about right. Padi recommended 10% which would be 10 lbs. Used 16 lbs.

Now:
1. Purchase 7MM farmer john and 7MM step in Henderson wetsuit. Will be using hood and boots. Water is warmer and gloves not necessary. Renting an aluminum 80. Padi book suggests 10% body weight plus 3-5 for 7MM wetsuit and 5 for aluminum 80. This would be about 25 - 27 lbs. This seems a little heavy.

2. PUrchased 4/3 jumpsuit Henderson Hyperflex wetsuit and a 5/3 hood/vest. Will be using boots. Renting an aluminum 80. Padi book suggest 10% body weight plus 5 for aluminum 80. This would be about 15 lbs. This seems a little light.

If my calculations are correct, then I will need to pick up more weight. We both have the pouch weight belts so changing out weight is not too difficult, but would like to get close before we start the dive on Sunday afternoon. We are planning on doing one dive Sunday, so we won't have the chance to adjust under the same conditions on the same day. I would like to be close since a little heavy can be adjusted with a little air in the BC. A little light can be adjusted with wetsuit squeeze at depth eventhough it is 40 feet or less.

Any and all suggestions are welcomed.

 

[1_T_Submariner]

Just a guess but, add a few to start on #2. A proper in water weight check will be needed I think. You wouldn't want to head out with less than say 50lbs and leave some on the boat.

 

[Wheatondiver]

An update.

We will be at a quarry. I thought estimate. Get in water just over our heads to check. If we need to get rid of some, we can go to shore and dump some. If we need more, we can go to shore and pick up some.

After I put on 16 lbs and my son had 14 lbs on in May, we had about 16 left over. I had 4, 2, 2, 4, 4. My son had 3, 3, 2, 3, 3. We had 5, 5, 2, and 4. I think I will need to pick up some more lead before Sunday.

 

[Charlie99]

Any and all suggestions are welcomed.

Next time you use a steel tank, note which the manufacturer and model. There is a wide variance in buoyancy between the various steel tanks, even those of the same size.

Not knowing what tank you were using makes the info on how much lead you used on previous dives virtually useless.

If you DO know the specific steel tank you used, http://www.huronscuba.com/equipment/scubaCylinderSpecification.html will give you the "empty buoyancy" spec. The two most common AL80 are both about 4 pounds positively buoyant. The difference between the empty buoyancy of the two tanks needs to be compensated for with that amount of lead on your belt.

I would like to be close since a little heavy can be adjusted with a little air in the BC. A little light can be adjusted with wetsuit squeeze at depth eventhough it is 40 feet or less.

Your first statement is correct, but if you are a bit light you will do fine at depth, but then go into an uncontrolled ascent as you come back up. Not good.

You really need to do a real weight check. You can check your weight with other than an empty tank if you account for the weight of the air. In an AL80 the air in the tank weighs about 1 pound for every 500psi --- so if you adjust weighting with a full 3000psi in the tank, just add another 5 or 6 pounds and you'll be good to go.

You'll need to check your weighting again after you've done 10 or so dives to 80' or more. This will crush your wetsuit a bit, making it less buoyant.

Don't forget to keep those hand and feet still, and exhale FULLY when you are trying to descend.