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So what's the difference between 7 lbs of lead on your belt or in your BCD and a tank that's 7 lbs heavier? Is it just about moving the weight elsewhere?
Who says the tank is 7 lbs heavier? AL80s are about 31.5 lbs empty, worthington X-7 is listed at 33 lbs. The tank is 7 lbs less buoyant, not heavier on land. Think of it this way, the AL80 is 31.5, but you need roughly 4 lbs to sink it, so your total on land weight is 35.5 lbs, where the X-7 weighs 33, but you can remove 2.5 in lead, leaving you with 30.5 lbs, or about 5 lbs less than the AL80. Those are approximations, not exact figures.
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Originally Posted by jebmobile
With an AL80, I use 4lbs of lead in saltwater and 8lbs if I have a fully 3mm suit on. That's probably below average compared to many. Would a steel HP100 be too heavy?
You'd be a couple of pounds heavy without the wetsuit. Not the end of the world; I'm actually a pound or two heavy with the HP100 in a 3 mil. It's worth it.
You might try the faber FX100, it's supposedly 1.5 negative empty. Might be a bit better for you.
Another weigh to look at it (pun intended) is to examine the density of the materials. The more dense the material (e.g. lead) the better ballast it makes. That's why we use it for ballast, its very dense relative to water.
Steel is relatively dense and even accounting for an empty tank you have some ballast weight left over so you can reduce you lead ballast a bit. It also helps that steel is stronger and so the side walls of the tank are thinner than AL (needing less material) and on land the weight is close to the same.
Al is less dense, so much that you need to add lead to make the empty tank neutral. It is cheaper and less prone to rust, so it wins the popularity poll despite its buoyancy issue.
If you believe in having enough ditchable weight as I do, then yes the HP100 would be too heavy, as it would leave you with only 1-2 lbs of lead with the 3 mm suit.
First, I've got to ask do you really need ditch-able weight? Assuming you are not overweight, shouldn't you only be a few lbs negative overall throughout the majority of your dive?
When diving in shallow freshwater (15-20ft - 5 mil suit), ss backplate, and AL 80. I generally do you not use the BC at all (that's not to say I don't have the wing on, that is to say that I don't inflate it at all). When you are close to neutral it's just like swimming up your own body weight, so I don't really see where ditching weight would benefit me at all in this situation.
I am also planning on making the move to steel. My understanding is that you start the dive negative, and end the dive slightly negative or close to neutral if you plan things right, and as an added bonus your aggregate weight is less. With AL you start the dive negative, and you end the dive slightly negative or close to neutral if you plan things right, but you are carrying extra weight on the belt to accommodate the extra buoyancy of the AL tank, so your aggregate weight is more when compared to a steel tank diver.
I am currently diving a SS backplate so I'll have to switch to an AL backplate when I go to steel. Looking to go with HP100s.
please correct me if I am wrong as I am still very new at this