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Thread: How much lead?

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    How much lead?

    Bought my self a new wetsuit, a 6mm O three semi dry. Went diving today and even with 12kgs of lead I was struggling to stay submerged. Before the new suit 9kgs was plenty. All my gear is the same apart from the wetsuit, my previous suit was a 5-4-3. Where am I going wrong?

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    In my experience new neoprene seems to loose a lot of bouyancy once it has done a couple of dives. Possibly things will get better after a couple of dives.

    Assuming you had no trapped gas stopping you sink and that was why you needed the extra lead

    Graham.

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    The human body has a skin area of just under 2 square metres. assuming the previous suit was an average of 4mm (being 5-4-3 and probably a bit compressed with age). That gives an extra thickness of 2mm, which gives a volume of around 4 litres. Assuming the neoprene is 1kg/litre (neoprene is 1.2kg/litre, minus whatever bubbles they've put in), means you'll need 3kg extra to sink, so going from 9kg to 12kg isn't excessive.
    Proud to be a boring health and softy crap following sissie!

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    Last edited by graham_hk; 02-12-2020 at 11:06 AM.

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    I'm always amazed when I hear about people who need double figure amounts of lead to get themselves to sink.

    I mean, we're all made of basically the same stuff with basically the same density so how on earth can there be that much variability?

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    Established TDF Member Tel's Avatar
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    Quote Originally Posted by shapeshifter View Post
    I'm always amazed when I hear about people who need double figure amounts of lead to get themselves to sink.

    I mean, we're all made of basically the same stuff with basically the same density so how on earth can there be that much variability?
    Because of what's on the inside

    I've seen many a diver that will sink like a stone in the pool and others exactly the same physical size to look at that need loads.
    The former has little internal body fat and loads of muscle. the latter the other way around. Makes a suprisingly big diference.

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    I got intrigued enough by the question to start following some links and ended up with the following very interesting paper:

    https://pdfs.semanticscholar.org/023...391.1577462203

    Long story short is that measured body density does indeed have a surprising amount of variability to it: in the sample of 173 adult males, densities from 1.017g/cm3 up to 1.060g/cm3 were found.

    I remain somewhat sceptical that these numbers explain the difference in (perceived) amount of required lead though, since the measured variation in density within the same age group is much, much smaller.

    If we assume that two guys have identical equipment then we can measure the difference in their weighting requirements my dropping them in a pool in their swimming trunks and handing them 1kg weights until they sink. For me (scrawny), that'd be no more than 2kg. Without going to the extremes of BMI are there really people who'd still be floating with 7kg of lead in their hands?

    Quote Originally Posted by Tel View Post
    Because of what's on the inside

    I've seen many a diver that will sink like a stone in the pool and others exactly the same physical size to look at that need loads.
    The former has little internal body fat and loads of muscle. the latter the other way around. Makes a suprisingly big diference.
    Last edited by shapeshifter; 27-12-2019 at 03:15 PM.

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    Established TDF Member Energy58's Avatar
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    Quote Originally Posted by shapeshifter View Post
    I got intrigued enough by the question to start following some links and ended up with the following very interesting paper:

    https://pdfs.semanticscholar.org/023...391.1577462203

    Long story short is that measured body density does indeed have a surprising amount of variability to it: in the sample of 173 adult males, densities from 1.017g/cm3 up to 1.060g/cm3 were found.

    I remain somewhat sceptical that these numbers explain the difference in (perceived) amount of required lead though, since the measured variation in density within the same age group is much, much smaller.

    If we assume that two guys have identical equipment then we can measure the difference in their weighting requirements my dropping them in a pool in their swimming trunks and handing them 1kg weights until they sink. For me (scrawny), that'd be no more than 2kg. Without going to the extremes of BMI are there really people who'd still be floating with 7kg of lead in their hands?
    Between someone of my size - 5'11" with normal BMI - to super skinny person will have a variation of about 4kg in buoyancy. The rest is how much breath they are holding. The guys that need masses of extra lead are either really fat lads or do not exhale...

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    And don't forget that the whippets will need correspondingly less neoprene to go round themselves.

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    I'm 5'7" and fairly scrawny, and in my trunks, 2Kg would sink me. A back-of-the-envelope calculation tells me that each 10Kg of extra fat would add about 1kg of lead to that (this coincides with my personal rule of thumb for weighting beginners).

    I'm guessing that - except for edge cases - these double digit weightings are majoritarily caused by unconscious breath-holding during weight tests.





    Quote Originally Posted by Energy58 View Post
    Between someone of my size - 5'11" with normal BMI - to super skinny person will have a variation of about 4kg in buoyancy. The rest is how much breath they are holding. The guys that need masses of extra lead are either really fat lads or do not exhale...


 
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