Do you need ditchable weight?

[Marie13]

The weights in my SM rig are against my back. No way for them to be ditchable. Think most doubles/SM divers don’t have any ditchable weight.

 

[Divin'Papaw]

Secondly you'd use your SMB. If not enough, then use your spare SMB as well. Some people think that the purpose of a SMB is a Surface Marker Buoy, but that's not so. It's a backup buoyancy, it's a lift bag, it's a signal to the surface (send up two bags on the same string, but do tell the skipper first!) and it's also a surface marker buoy.

Indeed. SMBs are very multifaceted in their usefulness. I always carry two when diving from a boat. I have a smaller and a larger. I have various options in terms of redundant buoyancy, size of marker, backup marker, etc. I don't jump off the back of a boat without one in my left pocket and one in my right. Since I dive with no ditchable weight and also no longer use a drysuit I view the redundant lift as being just as important as having a surface signaling device for the boat. I've never had to use it mind you but it only takes one time.

 

[johndiver999]

The idea that you simply have to have the capacity to ditch the amount of ballast equal to the weight of the gas in your tank....is NOT Correct. It is definitely not the right approach to a 7 mm wetsuit.

In addition, the proposition that should a diver ditch more ballast than an amount equivalent to the weight of the gas in the tank will result in an uncontrolled ascent is totally ridiculous.

If it actually were that simple, don't you think the OP would have read that in all his training manuals?

 

[inquis]

@lairdb , your revised numbers on the suit buoyancy are better. I'd encourage anyone thinking about this stuff to actually measure their suit buoyancy. A luggage/fish scale and a mesh bag makes this easy after finding enough weight to sink the suit. (Can also wrap a weight belt around the loosely rolled suit.) Measure the (submerged) bundle with and without the suit and take the difference. (This avoids the need to find exactly the right amount of weight.)

 

[Wibble]

Ditching weight really goes against the grain. The problem is lack of buoyancy and having weight that could come off and kill you doesn't work for me. It's far easier and safer to pack two (or three) SMBs than to have ditchable weight.

 

[lairdb]

@lairdb , your revised numbers on the suit buoyancy are better. I'd encourage anyone thinking about this stuff to actually measure their suit buoyancy. A luggage/fish scale and a mesh bag makes this easy after finding enough weight to sink the suit. (Can also wrap a weight belt around the loosely rolled suit.) Measure the (submerged) bundle with and without the suit and take the difference. (This avoids the need to find exactly the right amount of weight.)

Thanks, and agreed. (I'd like to correct those other sources I relied on without thinking, but.)

Using those better numbers, incidentally, I found it interesting that the contemplated diver will be at roughly -15 at roughly 33ft; if our rule of thumb max-swimmable is -15, then that's the swimmable tipping point (for that diver, with that kit.)

 

[inquis]

If it actually were that simple, don't you think the OP would have read that in all his training manuals?

As I said, bent is better than drowned. The simplistic rule of "ditch it all" will certainly prevent drowning, but weight computations are complicated to do properly due to all the variables (rig, tank size, tank material, person size, exposure suit, etc.).

the proposition that should a diver ditch more ballast than an amount equivalent to the weight of the gas in the tank will result in an uncontrolled ascent is totally ridiculous

Can you elaborate how you arrived at that conclusion? At what depth are you neutral with an empty wing & reserve tank pressure when weighted normally? How much weight are you proposing to ditch on the bottom, at say, 130 ft? What is your 7mm suit buoyancy at the surface? (For the record, not being able to stop your ascent at any point is "uncontrolled" in my book.)

 

[inquis]

if our rule of thumb max-swimmable is -15 [lb]

It might be instructional to see how much you can output in a pool without a wetsuit (assuming roughly neutral buoyancy without a suit). Have a buddy hand you weight while you fin hard enough to allow you to breath. Drop the weight when you can't keep your mouth above water.

Then reflect upon that is the amount of weight where you make ZERO progress, so you'll want to back off that threshold a bit.

 

[FishWatcher747]

The advantage of the pockets is ditchablity and convenience. They will make it easier when traveling, especially if boat diving. Get on the boat, pop in your desired weights. Reverse when you get off. Nice at home, too.

This is how I adapted my plate:View attachment 650815
Because of the single point shoulder attachment, pouches attached at the very top of the straps won't work, but the upper pouches end up a bit above the camband helping with the balance.
The lower pouches are for fixed ballast with a drysuit.
The plate attachment lowers the CM of the weights towards my body and also means that I'm not playing with the weights on the band when changing tanks.

Do you have the HOG TBCS/Comfort harness? From what I understand, they are just shoulder pads with a few straps holding the pad under the 2" webbing. Should present no issue other than affecting placement by an inch or so.

I like your setup. What size weights will go in those pockets and who makes them?

 

[lairdb]

It might be instructional to see how much you can output in a pool without a wetsuit (assuming roughly neutral buoyancy without a suit). Have a buddy hand you weight while you fin hard enough to allow you to breath. Drop the weight when you can't keep your mouth above water.

Then reflect upon that is the amount of weight where you make ZERO progress, so you'll want to back off that threshold a bit.

Yep -- considerable discussion of that in the previously mentioned @fdog thread.

(And then add safety margin -- to get above zero, plus you're injured, plus it's dark and cold, plus you're agitated, plus you have a calf cramp, plus you borrowed a reg for your pony and the WOB is getting uncomfortable, plus....)