Ditchable weights...are they needed and is there a minimum?

[BlueDevil]

Have a look at a White's Fusion Drysuit - plenty of threads here on ScubaBoard about them

 

[halocline]

I would start by taking the weight plate off, see what that does. You might be better off with an AL or kydex plate for that tank. The steel tank you're using is about 14lbs more negative when filled than the AL 80 you were using. So you'll have drop 14lbs to have the same buoyancy at the beginning of your dive. The two tanks are about 11.5 lbs different empty, so actually what you would do is drop 11 or 12 lbs and deal with being a few lbs more negative at the beginning of the dive.

So, if you take your weight plate off, then you drop another 7 lbs from the belt and you should be okay, at least theoretically. You're still going to be heavier at the surface at the beginning of the dive. There's no escaping that, because the buoyancy swing in the steel tank is greater due to the increased gas weight.

 

[Texasdivechick]

This is a good question and one that I have also considered. I do not dive the same rig as the OP, but when I've asked about a minimum amount of ditchable weight, I always get opinions from two opposing camps. I use a back inflate BC, AL 80, 3 ml wetsuit, fresh water, and Slipstream fins. I generally use 4-6 lbs of weight, all located in my trim/cam pockets. If diving in salt water or with a thicker wetsuit, I will put MOST of the weight in the trim pocket (6-8 lbs) and only about 2-4 lbs in the waist pockets.
I've tried many different weight configurations so that I would have weight to ditch in the event of an emergency (in the integrated pockets), but it usually throws my trim off so that my knees drop to almost a 40 degree angle. I moved my tank up inch by inch, and now I have it adjusted just right so that I can get completely horizontal and keep my knees up. When I mention it to a new buddy before diving that I don't carry ditchable weight, I sometimes get a lecture. Other buddies (my tech/caving friends) say that I don't necessarily need to have ditchable weight if I am perfectly trim w/o it.
So, what's the verdict? Is it absolutely essential to put the weight in a ditchable location, even if it means I will no longer be trimmed out?

 

[Clammy]

Ditchable isn't suppose to be about trim, it's suppose to be about buoyancy in the event of failures. Of course you could have all the ditchable you want and in the event that say your dry suit fails, and your bladder.. and your tank is full of gas... you're not going to be buoyant anyways and your'e going to have ditch the rig or bust out the lift bag since swimming that much weight up is really hard!

By the way, what IS the proper word because apparently nothing thinks "ditchable" is a real word!

 

[ligersandtions]

If you can go down with a full tank of air/gas (the time you are heaviest), to a point where you have full compression of your wetsuit, take all of the air out of your wing, and can still swim your rig up with all the weight you normally would need to maintain your safety stop, then you don't need ditchable weight. If you find that you require more weight to keep you down than you can swim up (with no aid of your wing), then you will need ditchable weight. The amount of ditchable weight you will need depends on how much total weight you need (when properly weighted) and how much weight you can swim up with a full tank - take the difference of these two conditions and that's the amount you need to ditch in an emergency.

 

[nereas]

Drysuits are particular on sizing. I've been looking for one since August. Have not found something that would fit me. As a lady's small is still large on me. Its a work in progress if I don't want something custom or too spendy.

If you can afford the $1500 pricetag on a custom ordered trilam suit, then I would highly recommend it. Custom ordered is really nice in a drysuit. Mine is.

 

[Clammy]

If you can afford the $1500 pricetag on a custom ordered trilam suit, then I would highly recommend it. Custom ordered is really nice in a drysuit. Mine is.

I agree... but mine was just a bit more... like a lot bit more.

 

[Teamcasa]

Drysuits are particular on sizing. I've been looking for one since August. Have not found something that would fit me. As a lady's small is still large on me. Its a work in progress if I don't want something custom or too spendy.

Have a look at a White's Fusion Drysuit - plenty of threads here on ScubaBoard about them

My wife loves her Fusion. Unless you are leprechaun, the Fusion 2XS/XS will fit you.
Whites Diving | Fusion Dive Suit

 

[Charlie99]

If you can go down with a full tank of air/gas (the time you are heaviest), to a point where you have full compression of your wetsuit, take all of the air out of your wing, and can still swim your rig up with all the weight you normally would need to maintain your safety stop, then you don't need ditchable weight. If you find that you require more weight to keep you down than you can swim up (with no aid of your wing), then you will need ditchable weight.

I mostly agree with your 1st sentence, but not the second. If you can't swim a full tank back up from depth, then you have a dangerous situation. If you ditch more weight that the weight of gas currently in your tank, then you will not be able to control your ascent when shallow or do a shallow stop. (Unless you started off overweighted in which case some of the lead you are ditching you should have never been carrying anyway.)

Or to put it another way, if you are relying upon ditchable weight to get you up off of the bottom, then you should never dive to a depth & duration beyond which you are willing to do an uncontrolled ascent directly to the surface.

The only people that should be facing this sort of problem are people with very thick wetsuits, such as a full 7mm over a 7mm vest or farmer john. Of course, there are also some people that just keep piling on more and more lead and are grossly overweighted, but this problem - in theory at least - should be correctable simply by doing a proper weight check.

Even if you can swim a full tank up off the bottom, you may still want sufficient ditchable weight to give yourself good positive buoyancy on the surface in case you need to wait a long time for a boat. Usually ditchable weight equal to the weight of your air, or even a bit less, will be enough to make staying on the surface easy. IMO, this 'surface ditching' weight doesn't have to be instantly ditchable. I'm OK with this weight being on a weightbelt beneath a crotch strap or being weights that need to be removed from a pocket in order to ditch them.

Charlie Allen

 

[dumpsterDiver]

I mostly agree with your 1st sentence, but not the second. If you can't swim a full tank back up from depth, then you have a dangerous situation. If you ditch more weight that the weight of gas currently in your tank, then you will not be able to control your ascent when shallow or do a shallow stop. (Unless you started off overweighted in which case some of the lead you are ditching you should have never been carrying anyway.)

I think you exaggerate the problem of the buoyant ascent. Have you ever practiced one with full scuba gear on, when you are maybe 15 lbs buoyant? It is NOT that hard to control a buoyant ascent.

The diver who has ditched their lead should plan on doing a safety stop as a deeper depth, maybe 30-35 feet where the suit expansion has not caused a big problem. From that point up they should be able to flare out and keep the ascent rate down to a safe level. Certainly this is possible if someone were to ditch a 8-10 lbs which is more than the weight of air in a typical tank.