Newbie questions for the BP/Wings crowd

[mattengstrom]

I'm a new diver - been certified for a little over a month and have a whopping 11 dives to my name so far. So, this may seem painfully obvious to some of you, but I've been reading a LOT on this board and can't quite figure this out.

First - I'm a fairly dense guy. (No, not THAT way!! I mean in the body.) On my recent vacation - trip report here - I was using a rented ScubaPro Glide Plus BC. Depending on what I was wearing, I either had 6 or 8 pounds on my weight belt in the tropical salt water.

From what I've been able to figure out, a stainless steel backplate has about 6 pounds of negative bouyancy. Right?

Here's what I can't figure out: If I had been wearing a stainless BP/Wings setup, those 6 pounds plus any trim weights make up all of the weight that I need. I would have had little to no ditchable weight. Well, I could have carried an additional 10 pounds but then I would have been way over-weighted and still just about neutral if I dumped all of it. From what I was taught and what I've read - like this - that idea scares the crap out of me. I should be able to ditch some or all of my weight and get positive.

Am I missing something here, or are stainless BPs out of the question for me if I want to be able to dump weight? If that's the case, can I use an aluminum BP in salt water? Just how bad is the corrosion aspect?

Just trying to piece things together before I go out and buy equipment...

 

[Dryglove]

mattengstrom once bubbled...

If that's the case, can I use an aluminum BP in salt water? Just how bad is the corrosion aspect?

Bingo!! Sounds like your the perfect candidate for an AL bp. Talk to fredt or pm him from here on the board about his aluminum bp's. He makes a high quality product. I own one of his SS heavy BP's.

 

[Wendy]

I have had no corrosion on my Al bp diving it in salt water. Just like any of your gear, you should rinse your gear with fresh water after diving in the salty stuff.

 

[ElectricZombie]

If you want ditchable weight, you might want to look into the AL BP. As long as the rig is balanced (meaning you are able to swim it up from depth with total wing failure) ditchable weight is not required. However, if having ditchable weight makes you more comfortable, go for it.

 

[filtered]

Aluminum plates don't really corrode. However they do oxidise, making the appearance err....not so nice. One way to get round this is probably to powder coat the backplate.

Also if using aluminum plates, u may want to get some nylon washers to put beneath the wing nuts, to prevent electron transfer as the nuts are stainless steel.

 

[MikeFerrara]

mattengstrom,

The people in the Rodales stories seem to have a lot of issues besides the need for ditchable weight. As always they skip lots of things to get to the point their trying to make.

If you are near neutral (only neg by the weight of the air in your tank) why and how much ditchable weight would you need? To much ditchable weight, IMO, is as bad or worse than none. On the surface you could alwyas sip out of the rig if you were unable to inflate. It,s true that you shouldn't be so heavy that you can't get to the surface but that doesn't mean getting 20 pounds pos either.

Something to think about...

I have seen many rapid ascents. Some of them resulted in injury. OTOH, I have never seen a situation where some one needed to drop weight at depth or was injured because they couldn't. Ever see some one loose a weight belt or an integrated pouch? I've seen it many times not to mention the number of weight belts and loaded integrated pouches I have found on the bottom without a diver attatched.

I wouldn't suggest putting to much stock in anything Rodales says.

 

[FredT]

filtered once bubbled...
Aluminum plates don't really corrode. However they do oxidise, making the appearance err....not so nice. One way to get round this is probably to powder coat the backplate.

Also if using aluminum plates, u may want to get some nylon washers to put beneath the wing nuts, to prevent electron transfer as the nuts are stainless steel.

Painting or powder coating equipment that lives in sea water is usually counter-productive. An uncoated Al or Stainless plate, hardware or tank will take a patina and then effectivly stop corroding except where some electrochemical force is driving it. Where the coating is damaged and base metal is exposed any electrochemical attack will be concentrated at the cating holiday. I've seem pressure vessels fail in single digit days due to a coating failure where driven with much less than a volt. Current density makes all the difference in corrosion rates, so try to have the sacrificial anode side very large compared to the cathode. This is why Aluminum is often bolted with stainlees. The Al cotrrodes and is driven by the protected fasteners, but the fasteners are generally the highest stressed part and can't deal with the corrosion if aluminum frsteners were driven by a much larger strainless space frame.

The washers are a good idea, but sue a harder plastic like PVC, Delrin or Torlon. Nylon Cold flows too much to be an effective long term solution