Weighting going from warm to cold salt water

[topher10]

I normally dive the florida panhandle in relatively warm water (above 70 degrees). I have a DSS stainless steel backplate with LCD20 wing. My standard setup is my 3mm full wetsuit with no additional weight. If the water gets into the mid 70s I wear a 3/5 hooded vest under the wetsuit, and add 4 pounds. I love this setup. I was recently in a spring with 68 degrees and I got cold by the 3rd dive of the day, but it was April and raining, so I never warmed up between dives.

Due to work travel I will increasingly have the opportunity to dive in SoCal. I just passed up a trip in early May, but have another chance in November and will definitely go next March to Ventura. I predict the water will be in the 50s when I go in March, and so I am trying to make plans for gear and the funding of any necessary purchases. My plan is to rent at 8mm suit with hood and also gloves from the dive shop, and therefore I will unable to precisely measure my bouyancy change until I get there.

So here are my questions:
1. Any rough guestimates on the added weight necessary in going from 3m full to 8m plus hood and gloves.
2. Should I swap to a steel tank to reduce required weight on my weight belt. I can look up weights for various steel tanks relative to Al80. Would like to try an HP100 if I have a chance.
3. Should I be concerned with only a 20lb wing.

I like that with my warm water setup I have no problem swimming up a full tank (Al80) with no air in the wing. I don't want to be so heavy that 20lb of lift is not enough. I dont think this will happen but thought I would ask. Ideally I also don't want to be so heavy that I cant swim up if the wing fails, thus the question about tank weight vs. weight on a belt.

Thanks as always.

 

[tbone1004]

In an 8mm suit with a HP steel tank, you might not need any lead. If you do, 4lbs should be more than enough. I would highly recommend going steel if you can.

I would be concerned with a 20lb wing...

 

[topher10]

That is my fear. I do not want to buy a bigger wing just for these rare cold water trips. So perhaps I should just rent a BC when I get there.

 

[shurite7]

Using a an HP ST100 in cold water is really nice.

The general rule of thumb when it comes to lift is to have ten more pounds of lift than what you wear. If you are using twenty pounds then a thirty pound lift BCD is recommended.

Divers, up here in MT, who use a semi-dry 6.5mm suit with a ST72 tank generally use between twenty and thirty pounds of lead.

 

[outofofficebrb]

Based on my experience with my 3mm and what I am in my semi-dry 8/7...If you are diving AL80s, maybe about 4 pounds difference if you are going from a 3mm to an 8mm. If you are diving HP100s, you might not need any weight. I say definitely go for an HP100 or steel tank if you can, especially if you are beach diving....A few extra pounds saved is less you have to haul up and down!

I'm still trying to figure my weighting out since I just started diving with HP100s and a relatively newer SolAfx 8/7 semi-dry with 5mm boots and 6/4 gloves. I'm somewhere in the range of 135 pounds right now and have started with 12 pounds. The first couple of feet are tougher to descend on so I have to duck dive but after, it's fine. I haven't gotten to the low tank pressure to be able to find out if I'm truly neutral at a safety stop with an empty wing yet.

 

[cmrangel]

Some fairly quick rule of thumb numbers:
1. About 3 lbs/mm of wetsuit - can be slightly more for a floaty, soft wetsuit. This is for a size L or XL. Can go as low as 2.5 lbs/mm for small.
2. For cold water, add 3 lbs for hood, gloves, boots. Can be a pound or so plus or minus
3. Buoyancy difference between HP100 and AL80 is about 4.5 to 5 lbs (depends on the HP100 exact tank) at 500psi

So, to go from 3mm w/AL80 and no hood, gloves to a So Cal 8mm with Hood, Gloves, and HP100
Weight difference = 3 lbs/mm*(8mm-3mm) + 3 lbs - 5 lbs = 13 lbs more lead needed on belt or integrated.

This is just a starting point, some wetsuits are more/less floaty, etc

I would say the 20 lbs would not be enough. Even if you use a weight belt and are not concerned about floating the rig with weights attached (as in an integrated system), compensation for the buoyancy changes alone (Wetsuit compression and tank air loss) would be close to or more than 20 lbs. The buoyancy of the wetsuit is (roughly) 3lbs/mm * 8 mm = 24 lbs + 3 lbs (Hood, gloves, etc) = 27 lbs. At depth, you can lose 2/3 or so of this so the change would be 27 * 2/3 = 18 lbs. Plus you will lose 5lbs or so of gas with a HP100 for a total loss of up to 23 lbs. Again, this is just a very rough calculation to get a basic idea and can vary a lot based on wetsuit, etc. For some safety margin, I would look at something in the 30 lbs range

BTW. I dive So Cal and most folks use a 7mm but you specifically mentioned a 8mm. If you use a 7mm, you can save a few pounds.

 

[topher10]

Looking at the various rental shops, it seems like it would actually be a 7mm wetsuit, and thus 20lbs of lift might be enough but it will be cutting it close. For what its worth, the first few trips will likely be one of the various boats out of Ventura or Santa Barbara to the Northern Channel Islands, or on a separate trip diving out of San Diego (not sure boat or beach or both). For instance, work meeting starts on Monday, so I fly in Friday and dive and sleep on the boat over the weekend before meetings/conference.

So my choices are:
a) Take the risk with my current wing. I would need to wear the minimum weight necessary to get underwater, and then be prepared to be heavy at depth at the start of the dive until I breath down the tank. Not sure if Al80 vs steel 85 or 100 makes a difference beyond moving weight to/from weight belt.
b) Buy 30lb wing.
c) Just rent a BCD at the same time I rent the wetsuit and tank.

I am probably going to go with the last option, just for simplicity and easy of travel if nothing else. BCD rental adds ~$35/trip.

Thanks for the thoughtful advice.

 

[cmrangel]

Yes, I would not take the risk, these are not 100% accurate calculation and I never trust the lift numbers published. Especially if it is in a new environment for you. Plenty of places to rent a BCD. If you need advice on shops, etc. you can post in the So Cal forum or if it is in San Diego area, you can PM too.

One thing about the HP100 vs Al80, because the have different buoyancy characteristics, you do end up slightly less dry weight with a HP100 (around 3 or 4 lbs if I recall). You can drop about 5 lbs off the weight belt because of the buoyancy but the dry tank weight is only 2 lbs more. Also, with the HP100 the weight is distributed on your back. Of course, the biggest difference is in the air capacity and if you want the extra bottom time.

 

[drbill]

I can only offer guidelines based on my personal diving. In tropical waters I wear a 3/2mm full wetsuit and dive with 20# on my belt and a 20# wing whereas here at home in cold water I dive a 5mm or 7mm full wetsuit and hooded vest with 32-38# on my weight belt and a 32# wing.

Our general rule of thumb out here is 10% of your body weight plus 5-7# for weights

 

[stuartv]

That is my fear. I do not want to buy a bigger wing just for these rare cold water trips. So perhaps I should just rent a BC when I get there.

You don't know anyone that can loan you a bigger wing for an occasional trip?

There is lots of time if you wanted to monitor the SB Classifieds and eBay to pick up a bigger wing for cheap.