Wing Lift - Cold water, 8/7 semi-dry suit

[mtoyama]

Also, I forgot to say -- I often bring a large-ish camera rig with me, but I don't think it matters for this as I use floats and weights to make it roughly neutrally buoyant.

 

[inquis]

If I play with some of the variables it can go down to 26-36, or up to 30-40+, etc.

Do yourself a favor and measure the buoyancy of your suit near the surface. That will greatly narrow the uncertainty about required lift. You will also have a more realistic idea about the required swim up if the wing fails.

Put the suit in a mesh bag with enough lead to just sink it in a pool, hot tub, trash can, or similar. If you have a luggage scale, it's fine to be a few pounds heavy. Just measure without the suit as well and take the difference.

 

[inquis]

Putting 6 lbs on the backplate waist belt makes it easy to drop that at the beginning of the dive when you still have all your air in that HP100. (You'll breath 6.5 to 7 lbs off during a dive to reserve pressure.) That might get you "over the hump" on the initial swim up, and you'd preserve your normal end-of-dive neutral depth (normal ascent from that point).

 

[Brett Hatch]

Yes! My last 6 dives have been out there! I love it. Honestly it's what's motivating me to buy my gear: I learned I want to do dives with a mission, and what better mission than conservation work?

Are you trained up?

Yes I am. Have not managed to get a dive in since the course though (for urchins or otherwise). I tried a week or two ago to do it off of my kayaks, but ran into some problems and had to abort. It's fun work, I'm glad to hear you are sticking with it. Maybe we'll bump into each other out there some time.

This I wasn't thinking about. Honestly, I've never really had a not-cold dive in California waters, wearing all kinds of rental suits. I might just be susceptible to cold.

Maybe, it does seem to vary a lot, person to person and day to day. I know that I'm a lot more sensitive to it than some of my other dive buddies. Dry suits do cost a bit more, but it ain't an arm and a leg, I'm happy with it. But maybe you'll find a way to make the semi-dry work, a lot of people out here dive wet all the time. One of the local instructors here never wears gloves and I've seen him without a hood a few times, either he's nuts, or I'm a wimp... probably both.

 

[mtoyama]

By the way, if you really want to be sure it will be enough, you might want to test your wetsuit to see just how buoyant it is. Stuff the suit into a mesh bag with, say, 10 lbs of lead. Keep adding little bits of lead until the suit begins to sink. Add up the weight of all the lead, and that's the amount of lift your wing needs to provide to compensate for suit compression. Add to that the amount of gas you're diving (100 cubic feet of air weighs 8 pounds), and you will find the absolute minimum amount of lift you need to bring along. Maybe throw in a couple extra pounds for a margin of error.

OK I did this just now, and my suit began sinking at 25lbs in the pool. I think it's somewhere between 23 and 25 as it sank hard.

I updated my buoyancy spreadsheet with this number, also adding in estimated buoyancy for 5mm boots and 3mm gloves and it now has my wing lift range from 25-30 lbs: link to spreadsheet. Note I entered my max depth as 100'.

If I had added the tank weight to this it would be well over 30 lbs.

Why is the buoyancy calculator number so much lower? Now I'm confused.

 

[mtoyama]

I studied the spreadsheet more, and I think the assumption here is that at 100' you still retain a bit of wetsuit buoyancy, thus 30lbs being fine if I'm not overweighted.

 

[inquis]

the assumption here is that at 100' you still retain a bit of wetsuit buoyancy

Yes, this is shown in cell F11 of the Lift sheet. Almost 7 lbs of wetsuit buoyancy remaining.

BTW, I would measure your hood & boots as well. (You can lump them in the wetsuit bundle if you want.) My Waterproof H1 5/7 mm hood is +0.2 lbs and Cressi 3mm boots are +0.5 lbs, measured with a luggage scale, which is quite different from your 4.7 lbs currently shown. When I just looked, the spreadsheet also shows nearly 28 lbs for the wetsuit, which you know is no more than 25 lbs.

 

[mtoyama]

Yes, this is shown in cell F11 of the Lift sheet. Almost 7 lbs of wetsuit buoyancy remaining.

BTW, I would measure your hood & boots as well. (You can lump them in the wetsuit bundle if you want.) My Waterproof H1 5/7 mm hood is +0.2 lbs and Cressi 3mm boots are +0.5 lbs, measured with a luggage scale. When I just looked, the spreadsheet also shows nearly 28 lbs for the wetsuit, which you know is no more than 25 lbs.

I added the estimated buoyancy of 5mm boots and 3mm gloves from the sheet to the manual wetsuit buoyancy figure. I can measure them today too to make it more accurate.

The hood is integrated in the suit so is part of the 25lbs measurement.

 

[inquis]

Cell D24 is an override of the bottom line buoyancy you want to use. There is about 0.5 lb difference between fresh and salt for your suit, but at this point you're within measurement errors.

 

[mtoyama]

BTW, I would measure your hood & boots as well. (You can lump them in the wetsuit bundle if you want.) My Waterproof H1 5/7 mm hood is +0.2 lbs and Cressi 3mm boots are +0.5 lbs, measured with a luggage scale, which is quite different from your 4.7 lbs currently shown. When I just looked, the spreadsheet also shows nearly 28 lbs for the wetsuit, which you know is no more than 25 lbs.

Oh, sorry I misunderstood your comment initially. You're suggesting that the estimates could be off by quite a bit and I should measure them to be sure.

How does the luggage scale work? Do you add weight until it's negative in the water, then attach the bag to a luggage weight and subtract that from the total weight added?