How much lift?

[E_Mo]

I am taking a search and recovery class, which requires a 50 pound lift bag. I have an approximate 6'x6" SMB with dump valve which I think would work in lieu of a true lift bag, does anyone know how much lift this size of a SMB would have?

[Nwbrewer]

About 30 lbs if my math is right.

[CaptnJack]

I am taking a search and recovery class, which requires a 50 pound lift bag. I have an approximate 6'x6" SMB with dump valve which I think would work in lieu of a true lift bag, does anyone know how much lift this size of a SMB would have?

6" diameter = radius of 3"
a cross sectional area of 0.25 x 0.25 x 3.14 = 0.196ft2 x 6ft = 1.17 cf
1 cf of water weighs about 62cf so 1.17 x 62 = 73lbs displaced.

Given some taper at the top and bottom you are probably looking on order of 60-65lbs of lift. Precise diameter will make a huge difference in actual lift capacity. Have you checked the manufacturer's website for lift info?

Any instructor demanding you actually retrieve a 50lb object in class is being a bit pendantic IMHO.

[E_Mo]

I checked the manufacturer's (oxycheq) website, but there wasn't any information;
http://oxycheq.com/index.php?main_page= ... cts_id=285

This is the SMB I have;
http://www.scubatoys.com/store/detail.a ... MarkerBuoy

I don't know what size of objects we are working with, but maybe 50 pounds is just the recommended size (is also the smallest one they sell).

[CaptnJack]

Who's your instructor? You should talk with them anyway as a SMB is not really a lift bag although it can do in a pinch.

[Nwbrewer]

I am taking a search and recovery class, which requires a 50 pound lift bag. I have an approximate 6'x6" SMB with dump valve which I think would work in lieu of a true lift bag, does anyone know how much lift this size of a SMB would have?

6" diameter = radius of 3"
a cross sectional area of 0.25 x 0.25 x 3.14 = 0.196ft2 x 6ft = 1.17 cf
1 cf of water weighs about 62cf so 1.17 x 62 = 73lbs displaced.

Given some taper at the top and bottom you are probably looking on order of 60-65lbs of lift. Precise diameter will make a huge difference in actual lift capacity. Have you checked the manufacturer's website for lift info?

Any instructor demanding you actually retrieve a 50lb object in class is being a bit pendantic IMHO.

I thought 6" was the measure across the face when flat? (uninfltaed)
So circumference = 12 in => 12/(2*3.14) = radius of ~2in
a cross sectional area of 0.17 x 0.17 x 3.14 = 0.0908ft2 x 6ft = .544 cf
62*.544= 33lbs of lift?

It gets worse when you look at his link. It's 6' long, only 5 gets filled with air. The last foot or so is the duck bill, so it may be as little as ~30lbs.

I agree with Richard on lifting something 50lbs with a bag for training. That's a pretty heavy object to go for at first. I recovered a 12lb anchor the first time, and even that was a little interesting to keep neutral on the ascent.

[coulterboy]

I am taking a search and recovery class, which requires a 50 pound lift bag. I have an approximate 6'x6" SMB with dump valve which I think would work in lieu of a true lift bag, does anyone know how much lift this size of a SMB would have?

6" diameter = radius of 3"
a cross sectional area of 0.25 x 0.25 x 3.14 = 0.196ft2 x 6ft = 1.17 cf
1 cf of water weighs about 62cf so 1.17 x 62 = 73lbs displaced.

Given some taper at the top and bottom you are probably looking on order of 60-65lbs of lift. Precise diameter will make a huge difference in actual lift capacity. Have you checked the manufacturer's website for lift info?

Any instructor demanding you actually retrieve a 50lb object in class is being a bit pendantic IMHO.

I thought 6" was the measure across the face when flat? (uninfltaed)
So circumference = 12 in => 12/(2*3.14) = radius of ~2in
a cross sectional area of 0.17 x 0.17 x 3.14 = 0.0908ft2 x 6ft = .544 cf
62*.544= 33lbs of lift?

It gets worse when you look at his link. It's 6' long, only 5 gets filled with air. The last foot or so is the duck bill, so it may be as little as ~30lbs.

I agree with Richard on lifting something 50lbs with a bag for training. That's a pretty heavy object to go for at first. I recovered a 12lb anchor the first time, and even that was a little interesting to keep neutral on the ascent.

Damn you engineers. That's why I didn't follow my dad's footstep being an engineer (mechanical and electrical). I hate numbers.

[CaptnJack]

I am taking a search and recovery class, which requires a 50 pound lift bag. I have an approximate 6'x6" SMB with dump valve which I think would work in lieu of a true lift bag, does anyone know how much lift this size of a SMB would have?

6" diameter = radius of 3"
a cross sectional area of 0.25 x 0.25 x 3.14 = 0.196ft2 x 6ft = 1.17 cf
1 cf of water weighs about 62cf so 1.17 x 62 = 73lbs displaced.

Given some taper at the top and bottom you are probably looking on order of 60-65lbs of lift. Precise diameter will make a huge difference in actual lift capacity. Have you checked the manufacturer's website for lift info?

Any instructor demanding you actually retrieve a 50lb object in class is being a bit pendantic IMHO.

I thought 6" was the measure across the face when flat? (uninfltaed)
So circumference = 12 in => 12/(2*3.14) = radius of ~2in
a cross sectional area of 0.17 x 0.17 x 3.14 = 0.0908ft2 x 6ft = .544 cf
62*.544= 33lbs of lift?

It gets worse when you look at his link. It's 6' long, only 5 gets filled with air. The last foot or so is the duck bill, so it may be as little as ~30lbs.

I agree with Richard on lifting something 50lbs with a bag for training. That's a pretty heavy object to go for at first. I recovered a 12lb anchor the first time, and even that was a little interesting to keep neutral on the ascent.

I have no idea. Every lift bag I've ever heard of has an advertised lift! 50lb ones are pretty inexpensive through Piranha ~$40 or so.

[renoun]

I think the main problem with using a big SMB as a lift bag is that the OPV is in the wrong place to facilitate making a controlled ascent. A proper lift bag will have an OPV on the top allowing air to be vented even if it isn't full while a SMB usually has the OPV at the bottom where it will only vent if the SMB is full.

[Nwbrewer]

I think the main problem with using a big SMB as a lift bag is that the OPV is in the wrong place to facilitate making a controlled ascent. A proper lift bag will have an OPV on the top allowing air to be vented even if it isn't full while a SMB usually has the OPV at the bottom where it will only vent if the SMB is full.

Another excellent point.

[CaptnJack]

What is this "neutral ascent" with a lift bag business?!? Just send the damn object up to be recovered by the boat crew!

[Nwbrewer]

What is this "neutral ascent" with a lift bag business?!? Just send the damn object up to be recovered by the boat crew!

I always thought having the heavy thing headed to the surface above my head was bad form....

Or is it launch bag, hit trigger, hope for the best?

[CaptnJack]

What is this "neutral ascent" with a lift bag business?!? Just send the damn object up to be recovered by the boat crew!

I always thought having the heavy thing headed to the surface above my head was bad form....

Or is it launch bag, hit trigger, hope for the best?

You think anyone messes trying to keep their prizes neutral for an hour or more while they finish their deco? Just use a closed bag and send 'er up.

That said, you can get an object just barely negative and then with a slight pull from the surface bring it all they way up relying on gas expansion once you've gotten it moving. Some people do this with their anchors when boat diving, makes pulling it up sans windlass a snap.

[Nwbrewer]

What is this "neutral ascent" with a lift bag business?!? Just send the damn object up to be recovered by the boat crew!

I always thought having the heavy thing headed to the surface above my head was bad form....

Or is it launch bag, hit trigger, hope for the best?

You think anyone messes trying to keep their prizes neutral for an hour or more while they finish their deco? Just use a closed bag and send 'er up.

That said, you can get an object just barely negative and then with a slight pull from the surface bring it all they way up relying on gas expansion once you've gotten it moving. Some people do this with their anchors when boat diving, makes pulling it up sans windlass a snap.

Yeah, I did the anchor trick on the PP Ferry once, much better than dragging it up by hand.

[kdupreez]

I live in Snoqualmie Ridge and have 50lb and 100lb bags, open and closed..

If you need to borrow one, I'll meet you in issaquah and you can use it for class..

pm me if you need one..

Koos

[E_Mo]

Thanks for all of the info. With all said, I went ahead and bought a lift bag (before I saw kdupreez's offer.... but thanks anyways).