Lift Capacity Question: HOG 4.5ft SMB

[g1138]

Anyone know the lift capacity and dimensions of a HOG 4.5ft SMB?
I can't get any info on the web.
I have a 6 footer that's 40lbs and I'd like to get a smaller smb that's has less lift capacity, preferably around 25lbs.

The basis for this is so I can have a SMB that's easier to deploy at depth and also to be used as point of reference (w/ a finger spool and line) when I'm ascending in open water with Basic OW students.


HOG 4.5ft SMB

Thanks in advance!

 

[Tortuga68]

I'm going to guess about 30#

You could try asking the question in the Edge Gear - ScubaBoard forum

BTW if anyone from Edge is reading this, the text in the link the OP provided says 6 foot not 4.5 foot

 

[g1138]

Thanks Tortuga
I forgot they had a forum.

 

[Kilili]

You can calculate the volume, Pi * radius squared * height, then convert to weight for equivalent volume of water. 1 cu in of fresh water at 62° F. equals .03608 pounds. For salt water, multiply by 1.028.

 

[g1138]

You can calculate the volume, Pi * radius squared * height, then convert to weight for equivalent volume of water. 1 cu in of fresh water at 62° F. equals .03608 pounds. For salt water, multiply by 1.028.

Nevermind, didn't check my units.
[-]I don't think that works.
I get 1.21lbs of lift capacity for a 6ft (72"X6") SMB that's supposed to be 40lbs.
And even then I think saltwater is 64lbs/cu ft., freshwater is 62.4lbs/cu ft
Air's 0.08lbs/cu ft.[/-]
I've tried to make sense of calculating lift capacity, but I can't seem to figure it out.

Plus I don't even have the dimensions of the HOG SMB, so in this specific case I'm out of luck. =[

 

[Tortuga68]

You're one step away. The lift is the difference between the weight of the air in the SMB (what you calculated) and the weight of the water displaced by the SMB:

72" * 6" SMB (3" radius)
Volume = Pi * radius^2 * H
V = 3.142 * 3^2 * 72
V = 2036 cu in

Weight of fresh water = 0.03608# per cu in
Weight of sea water = weigh of fresh water * 1.028
WOSW = 0.03608 * 1.028 = 0.03709#
Weight of air = 0.0807# per cu FOOT

Weight of sea water displaced by SMB = 2036 * 0.03709= 75.5#
Weight of air in SMB = 2036/144 * 0.0807 = bugger all (1.14 actually)

Lift of submerged fully inflated SMB in sea water = 75.5 - 1.14 = ~74# minus the weight of the deflated SMB

Or something like that

 

[g1138]

Thanks Tortuga, and you too Kilili for your help.
That's the number I've been getting, 74lbs roughly.
I just didn't believe it because the website I bought it from claimed it was "roughly 40lbs"
I did another calculation with a 4ft smb (7" X48") ~25lbs lift capacity
and got 72lbs of lift.
It just seems too high.

Go figure.

 

[SeaCobra]

Or, hang it upside down from a fish weighing scale or similar, fill it with water. Read scale, there's your lift capacity. Has the side benefit of checking for leaks.

Jeff

 

[g1138]

Thanks Tortuga, and you too Kilili for your help.
That's the number I've been getting, 74lbs roughly.
I just didn't believe it because the website I bought it from claimed it was "roughly 40lbs"
I did another calculation with a 4ft smb (7" X48") ~25lbs lift capacity
and got 72lbs of lift, I think.
It just seems little high.

Go figure.

 

[Tortuga68]

Yup, that would work too

I did another calculation with a 4ft smb (7" X48") ~25lbs lift capacity and got 72lbs of lift. It just seems too high.

Well not to be nitpicky, but that is too high... should be about 67#

But yeah, not even close to the quoted rating