Check my Logic from AL80 to PST E7-100

[dnishio]

OK, I have been looking over old threads and think I have this down right but just want to check and make sure.

I currently dive mostly with a renter Alum. Catalina S80 and am looking at buying a Steel PST E7-100, so. . .

CAT S80:
31.6 lbs (Empty)
-1.6 Buoy, Full
+4.0 Buoy, Empty

PST E7-100:
33.0 lbs (Empty)
-8.5 Buoy, Full
-1.0 Buoy, Empty

So, the buoyancy numbers take into account the weight of the tank so I would not need to be concerned with the empty weight of the tank other than hauling it around on land, correct? The real issue in terms of being able to drop lead from the belt deals with the empty buoyancy swings, so from aluminum (+4.0) to steel (-1.0), I am looking at potentially being able to drop about 5 lbs. from the belt, correct?

I understand there will be differences in weight distrubution that will effect trim but I wanted to make sure I have the whole concept of the buoynacy right first.

Thanks a bunch,

 

[D_O_H]

OK, I have been looking over old threads and think I have this down right but just want to check and make sure.

I currently dive mostly with a renter Alum. Catalina S80 and am looking at buying a Steel PST E7-100, so. . .

CAT S80:
31.6 lbs (Empty)
-1.6 Buoy, Full
+4.0 Buoy, Empty

PST E7-100:
33.0 lbs (Empty)
-8.5 Buoy, Full
-1.0 Buoy, Empty

So, the buoyancy numbers take into account the weight of the tank so I would not need to be concerned with the empty weight of the tank other than hauling it around on land, correct? The real issue in terms of being able to drop lead from the belt deals with the empty buoyancy swings, so from aluminum (+4.0) to steel (-1.0), I am looking at potentially being able to drop about 5 lbs. from the belt, correct?

I understand there will be differences in weight distrubution that will effect trim but I wanted to make sure I have the whole concept of the buoynacy right first.

Thanks a bunch,

Looks right to me. I recently switched to an E7 100 from AL80s and dropped 6 lbs from the trim pouches on my Ranger.

The weight of the tank on land is irrelevant for buoyancy purposes, but is nice to consider when thinking about how much you're lugging around on the surface (especially for shore dives). The net loss of a few pounds on land was surprisingly noticeable for me.

 

[Dryglove]

The real issue in terms of being able to drop lead from the belt deals with the empty buoyancy swings, so from aluminum (+4.0) to steel (-1.0), I am looking at potentially being able to drop about 5 lbs. from the belt, correct?

Yep, you could remove 5lbs from your weight belt by going from the alm80(+4lbs) to the E7-100(-1lbs)

 

[jonnythan]

Your terminology is off. The swing on the Al80 is 5.6 pounds, and for the E7 is 7.5 pounds. The swing weight is the weight of the gas inside, so obiously 100cf weighs more than 77.4

What's important for your weighting is the empty buoyancy, which you figured out allows you to drop 5 pounds of lead. This ensures that you will retain the same buoyancy at the end of the dive.

Start at 5 and do a weight check at the end of the dive though.

 

[dnishio]

Thanks for the confirmation and additional information.

 

[wmspdi]

I use a simple rule... If I dive with my E7 100s I don't use any weights in the trim pouches of my back inflate BCD. If I am using a rental AL 80 I use 2- 3lbs weights in the back trim pockets (one on either side). Since I use a back inflate BC the heavier weight of the steel tank tends to keep me upright at the surface. The Al80 tends to push me on my face without the trim weights.

You could also make up a little tank weight belt from an old BC cam band. Place a 3 lbs weight on either side of the tank between the BC tank strap and the boot (adjust the position on the tank for trim). This will keep a near empty tank from trying to float away from your back and you won't have to change your weight belt when you switch from steel to aluminum tanks.

 

[c555]

When I went to steel 100's from rental 80's, I dropped 4 pounds. Now i carry less total weight than w/ and 80 and weight, which is a real help in a drysuit.

 

[spectrum]

Ooops