Help deciding on HP Tank Size

[diverrobs]

I am new to diving and have all my gear except tanks. I am seriously considering spending the $800 or so on two HP tanks but am having a hard time deciding what to buy. I did a little figuring on my spread sheet and have figured the following out given that I am diving with my dry suit and need 18lbs with an Al80 tank.

Tank Weights Tank Weight Total Weight Pre Dive Post Dive
Al80 18 31.4 49.4 -6 Neutral
HP80 11 28 39 -6 Neutral
HP100 11 33 44 -7.5 Neutral
HP120 12 38 50 -9 Neutral

Basically if my math is correct and I looked the data up correctly on the internet, the total dry land weight with the HP120 is pretty much the same as with the Al80, but I sink really fast and have 1.5 times the bottom time. With and HP80 I have a dry land wieght of 10lbs less than with an AL80 but no other advantage. With an HP100 I weigh about 5lbs less on dry land than with an Al80 and will have 25% more bottom time.

So if I have to interpret this data, I would say that the HP120 is the best bet becuase I will be the same wieght on dry land, and have more bottom time.


Am I right, the HP120 looks like the best tank for the $ given it is only $100.00 more than the HP80 and $40 more than the HP100. Disregarding $ is there any real advantage to HP80 or HP100 that I have missed.

Thanks in advance.

 

[spectrum]

There is no arguing that CF per dollar the HP 120 is the best HP buy.

Extra air is great as long as your buddy has comparable runtime. I use the term runtime because the reality of it is a combination of available gas and consumption rate.

Diving a bigger cylinder will by definition consume a little more air so to a slight extent it is self defeating.

If weight on your feet such as for shore dives with signifigant entry and exit walks is a concern you can't beat the HP80.

This may be helpful

Pete

 

[dannobee]

The HP120's are tall, and may hit your butt when swimming. Try to borrow one before you buy to make sure it "fits."

 

[The Kraken]

The HP 119's are nice, short and hold lots of gas, but they're 8" diameter tanks.

The HP 100's are really sweet.

the K

 

[Lightning Fish]

I would have to suggest a HP130. It is a beautiful tank. When I started looking at tanks I was considering the 120. When I saw how long it was, and that extra bit of air, I went with the 130.

Cheers,
Bill.

 

[The Kraken]

Good suggestion, L/F . . .

The HP 130's are also 8" diameter tanks. They are very close in size to the HP 119's but just a little bit heavier.

But there is the matter of an extra 10 cubic feet of gas.

the K

 

[diverrobs]

I think the HP100 is the way to go. My dive buddy probably won't have the steel tanks and will be stuck with Al80 rentals. So with the HP100 I get the extra air, same physical size as the Al80 and less total weight. Seems like a win, win, win for me. The 130s would have so much air that I would be wanting more bottom time when my buddy is ready to go up.

Also because most of the wreck diving here in Ontario is pretty deep >60' I suspect my bottom time will be more limited by N2 absorption than by air consumption. On an 80cf tank I have been able to get 50 min. at 50' and at 100' I had 900psi after 20min. (no-decompression limit) at 100'. As such my guess is the 100cf meets my needs best.

Thanks for the help, I really hadn't considered the extra length and the fact that my buddy probably will limit my time once I have a larger volume tank.

 

[Jimmer]

HP100's are quite popular for wreck diving around here, I see a lot of them find their way onto our dive boat. If you want to try before you dive, the shop that I deal with, has both HP80, and HP100's in rental. We run charters in Lake Erie around the Long Point area.

 

[texdiveguy]

I might look at a HP130....nice for single tank diving.