opinions for size of tank for recreational sidemount diving in coldwater

[westcoastross]

Hi Everyone, i am new to the site and haven't been able to see any older posts addressing this situation.

as a cold water BM drysuit diver, i carried a HP100 and slung an al40 as a redundant air supply. after 45min to 60 min dives at max depth 100'+ i would regularly surface after safety stops with 1000+ psi or 34 cubic feet of air still in my steel.

now i have switched to sidemount (SMS75) and am not sure what tanks i should be using for recreational diving. i've been playing with 2 x al40's, 2 x lp45's ...(ya i know..funny) but there is not enough air for redundancy. 2 x hp100's are over kill for recreational diving, and al80's are just too light to be used with my cold water gear.

unfortunately there are no dive shops around here that rent or have different size tanks to try aside from al80's.

using the rule of thirds, i figure i need 165ft3 of air for 2 x dives + an additional buffer for extra air. it seems that my options are something like HP80's, or lp85's. i haven't dove with either of these tanks and dont have the ability ot see what they would be like in the water without ordering them in from my lds.

anyone else in the same situation that has found a solution?

Thanks

 

[00wabbit]

LP85s are the same size as hp100s fyi.

I had lp85s and for 2 tank dives off a boat it wasn't quite enough for me so I went to hp100s.

A lot of people will say get lp85s then you can get them overfilled if you need more gas. I tried that route but because I travel a lot with them I haven't been able to get overfills reliably. That's the main reason I switched to the 100s.

 

[Jim Lapenta]

HP 80's, at least the ones from PST are very short and depending on your build may be very hard to trim. I was diving LP85's yesterday in the local mudhole. now all of this was shallow stuff with an Intro to Tech student working on skills but I got three 45 min dives and came home with 1000 PSI in each tank. Of your choices I would recommend the LP 85's. Easy to trim out, lots of gas, and if you can get overfills of 3000 PSI you've got 95's. With HP 80's you have to hope that you get good fills of 3445 and some shops don't seem to know how to do that or won't. They give you a hot fill of 3500 that cools to 3300 giving you 76's or worse they give you a 3000 PSI fill and you end up with 69 cu ft per tank. If I had a limited budget based on my use of the LP85's and the LP 75.5's I have I'd look for a used set of LP 72 steels if I could not get the 85's. How hard is it to get fills for you between dives? If it's tough I'd also consider setting up two sets of LP 72's. You can likely pick up four of them for just over the cost of one new LP 85. I've seen them go around here for 50 - 75 bucks each.

 

[a878bob]

What's the problem with AL80's ? I dive them with my cold water rig all the time. Plenty of air down to 200'. Easy to move around and carry, easy to trim.

 

[westcoastross]

Thanks for your help.

my lds will not fill the older 72's... they are real sticklers. not a bad thing.. they said they would fill them if they were in mint condition, but due to their age, they wouldn't for many more years to come. all fills here are hot fills unless you only want to dilute the nitrox mix with air if you are in a hurry.

i use my 2 x HP100's for deeper dives or when training for tec, but i don't want to hall these around for a 80' wall dive. and i don't wish to carry 4 tanks with me on a boat. i did this with my al40's and lp45's. they were ok due to their small size, but it is too much gear.

seem like steel 80's or 85's are my best option. just wish i could try them out first.

---------- Post added August 31st, 2014 at 01:51 PM ----------

the main problem i've experienced with al80's using a drysuit in coldwater is the extra weight needed to be neutral. at 6' 210lbs i need 33lbs of lead with al80's compared to 22lbs with steels. thats a big difference. especially as im using a SMS75.

 

[a878bob]

I'm also 6', 210, and carry about 24-26lbs in my rig, with heavy undies. I rig to be neutral without any cylinders as I will normally clip everything off to a line when doing deco. And climb out with no cylinders. It seems the problem is not the weight itself but how to hang it on the rig. I had the same problem. The solution for me was to add a Xdeep double central weight pouch to my backstrap. It fits between the plates easily, can be adjusted, secure closure. It is really a nice solution. I also have 2 xsscuba weight pouches on the waist. Easy to add any amount of lead. The problem I find with my hp100's is being too light without them both on. Might as well be diving BM at that point.

 

[Dhboner]

I use HP 100's with my drysuit and 200 gram undies slung on my SMS 75 with no additional weight. They trim out nice and their weight isn't a problem (I am 56 years young).

 

[rjack321]

Too bad your LDS won't fill lp72s, not only are they a good size they are cheap too. I just bought 5 for $25 although they need hydros. Your LDS completely missed the mark on why its actually wise of them to not fill 72s... Not because of their age, USDOT 3AA spec tanks can and do last 75+yrs. I have some in my stable from before WW2. No the actual reason should have been because lp72s were never TC approved so they aren't legal to fill in Canada.

Sadly that doesn't leave you many options. Lp45s are dreamy tanks to dive but small for your profiles. Steel lp50s, if overfilled to 3000+, would be ideal though.

 

[ffdiver]

Lp 50s are awesome tanks to sidemount. But even topped off to 3600psi they won't give you the gas you are calculating. What I do if I wanna do two longer dives with them is use them on the first and then carry an 80 stage on the second.

 

[mk706]

I sidemount HP100s for recreation and tech diving. I find the 100s are way too small for back mount tech diving.

Diving the SMS75 wet with the 100s is no problem at all.

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