When to use limited stash of Trimix on a boat trip? Early or later?

[walkonmars]

Hi Folks,

I hope this is the correct section to post.

For sake of argument...
If you are on a two day diving trip on a boat, you will do 3-4 dives per day (8 total).
You are allowed to take three tanks (2 HP100's filled with trimix 28/25/47, one filled with EAN XX), and one 40cu ft stage bottle with 50% O2.
The boat only fills air or EAN 32.
Let us also assume the interesting stuff to look at is in the 70ft to 120ft depth (uncertain on every dive location) and your choice when to dive there.
When will you best utilize your trimix based on this situation?

My untrained guess is use it on the second dive each day assuming you use the first dive of the day to go your "second deepest" dive of the day.
I would use the first dive (second deepest) to look around and find out if I want to go deeper.
The second day, I would repeat the plan as I did the first day.

Thanks for any comments.

-T

 

[Dr. Lecter]

Hi Folks,

I hope this is the correct section to post.

For sake of argument...
If you are on a two day diving trip on a boat, you will do 3-4 dives per day (8 total).
You are allowed to take three tanks (2 HP100's filled with trimix 28/25/47, one filled with EAN XX), and one 40cu ft stage bottle with 50% O2.
The boat only fills air or EAN 32.
Let us also assume the interesting stuff to look at is in the 70ft to 120ft depth (uncertain on every dive location) and your choice when to dive there.
When will you best utilize your trimix based on this situation?

My untrained guess is use it on the second dive each day assuming you use the first dive of the day to go your "second deepest" dive of the day.
I would use the first dive (second deepest) to look around and find out if I want to go deeper.
The second day, I would repeat the plan as I did the first day.

Thanks for any comments.

-T

Nothing in 70'-120' merits helium, so I take the 28/25 home and use it to make a useful blend like 10/50. I likely take three tanks of EAN whatever I like, though if the bottom I'll hit is 120' I'm just going to use the boat's 32% and not worry about the minor excursion above 1.4. If I want to go to 130' or there's no hard bottom in play, air (or bring three tanks of slighTROX) it is.

If I'm bringing only one 40 of deco gas, and the boat already has 32%, that 40 is filled with 100%. Topping with 32% will allow me to have something in the 100-80% range for clean-up for quite some time given the shallow depths...though if they're not PP blending their 32%, both the bottle and the reg will probably need an O2 cleaning afterwards.

 

[walkonmars]

I forgot to mention I'm diving only singles with the option to carry a pony.
Also, I'm using the "slightrox" as you refer to it to decrease some of the narcosis I'm starting to be aware of in the 100ft range. I'm doing the correct things but memories get vague and dexterity is diminished (as I see it). The boat is full and no special mixing for anyone. Air, nitrox (32) or free dive.
I mix my gas for a lot less than a shop charges so I'm just asking if you get it for low cost, how would you folks consider using it as a recreational gas?
Not much literature about helium as a recreational gas. It seems just technical or nothing when it comes to literature. Liability seems to be a big consideration when recommending helium so it seems it is only allowed for the technical guys after extensive training or nothing. Any more thoughts?

Hi Folks,

I hope this is the correct section to post.

For sake of argument...
If you are on a two day diving trip on a boat, you will do 3-4 dives per day (8 total).
You are allowed to take three tanks (2 HP100's filled with trimix 28/25/47, one filled with EAN XX), and one 40cu ft stage bottle with 50% O2.
The boat only fills air or EAN 32.
Let us also assume the interesting stuff to look at is in the 70ft to 120ft depth (uncertain on every dive location) and your choice when to dive there.
When will you best utilize your trimix based on this situation?

My untrained guess is use it on the second dive each day assuming you use the first dive of the day to go your "second deepest" dive of the day.
I would use the first dive (second deepest) to look around and find out if I want to go deeper.
The second day, I would repeat the plan as I did the first day.

Thanks for any comments.

-T

 

[Dr. Lecter]

I'm using the "slightrox" as you refer to it to decrease some of the narcosis I'm starting to be aware of in the 100ft range.

If it works for you, great, but the scientific literature I've read on the subject suggests that oxygen is at least as narcotic as nitrogen and possibly a great deal more so. I've never noticed a narcosis difference between air and nitrox, though I tend not to find much in the way of narcosis until I get outside rec depths and at that point I'm on air anyway.

You would probably have better luck posting in the advanced or DIR section, because GUE is the main group I'm aware of with a pro-rec depths helium stance. If you wanted to reduce narcosis though I guess I'd just use the trimix for the deepest dives and then top those tanks with air for following deeper dives in an effort to retain at least some He in the blend.

Regarding liability and safety of helium, while you will find plenty of people who still advocate extremely deep stops and high surfacing gradient factors with trimix, you will also find people teaching lying to computers about the helium percent in the mix and running things like 85/85 with rich trimix. About the only thing I think is consistently advocated is being able to hold a solid, neutrally-buoyant stop with helium because of its faster on/off gassing. It looks like a lot of traditional thinking about helium and diving is...maybe not wrong, but definitely not as absolute as previously thought. But make no mistake about it, it does present a greater risk of DCS and a greater risk of the nasty Type II neurological hits. You pays your money, and you takes your chances.

 

[johnkendall]

Hi Folks,

I hope this is the correct section to post.

For sake of argument...
If you are on a two day diving trip on a boat, you will do 3-4 dives per day (8 total).
You are allowed to take three tanks (2 HP100's filled with trimix 28/25/47, one filled with EAN XX), and one 40cu ft stage bottle with 50% O2.
The boat only fills air or EAN 32.
Let us also assume the interesting stuff to look at is in the 70ft to 120ft depth (uncertain on every dive location) and your choice when to dive there.
When will you best utilize your trimix based on this situation?

My untrained guess is use it on the second dive each day assuming you use the first dive of the day to go your "second deepest" dive of the day.
I would use the first dive (second deepest) to look around and find out if I want to go deeper.
The second day, I would repeat the plan as I did the first day.

Thanks for any comments.

-T

Why not just take 2 of the tanks full of Helium, and use it to blend on the boat?

HTH
John

 

[walkonmars]

Thanks guys,

Yes, I posted a question about trimix use a year ago and there was some debate about oxygen being narcotic, also.
It seems the literature I saw ("Recreational Trimix Diving") oxygen still has a significant narcotic effect (although slightly less than nitrogen). Bottom line is I need to drop the overall nitrogen and oxygen content but oxygen having slightly less narcotic effect than nitrogen is cheaper to use in order to displace the nitrogen. I agree that 28/25/47 is a wimpy mix but may buy me some marginal decreased narcotic effect.
I have been careful and attempted to model dives using Suunto's DM software but I'm too novice to model anything beyond a single dive. The repetitive dive model alludes me. I also run a Macintosh to shareware modeling software is limited.

Why I'm not taking helium tanks on board?
1.) As a courtesy and less hassle I limit the cylinders to take to 2-3.
2.) I don't have a booster to get the most out of my two helium tank bank. If I fill a small cylinder with helium to higher pressure I have dropped my ability to top off trimix mixing capability of my bank(can't top off the final pressure needed for a specified mix). I could still use the remnant helium in the travel tanks but these are Al80- tanks and I hate to dive them. I only own two HP100's.

I think I'll re-post on the Advanced forum as suggested.
Thanks for the inputs.

-T

 

[rx7diver]

Thanks for any comments.

walkonmars,

Can you use the following approach that some of my friends used to use with doubles? Fill one of your HP 100's with an immediately usable tri-mix blend. Fill your second HP 100 with a high-helium-content tri-mix blend (that is NOT to be dived as is). Then:

1. Dive the first tank.
2. Upon return, drain the first tank completely.
3. Equalize the (empty) first tank with the (high-helium-content) second tank.
4. Top up both tanks with the boat's EAN (or the boat's air).
5. Dive one of the two tanks.
6. Dive the other tank.

So, you're able to get three single tank tri-mix dives from your two HP 100's.

I can figure out the "best" choices for immediately usable tri-mix and high-helium-content tri-mix if you need me to, but you can probably just as easily do this, yourself.

If you're able to follow each tri-mix dive with a shallower repetitive dive, you can top off each HP 100 with EAN/air after each tri-mix dive. So, you'll be able to squeeze in six tri-mix dives--using your two HP 100's. Two dives per day over three days out of only two HP 100's!

Will this work for you?

Safe Diving,

rx7diver

 

[ajduplessis]

I would not use trimix on dives to 120ft, but rather Nitrox. Ean32 at 120ft is approaching PPO2 of 1.5, i would bleed of some nitrox and topup with air to get to nitrox30 (po2 1.4) for the 120ft dives. EAD for 120ft using nitrox 30 is 95ft.My concern is around trimix. The questions asked indicate a limited knowledge. I did not check, do you have any form of trimix certification? If you do, rx7 post above around mixing is good. Do you or the boat have a tx analyzer? Will the boat allow you to blend tx?

Do you have any deco cert.? If so I would rather take additional O2 to washout nitrogen in the shallows. Track your OTU over the trip and have fun.

 

[Searcaigh]

Save your helium, I would not use it for anything less than 40M (131 ft).

 

[Patoux01]

If I'm bringing only one 40 of deco gas, and the boat already has 32%, that 40 is filled with 100%. Topping with 32% will allow me to have something in the 100-80% range for clean-up for quite some time given the shallow depths...though if they're not PP blending their 32%, both the bottle and the reg will probably need an O2 cleaning afterwards.

If you're gonna clean, it means your tank has been contaminated, how do you want 80% to get contaminated? I wouldn't play with that kind of stuff, pushing non clean gas on top of pure O2...