Question What mix to use for 200ft (60m)

[Dann-Oh]

Hey there. First off this post is not intended to be a short cut around training but rather I'm trying to decide if I should look into rebreather or stay open circuit. I am pointing out I have not takes any "tec training" yet. I'm planning to take TDI sidemount and start AN/DP by the end of this year or early next year depending on finances. I am planning to do as much of my diving in sidemount as possible so (4 cylinders or less).

My ultimate goal is to get over to the Great Lakes and dive the shipwrecks in Lake Huron, Michigan, USA, it seems that a lot of the wrecks are at about the 200ft (60m) mark. So my question is what mix of trimix would I be using for these dives? I have a young family so I can see myself being able to get away for 1 week (7days) a year for this kind of trip. a 7 day trip likely means 5 days of diving, I hear the common rule of thumb is "2 deco dives a day keeps the doctors away" I'm not too sure if 200ft(60m) is considered a big deco dive, if it is then it would be "1 deco dive a day keeps the doctors away".

So If I'm doing 5-10 dives a year to 200ft does a rebreather make sense? Would anyone be willing to help me out with what I would be expecting to carry when it comes to back gas and deco gas?

 

[sea_ledford]

The availability of helium OC trimix will probably make the decision for you. You can look up one of the many best mix gas planners, or a table of GUE standard gasses to see what your mix would likely be (probably 18/45 off the top of my head), but you may not even be able to purchase fills for OC diving, regardless of how much you are willing to spend.

Pre-no-more-helium-for-OC days, I considered 200 feet my cut off for OC anyway. The tank logistics alone just seemed to be more than I was willing to deal with, and that would only be for an occasional 200' dive. 150-170 or so is where I would max out OC deco diving. If 200 is the regular target, CCR is the way to go. But you'll have to dive way more than 1 week a year to remain proficient. If you aren't even deco certified yet, at one week a year, your kids will be in college before you are doing 200' CCR dives.

 

[tursiops]

So my question is what mix of trimix would I be using for these dives?

Normoxic Trimix is fine....the basic TDI Trimix course, not advanced.

So If I'm doing 5-10 dives a year to 200ft does a rebreather make sense?

No, except maybe financially, given the cost of Helium. At 5-10 rebreather dives year, each time you use it will be like starting over.

 

[divingx]

So my question is what mix of trimix would I be using for these dives?

21/35 to 45 metres/150 feet and 18/45 to 60 metres/200 feet if you plan to use standard mixes.

I'm not too sure if 200ft(60m) is considered a big deco dive, if it is then it would be "1 deco dive a day keeps the doctors away".

I prefer one longer dive over two shorter dive to 200ft range. Getting in and out of water with all the gears, especially with heavy undergarment in summer on the Great Lakes, is PITA.

So If I'm doing 5-10 dives a year to 200ft does a rebreather make sense?

IMO the only logical way to keep diving Trimix is to get a rebreather. To fill a set of double HP100 with 18/45 here would cost you CAD $337/USD $250. 10 Trimix dives a year will cost you maybe USD $2000 given that you should have some Trimix left from the previous dive. Also, Helium is not available in many areas. Sometimes you need to bring all the gas you need, or at least all the Trimix you need. With rebreather it’s a lot easier.

 

[Dann-Oh]

The availability of helium OC trimix will probably make the decision for you. You can look up one of the many best mix gas planners, or a table of GUE standard gasses to see what your mix would likely be (probably 18/45 off the top of my head), but you may not even be able to purchase fills for OC diving, regardless of how much you are willing to spend.

Pre-no-more-helium-for-OC days, I considered 200 feet my cut off for OC anyway. The tank logistics alone just seemed to be more than I was willing to deal with, and that would only be for an occasional 200' dive. 150-170 or so is where I would max out OC deco diving. If 200 is the regular target, CCR is the way to go. But you'll have to dive way more than 1 week a year to remain proficient. If you aren't even deco certified yet, at one week a year, your kids will be in college before you are doing 200' CCR dives.

To be clear I'm getting a diving day about every other week to every 3rd week, my kid is 2 years old now so I'm sure as he gets older I'll be able to get more days of diving as he gets older. I'm getting a few dives in during my diving day. I'm in southern California so I have lots of diving to get practice but my 1 week diving vacation to Lake Huron is an honest reality guess.

If I were to get into a CCR, I would be using it on a lot of local dives, top places like wreck alley in San Diego and various other places around Catalina.

Normoxic Trimix is fine....the basic TDI Trimix course, not advanced.

okay cool. I do not have any desire at the moment to get deeper than 200ft. But I also once said the same thing about tec in general.

No, except maybe financially, given the cost of Helium. At 5-10 rebreather dives year, each time you use it will be like starting over.

If I were to get into a CCR, I would be using it on a lot of local dives, top places like wreck alley in San Diego and various other places around Catalina. I would not always be using it with trimix though.

21/35 to 45 metres/150 feet and 18/45 to 60 mitres/200 feet if you plan to use standard mixes.


I prefer one longer dive over two shorter dive to 200ft range. Getting in and out of water with all the gears, especially with heavy undergarment in summer on the Great Lakes, is PITA.

That makes total sense. Im just at the idea generation phase and trying to plan my spending properly.

IMO the only logical way to keep diving Trimix is to get a rebreather. To fill a set of double HP100 with 18/45 here would cost you CAD $337/USD $250. 10 Trimix dives a year will cost you maybe USD $2000 given that you should have some Trimix left from the previous dive. Also, Helium is not available in many areas. Sometimes you need to bring all the gas you need, or at least all the Trimix you need. With rebreather it’s a lot easier.

If I were to get into a CCR, I would be using it on a lot of local dives, top places like wreck alley in San Diego and various other places around Catalina. I would not always be using it with trimix though.

 

[broncobowsher]

Another beni of the rebreather is if plans change. You were planning on that 200' dive, the boat shows up, looks at conditions, leaves. Got this other spot over here that is protected but only 140'. Now you have a choice. Burn that expensive fill in a set of doubles, pass on the dive.
Just last week I was doing 80' dives on a 200' mix on the rebreather. Second dive of the day, first was deep. Doing 3-4 dives on a single fill of a little 3L bottle. Yes, I was wasting some of my expensive deep mix, but so little of it I didn't care.

 

[rx7diver]

... Pre-no-more-helium-for-OC days, I considered 200 feet my cut off for OC anyway. ...

My very first 200 ffw dive was on the SS Daniel Morrell in Lake Huron, east of Port Sanilac MI, ca. 1995. I'll have to find my old logbook to say if it was a training dive for my IANTD Advanced Deep Air certification, or my first "real" dive after I received that cert. So long ago.

Air (manifolded HP100's) as a bottom gas for sure, and one deco cylinder (OMS/Faber LP45) carried for sure, but I can't recall now if it contained EAN36 and we did overboard oxygen, or if it contained oxygen.

We had "trained up" for these dives, but I couldn't remember jack from the dive! How many propellers? Number of blades on the propeller(s)? I got nothin'!

ETA: I do remember that we wanted to get as deep as possible. There was a hard bottom at 200 fsw. We were wearing Cochran computers (wrist receiving unit, and sending unit mounted on the first stage). We buried our wrists in the silt to get as much depth as possible. (See the problem?)

rx7diver

 

[PfcAJ]

you really need to think about how proficient you are going to be with that kind of schedule.

You won’t be building up any experience on OC, and if the rebreather breaks, you’re an Oc diver at 200’. So you think you’re going to be skilled enough to be in that position having only a small handful of dives?

Beware.

 

[Tracy]

Financially at 5-10 dives per year, the math won't ever work out. Helium is currently still too cheap for that.
Logistically, good luck with OC trimix.
I know of three Great Lakes operators that still fill OC trimix, myself included.
As helium costs continue to rise, the OC divers get less and less. The infrastructure to support OC trimix is substantial, it is worthwhile and profitable when you have 6 divers buying it everyday. When you have a boat with 4-5 rebreathers and one guy diving OC, you lose money trying to support them and it isn't worth the headache.

So unfortunately, even though it doesn't make financial sense yet, it will probably be the only option within the next five years.

 

[Dann-Oh]

you really need to think about how proficient you are going to be with that kind of schedule.

You won’t be building up any experience on OC, and if the rebreather breaks, you’re an Oc diver at 200’. So you think you’re going to be skilled enough to be in that position having only a small handful of dives?

Beware.

So what kind of schedule are you going to recommend? As I mentioned in other comment/responses, I plan to dive locally (southern California) to build up experience (and time on a rebreather if I get into one) but my big goal is to get to Lake Huron to see the ship wrecks.

Financially at 5-10 dives per year, the math won't ever work out. Helium is currently still too cheap for that.
Logistically, good luck with OC trimix.

So it sounds like youre saying the cost of rebreather for 5-10 dives a a destination is too expensive but filling OC bottles is getting harder to do? I plan to dive locally (southern California) to build up experience (and time on a rebreather if I get into one) but my big goal is to get to Lake Huron to see the ship wrecks.

I know of three Great Lakes operators that still fill OC trimix, myself included.

I checked out your site, I'm quite interested in reaching out to you when I am able to visit.

As helium costs continue to rise, the OC divers get less and less. The infrastructure to support OC trimix is substantial, it is worthwhile and profitable when you have 6 divers buying it everyday. When you have a boat with 4-5 rebreathers and one guy diving OC, you lose money trying to support them and it isn't worth the headache.

So unfortunately, even though it doesn't make financial sense yet, it will probably be the only option within the next five years.

So it sounds like getting into a rebreather sooner than later is the way to go? I can see myself doing a bunch of OC decompression diving without trimix here locally in Southern California.