Future of OC trimix

[broncobowsher]

Last year off Catalina. We had a spot picked out. Boat showed up. The currents were ripping in that spot. We moved to a different wreck. It does happen. It isn't always the weather above the surface that stops you, it is the weather below the surface as well. California diving is diving on the side of a mountain that happens to be underwater. The tides are predictable, even the major currents are predictable. But the daily, and even hourly conditions are not.

The boats have room on them. But not big enough for everyone to bring there doubles, and a second set of doubles just in case they go to a shallower site.

I tend to keep 3 different blends for the rebreather. Air (or near air) for shallow stuff. Shake downs, pool, etc. A mix good for 150' and a 200' mix. Those depths are "good up to" numbers. The more important difference between the 150 and 200 mixes is the O2 levels, the 200 is lower so you can do a flush and get the PPO2 down.

 

[Celt]

We get very good 12 to 24 hour forecasts, tides are predictable with springs and neaps. If there's a front blowing through it will cancel any diving on the affected area so no real option to move to another site.

 

[formernuke]

Forecasts are very accurate, if there's a likelihood of having to move to another site then bring the bottom gas for that if on OC. No different than bringing a rebreather and bailout. Exactly what sites are you referring too. Not many 60m sites that are blown out when you get there, where you have the option to go to a 40m one

Where you are at perhaps, not around here. We have a saying if you don't like the weather wait 5 minutes it will change. I've canceled or moved dive sites from my driveway or after arriving at site one. I've also had charter captains change the site after we had already departed the dock because conditions changed.

 

[Celt]

Where you are at perhaps, not around here. We have a saying if you don't like the weather wait 5 minutes it will change. I've canceled or moved dive sites from my driveway or after arriving at site one. I've also had charter captains change the site after we had already departed the dock because conditions changed.

We get squally changeable weather ahead of a cold front but unless we got a small craft warning we wouldn't change plans.

 

[boulderjohn]

Weather issues led to my discovery of a rare and mostly unknown safety problem in scuba--Shallow Water Helium Narcosis (SWHN).

A friend and I drove for two full days from Colorado to Pensacola, Florida in a van chock full of scuba equipment in preparation for group dives on the wreck of the Oriskany. The rest of the group flew to Pensacola and met us there. When we got there, the weather in Pensacola was perfect--not a cloud in the sky and not a breath of wind. We were told, though, that the weather was too bad to dive the Oriskany. Apparently it was too windy by the wreck. (We took their word for it, but I have since come to believe that the Oriskany does not in fact exist, since I have been in the Pensacola region 11 different days over the years ready to dive, only to be told that the weather may be great there, but out by the fabled Oriskany, it is too bad. Classic bait and switch.)

So we had double danks filled with 18/45 and assorted deco bottles, and nowhere to go with them. Not wanting to waste a trip, we went to Morrison Springs and dived the cavern there, using our 18/45 doubles. That is when I discovered SWHN.

Shallow Water Helium Narcosis is a phenomenon that occurs when diving high helium trimix in shallow water. You are constantly distracted from your dive by hallucinations of dollar bills flying away.

 

[Wibble]

Forecasts are very accurate, if there's a likelihood of having to move to another site then bring the bottom gas for that if on OC. No different than bringing a rebreather and bailout. Exactly what sites are you referring too. Not many 60m sites that are blown out when you get there, where you have the option to go to a 40m one

Means bringing two twinsets, one with ~18/35 the other 28%. Both would use the same 50% and 80% deco gas.

Big challenge is being prepared with both twinsets.

 

[Celt]

Means bringing two twinsets, one with ~18/35 the other 28%. Both would use the same 50% and 80% deco gas.

Big challenge is being prepared with both twinsets.

No point if your blown off 60 m wrecks around Ireland. The only places worth going would be Lough Swilly, ( SS Laurentic among others ) or Bantry Bay French frigate La Surveillante in 35m.

 

[Tracy]

I ran into a similar situation last year on the Great Lakes. Forecast looked great for the wreck we wanted to hit at 55m, but whenever we got up there the winds had shifted and turned everything up in that area. We ended up on a wreck at 30m instead. It is not uncommon to run into this situation in the Great Lakes. I've had buddies who took gas out for a 60m dive and ended up on ones that were 25-30m instead.

Can't be true. Mac64 says it can't happen.

 

[Celt]

Can't be true. Mac64 says it can't happen.

Very intelligent, how long did it take you to think of that ? Of course it can happen but you can use air or nitrox in 40m or less not 18/50. No need for the spurious argument for rebreathers. It's only divers stuck with rebreathers that have to use them, OC divers have a lot more choices. They can dive the gas they wish to use not the one they have to. I can dive all the wrecks I wish to on air and it's free. And then there's always that one diver that looks up at the sky and says " I think the weather is going to change maybe we should cancel or move to a shallow dive,"

 

[Wibble]

Rebreathers are so much more flexible than open circuit. They're a lot safer too given the myriad options for resolving issues before resorting to a full bailout.

Memories of a dive boat doing three 60m/200ft dives on consecutive days. On a rebreather this means using two ali80 bailouts and bringing one spare diluent and oxygen (you'd get two dives out of one diluent/oxygen cylinder, maybe three). Gas and lime costs for all three dives circa $60, probably less.

Was diving open circuit then. I simply couldn't bring enough kit with me for the three days, only doing two days. I had to bring two twinsets plus five ali80s (2x50%, 2x80% and a bottom stage with backgas). I had to use two marina trolleys to move that lot and it nearly killed me pushing it up a ramp (needed to enlist the help of a bystander too). Cost me $300 for gas alone for the two dives.