When do you Consider Surface Assistant.

[Wookie]

I do that dive 5 times a year, by the way. Probably in warmer water.

 

[Remy B.]

I wouldn't "require" surface support for that dive and certainly not any support divers. Surface support is always nice to have so you take it when you can get it, and the boat crew counts as that.

For that dive, I wouldn't personally use a 21/25 bottle or any deep trimix bottle. I would either swap it and the 50/50 bottle for a 30/30 bottle, or stay on backgas until I got to the 50/50 bottle. If you stay on the deep mix, it only increases your consumption to ~250cf/7000l for easy math, which isn't all that much. That is a pair of LP95's for those of us in the states.
Doing that dive, you plan with the boat crew that you'll shoot a DSMB when you get to the deep deco mix to signal you are OK or if you need help. If you need help, that's obviously preplanned for how the boat is going to react to that kind of situation if your buddy is unable to help you resolve.

I would need at least double that decompression before I planned for a support diver.

the 21/25 is a travel gas to get you out of the water quicker, and is the worse case scenario backup for BTG @ 1.67PPO, if you stay on back gas your Deco tanks grow. the 30/30 you mention is as well an option for travel gas but not for worse case scenario backup with 2.35PPO at 70m

 

[Wookie]

There is being conservative with a travel gas, then there is being task loaded with 6 cylinders. If I planned a dive that required 6 cylinders, I'd go buy a rebreather. Diving 6 cylinders, while doable, is an invitation for disaster. Not to mention all you'll do is stress your back.

Have you made a dive with 6 cylinders before?

 

[LiteHedded]

I'd do that dive with 50% and o2

You shouldn't need any support for such a short exposure

 

[Diver0001]

I'm curios if the Wreck professionals consider a Surface Assistant or they relay completely on them self in the most demanding dives. it is well understands that you need to be self sufficient and carry all your gear with you, but for big dives ( OC ) I guess ( and maybe wrong ) you can carry so much bottles to a point to be unpractical and I believe dangerous to some point.

Of course it is of each individual risk assessment under which risk they determine their dives and are willing to go for that deep and long dive.

What I mean with a Surface Assistant or how I pictured ( never met one nor I know the complete spectrum of their duties ), is a Diver that stays in surface monitors the dive time and have waiting for you at 9m or 6m that extra backup O2 Deco bottle, in that will meet you at the 21m stop to see if everything is alright or assist you if needed, and/or wait for that SMB to come up with a note saying you have problems below, and he will dive down with that extra gas/gear you need to safely return to surface.

I don't know if you are asking about local diving or not but for practical reasons it's hard to imagine a wreck dive here that would be longer than about 1-1/2 hours using open circuit. The reasons have to do with the water temperature and the tides, particularly on the North Sea, but also with the available air supply. Obviously if you dive on the North Sea you will be doing it from a boat so surface support is part of the deal.

On wrecks we swim to from shore (there are a few) the dives are seldom longer than about 70 min in the summer. In particular the "lood & touw" wrecks make for an interesting dive but the way we do it gas supply and depth usually means that the most you get is about 20-30 min of deco with air. It would be a LOT more than that if you swam the distance back over the bottom, which is why some local divers say these wrecks can only be explored with scooters, but we do the swim back mid-water. It takes 20-25 min to get back to shore and we do the stops while swimming. Normally the stops are almost done by the time we encounter the bottom again during the swim back. For that particular dive having any kind of surface support or staging deco bottles somewhere is pointless because navigation can be tricky and nobody on the surface would know where you are.

In any case, regardless of the wreck I would find it highly ill advised to stage *necessary* deco gas anywhere other than carrying it with you. There is always a chance that you will have to make a free ascent and given the visibility we have, no non-trivial wreck around here can be dived without a risk of not finding the up-line again.

R..

 

[tbone1004]

the 21/25 is a travel gas to get you out of the water quicker, and is the worse case scenario backup for BTG @ 1.67PPO, if you stay on back gas your Deco tanks grow. the 30/30 you mention is as well an option for travel gas but not for worse case scenario backup with 2.35PPO at 70m

I know what a travel gas is and on why you would want to be on a high PO2 earlier, but why do you need a third gas at the bottom? You better be doing that dive on doubles or sidemount which gives you the normal redundancy. I don't see the need to carry an extra bottle just so you can have a third gas on the bottom.

 

[Remy B.]

There is being conservative with a travel gas, then there is being task loaded with 6 cylinders. If I planned a dive that required 6 cylinders, I'd go buy a rebreather. Diving 6 cylinders, while doable, is an invitation for disaster. Not to mention all you'll do is stress your back.

Have you made a dive with 6 cylinders before?

4 only at the moment ( with two small Deco tanks ), I'm not there yet to do 6 tanks, that I consider the max to carry

 

[Remy B.]

I don't know if you are asking about local diving or not but for practical reasons it's hard to imagine a wreck dive here that would be longer than about 1-1/2 hours using open circuit. The reasons have to do with the water temperature and the tides, particularly on the North Sea, but also with the available air supply. Obviously if you dive on the North Sea you will be doing it from a boat so surface support is part of the deal.

On wrecks we swim to from shore (there are a few) the dives are seldom longer than about 70 min in the summer. In particular the "lood & touw" wrecks make for an interesting dive but the way we do it gas supply and depth usually means that the most you get is about 20-30 min of deco with air. It would be a LOT more than that if you swam the distance back over the bottom, which is why some local divers say these wrecks can only be explored with scooters, but we do the swim back mid-water. It takes 20-25 min to get back to shore and we do the stops while swimming. Normally the stops are almost done by the time we encounter the bottom again during the swim back. For that particular dive having any kind of surface support or staging deco bottles somewhere is pointless because navigation can be tricky and nobody on the surface would know where you are.

In any case, regardless of the wreck I would find it highly ill advised to stage *necessary* deco gas anywhere other than carrying it with you. There is always a chance that you will have to make a free ascent and given the visibility we have, no non-trivial wreck around here can be dived without a risk of not finding the up-line again.

R..

Just a general question not related to Dutch waters in particular.

 

[Remy B.]

I know what a travel gas is and on why you would want to be on a high PO2 earlier, but why do you need a third gas at the bottom? You better be doing that dive on doubles or sidemount which gives you the normal redundancy. I don't see the need to carry an extra bottle just so you can have a third gas on the bottom.

It is just my perspective how I will do a dive like that, for the reasons I mention.

 

[PfcAJ]

I wouldn't sign up to be reliant on support on any dive, and certainly not on an ocean dive.

The plan being discussed is relatively simple and only requires two deco gases. The 3rd bottle just adds complexity with very little benefit on such a short bottom time.

Keep it simple.