Interesting Experience on Spiegel Grove

[WreckWriter]

Did a fairly aggressive penetration dive on the SG Saturday night. Very good dive, max depth 122, BT 60 minutes. My buddy and I went through a large percentage of the wreck, only popping outside for brief periods. Other than the dive being overall interesting I learned something about computer usage as it applies to this site.

As you may know the SG lies on her side in about 130 fsw. The beam is so wide that the side of the hull lies in only an average of about 50 fsw.

Diving with my VR3 set for EANx 32, everything was going fine until about 2/3 of the way through the dive I looked at the computer and it said "use tables". Hmmmmmm......

It kept track of the remainder of the dive but continued to show the "use tables" message.

Yes, I did my deco on tables.

Following the dive the VR3 showed a "missed deco" message. Hmmmmmm ..... I did all the deco that it asked for and quite a bit more. Why would it say I missed deco?

It took me a while to figure it out but I now think I know what happened. It's somewhat disconcerting and is a possible problem on this particular wreck when doing an aggressive dive on ANY computer.

With the 85' depth variation it's possible to enter the wreck at 120' or deeper and exit at about 50'. What I believe happened to me is that I had built up enough deco to have a stop at below 50' and that the computer thought I was starting deco when in reality I was still diving happily along. I'm guessing that this happened at a point where we had exited the well deck and swam around the lower hull to the props. We then came up and over the hull so would have been at around 50' for up to a minute or a bit more.

An even more disconcerting possibility is that I actually passed through a deco stop inside the wreck. Possible.

Something to keep in mind on this wreck. Never dive (here or anywhere) without your tables!

Tom

 

[TexasMike]

Some good points about any type of wreck diving.

Glad to here you're okay. And I guess I'll get the chance to shake your hand next week (Pete still hasn't told me which day yet)

 

[WreckWriter]

Originally posted by TexasMike
Some good points about any type of wreck diving.

Glad to here you're okay. And I guess I'll get the chance to shake your hand next week (Pete still hasn't told me which day yet)

This is the only wreck I know of that can generate this sort of profile, most have nowhere near this amount of relief.

As for next week, likely not, no time to plan and most busy at work (wish it were otherwise).

Tom

 

[MikeFerrara]

That kind of profile could easily happen in a cave. You need to be prepared for the need to deco up to a shallower section not only at the end of the dive. The VR3 is RGBM, correct? That means your stops will start deeper than with a haldanian model.

How do you likke the VR3 in general?

 

[WreckWriter]

Originally posted by MikeFerrara
How do you like the VR3 in general?

All in all I find it a useful tool. It's real good for moderate dives but if you give it a good push it will give a deep bubble stop which makes it tough to stay with others who are diving tables. A safer profile than the table profile without the deep stop in my opinion. I think if one's buddy was also diving a VR3 it would be great.

It's a good unit, I'm happy with it.

Tom

 

[Scuba446]

I would like to learn about deco diving more...not that i am ready to venture into that yet - still a fairly green OW diver, but I use a Bottom Timer and would like to know how to handle a dive if we ever mess up and go 'over' the NDL.

How can I learn enough to protect ourselves and insure our safety?

??

 

[Tegg]

Originally posted by Scuba446
I would like to learn about deco diving more...not that i am ready to venture into that yet - still a fairly green OW diver, but I use a Bottom Timer and would like to know how to handle a dive if we ever mess up and go 'over' the NDL.

How can I learn enough to protect ourselves and insure our safety?

??

As a responsible and trained diver you should easily not go 'over' your NDL limits. It is similar to gas management, you should keep an eye on your air supply, so why not your depth and time?

If you seriously want to know what to do after the NDL limit, get decompression training from a good instructor.

Dive Safe.

 

[Fetch]

As an aside (and quite related), I heard a net.rumour of someone getting bent on the SG (and with the depth variance, I could indeed see that happening).

Has anyone else heard this or have more information?

Tom - good to hear you had no problem making the deco, sounds like an interesting dive

jeff

Originally posted by WreckWriter

With the 85' depth variation it's possible to enter the wreck at 120' or deeper and exit at about 50'. What I believe happened to me is that I had built up enough deco to have a stop at below 50' and that the computer thought I was starting deco when in reality I was still diving happily along. I'm guessing that this happened at a point where we had exited the well deck and swam around the lower hull to the props. We then came up and over the hull so would have been at around 50' for up to a minute or a bit more.

An even more disconcerting possibility is that I actually passed through a deco stop inside the wreck. Possible.

Something to keep in mind on this wreck. Never dive (here or anywhere) without your tables!

Tom

 

[BradfordNC]

not familiar with the workings of your dive computer, but here is a possibility.

can you change the sampling rate of the computer?

if so, and it is set for a longer sampling rate, like every 60 seconds, then it is possible that diving a profile similiar to the one you did in the SG that you could have had a depth change between samples that triggered the error, even though you were safely within limits.

for someone used to diving relatively flat profiles, the high rate won't make much difference. but i can see where the various increases and decreases in depth from moving through a wreck with as much relief as the SG would call for a tighter sampling rate.

just a thought

 

[WreckWriter]

BradfordNC once bubbled...
not familiar with the workings of your dive computer, but here is a possibility.

can you change the sampling rate of the computer?

if so, and it is set for a longer sampling rate, like every 60 seconds, then it is possible that diving a profile similiar to the one you did in the SG that you could have had a depth change between samples that triggered the error, even though you were safely within limits.

for someone used to diving relatively flat profiles, the high rate won't make much difference. but i can see where the various increases and decreases in depth from moving through a wreck with as much relief as the SG would call for a tighter sampling rate.

just a thought

That makes a lot of sense Brad. I don't think it can be changed but I'll look into it. Thanks.

Tom