Dive plan question

[flw]

There are a couple of wrecks in the Mackinac Straits that I would like dive on again. The difference is, this time I would like the dives to be in the one hour range or maybe slightly longer. The depths are 110 to 120+. How would you manage this kind of dive?

Personally dependant on the wreck I'd use a ccr with 10/50 as a diluent and carry a 7l of 50%. 30 minutes bottom time will bring me out under the hour - but if it was interesting enough I'd stay longer. I carry tables up to 45 minutes for all depths in my pocket, so if it got beyond 'g-plan' I could default to pre-run tables.
Alternatively twins with 30% possibly with an 80% for deco to get out quicker, possibly on their own.
Much would depend on whether or not I was planning on penetrating to any distance or simply swimming round.
In the UK it would be considered a completely normal recreational dive and no-one would think anything of it.

 

[limeyx]

Why Not?

V Planner gives it less deco than 100 feet for 20 minutes on air which is recreational.

(The 120 for 20 was on 30%)

I was commenting on the 35 mins safety stop part

 

[limeyx]

LOL, hey that was yet another angle I didn't see.

...
If you want 60mins of BT, spread it out over two dives and have far less overhead to worry about.

Hmmm, if only I'd said that in post #3 ...

 

[ianr33]

I was commenting on the 35 mins safety stop part

You are confusing me.

If I do a 35 minute safety stop at 15 feet. (Or just hang out at that depth looking at pretty fishes )that makes it a technical dive?

Technical Diving:
1)Any dive below 130 feet
2)Any dive involving deco
3)Any dive involving an overhead
4)Any dive with a safety stop longer than 5 minutes ??????!!!!

 

[Atticus]

To make this play by PADI's rules you should consider it a multi-level dive, with the second segment at 15' (calculated at 35').

If I recall correctly PADI defines the end of bottom time as the time when a direct ascent to the surface with an optional 3 minute safety stop at 15' begins.

This is of course a silly diversion and in no way intended to answer the original posters question. I'm only quoting PADI's RDP to be cute - this is obviously either a shorter no stop "recreational" dive or a longer technical dive. The only way the above answer is relevent is if the diver really wants to spend an hour in the water doing a no stop dive and doesn't mind spending most of it shallow.

To answer the OP's second question about what sort of training to pursue -- take a look at http://www.naui.com/technical_divers.php.

 

[Doc Intrepid]

FWIW, IMHO the most important bit of input so far has been Scuba Steve in post #18. If you look at the profile that Atticus provided in post #15 you'll see 55 minutes of bottom time with some 29 minutes (variable to surface) of required deco. Thats a total runtime of nearly an hour and a half in the water.

The wrecks in the Straits of Mackinaw have lots of sharp edges. The water is real cold and, on most days, pretty dark at 110'. If you have no issues at all, you can get pretty chilled in that water for an hour and a half. But if you DO have issues, such as a puncture in your drysuit, and you have a half hour of mandatory decompression to finish, you can become hypothermic before you can get out of the water.

Plus, the weather can change rapidly in the Straits...during the 90 minutes you're submerged it can go from nice to snotty pretty fast.

It would be a whole lot safer to plan two dives with shorter exposures - say under an hour total runtime, each - than to deliberately plan one long 55 minute BT/90 minute runtime dive given those environmental parameters.

JMHO. YMMV.

Doc

 

[ianr33]

Hi Merlin

Agree that this is totally a silly diversion !!

I may be spending a few weeks in Tahoe later in the year,will drop you a line when I know more. Suspect I will enjoy Tahoe diving more now that I have a drysuit

 

[Atticus]

It would be a whole lot safer to plan two dives with shorter exposures - say under an hour total runtime, each - than to deliberately plan one long 55 minute BT/90 minute runtime dive given those environmental parameters.

Point taken. As I don't dive those waters I don't know the local conditions. If I get a chance to (dive there) I'll take your advice.

I may be spending a few weeks in Tahoe later in the year,will drop you a line when I know more. Suspect I will enjoy Tahoe diving more now that I have a drysuit.

I'd be delighted dive with you again. I picked up a little (18') boat for getting to the harder to reach dive spots.

 

[grazie42]

Late to the thread but...
I´d do 35mins @ 120ft
bring ean80 for a total divetime of 59mins
If that´s too much hastle, skip it, spend 77mins in the water instead...

For a real dive I´d modify this a bit (from the v-planner table I took this from) but how I´d do that would depend on circumstances...If I had some ean50 lying around, I´d use that for a RT of ~65mins...I´ve done that kind of dive in 40ish water and a flooded DS with nothing more than the discomfort of being cold and wet as a result...

Maybe that´s too much effort, not suitable for the site or something but that´s the way I´d do it (with the 80)...

like the other replies have shown...there are plenty of ways to go about it, imo, the way you do it is mostly down to personal preference...

 

[limeyx]

You are confusing me.

If I do a 35 minute safety stop at 15 feet. (Or just hang out at that depth looking at pretty fishes )that makes it a technical dive?

Technical Diving:
1)Any dive below 130 feet
2)Any dive involving deco
3)Any dive involving an overhead
4)Any dive with a safety stop longer than 5 minutes ??????!!!!

I kind of misread the post. A 35 min "saftety" stop is misleading. it would really either be

1) a deco stop and non recreational
2) part of the dive (and if within the NDL then rec if not then not)