Best explanation on OC ratio deco I've found so far..........if this is correct, or how this can be used on CCR buggered if I know,....so I'll stick to vplanner, computer(s) & backup slate.
If your computer or depth timer goes tits up isn't this irrelevant as you don't know time & depth etc?
Thread #1
Tech1 Ratio Deco - Explained - Page 5
David.
You can simplify that even more.
Background
RD for T1 splits the ascent up into three phases:
- the 20fpm "deep stops" phase
- the gas switch at 70 feet to 20 feet
- the time spent hanging at 20 feet.
The start of the 20fpm ascents is determined by 80% of ATA and just continues up to 70 feet. For a 150 foot dive this is 110 feet. For a 170 foot dive this is 130 feet. Taking depth minus 40 feet is a way to keep it simple for tech1 dives.
The time spent going from 70->20 is set to be equal to the time spent hanging at 20 feet. Or, alternatively, half your deco time is awarded to 70->20 and half to hanging at 20. You linearize all the stops from 70->20.
The total deco time at 150 feet is equal to the bottom time (20 mins @ 150 = 20 mins deco, 30 mins @ 150 = 30 mins deco). For every 10 feet deeper/shallower you add/subtract 5 mins of deco time.
Standard Profiles
You wind up with basically three profiles, 10 minute deco, 20 minute deco and 30 minute deco:
1-1-1-1-1-5 = 10 mins
2-2-2-2-2-10 = 20 mins
3-3-3-3-3-15 = 30 mins
Examples
So for 20@150 (20 min deco):
110->70: 20fpm
70->20 : 2 min stops
20: 10 mins
For 30@150 (30 min deco):
110->70: 20fpm
70->20: 3 min stops
20: 15 mins
for 10@170 (20 min deco):
130->70: 20fpm
70->20: 2 min stops
20: 10 mins
for 20@170 (30 min deco):
130->70: 20fpm
70->20: 3 min stops
20: 15 mins
for 30@130 (20 min deco):
90->70: 20 fpm
70->20: 2 min stops
20: 10 mins
for 40@130 (30 min deco):
90->70: 20 fpm
70->20: 3 min stops
20: 15 mins
Restrictions
T1 is a single 50% deco gas class, with a max depth of 180, and max planned deco of 30 mins. The ratios only work around 10-30 minutes of bottom time and 130-170 feet, as you get outside that window they work less well.
Interpolation
And if you need 25 minute of deco, interpolate something like:
2-2-2-3-3-13
But generally with RD you're doing "too much" deep deco anyway, so I'd also be fine doing this:
2-2-2-2-2-15
Planning
This makes it generally easy to plan a dive with someone else that knows ratio deco. Generally you do it backwards and you figure your deco time to be 20 or 30 minutes (which tells you if you're doing 2s and 10 or 3s and 15). Based on your max depth you adjust your runtime to hit your deco time (if you're doing a 30 minute deco you're typically doing 20@170 or 30@150). Based on actual runtime you'll have the deco captain call a bit more or less deco.
That last paragraph there is really how you go about doing ratio deco.
Theory
A lot of it is just due to playing around with deco planners and inserting deeper stops and noticing that it doesn't change the overall deco time much, which gives the divers leeway to move stops deeper in order to simplify things. The 50/50 split from 70->20 and 20 foot stops keeps it easy, but 60/40 and 40/60 will also work. What v-planner spits out works, linearized deco works, and just about anything else reasonable that approximates a curve and gets the total time right will work. *BUT* if you play around with edge conditions and find a profile that doesn't work in v-planner, then *DON'T* do that -- *DO* play around with v-planner to find the edges.
HTH
