Deco in caves is different from open water. For example you do a wreckdive, the bottom is 60m, the top of the wreck 40. You can make an easy plan of 15 minutes 60m, then 10 minutes 45. This will give you a diveplan.
Then a cave. Complicated deco in caves is not part of all full cave courses. A full cave course is not a substitute for a decocourse. But some important points have to be told in this courses by every instructor, so when your experience grows you know what factors influences a diveplan in a cave, and how to make a good diveplan. The best caves for a course are shallow as it allows you a lot of bottomtime. A cave is dark, and overhead, so at 2m depth it looks the same as at 80m depth. But follow a course is a really good idea if you haven't done it yet.
I will explain some things:
Rule 1 is: if you can make the dive within the old famous NDL with a nitrox, take a nitrox instead of air. Make a cave dive never more complex than needed. Gasswitches are always more complicated than just stay on backgas with no obligatory stops needed. Obligatory stops on backgas are more complicated than no obligatory stops needed, so choose the right gas. (I don’t start a discussion about deco on backgas here).
Then: Know the profile of the cave (we don’t talk about exploration of unknown caves). A cave is a natural formed ‘thing’, so gives almost never an ideal profile. From most caves you can find maps in books or internet.
And: start with some easier dives in the cave. If possible make some shorter dives to know what you can expect. If not possible then be really conservative.
When not so experienced in doing dives in caves, be carefull with inflowing caves. The way out will always take more time then the way in. Start here with dives within NDL and extra gasreserves.
Next rule: Know your swimmingspeed. Flows can make your speed faster or slower. Easiest to calculate are caves with no flow or outflowing (then the way out is always faster than in, make a plan by using the speed you can get in, then the way out will give you more conservatism). Major restrictions a greater depths will increase your ‘bottomtime’ at depth. This can make you will reach your turnpressure/point earlier than expected. Don’t swim further, but turn. A next dive the cave is still there (and next year and next years), so don’t risk things. The swimmingspeed is needed to know how much time it will take to reach point ‘X’ in a cave.
I will give you some example now of a dive, it is never a substitute for a course. And doing more complex dives in a cave must grow with experience.
So if the cave has this profile, no flow: from entrance to length of 180m max depth 10m, then drops to 23m with length of 250m, then drops to 46m for 100m. You can now calculate the time needed to swim the length of 180+250+100m, to your turnpoint.
BUT you need to calculate the way back too. So without stops it is 2 times the 180+250+100m. If you swim with 10m/minute the divetime is shorter than you swim with 14m/minute. Most divers think they swim faster than they really swim. You must calculate your turnpressure of backgas, and if it is possible to reach the turnpoint within the turnpressurelimits, so calculate if you have enough gas for the dive. If you dive with 10m/minute it will take 53 minutes to reach your turnpoint at 530m from entrance.
Based on the maximum depth you can take a trimix, let’s say a standardgas 21/35. This profile will give you some obligatory decostops, so you must calculate the amount of gas needed to reach the first decostop. Let’s say that is 180+250+100 m for the way in and an extra 100+250m for the way out. The last 180m are on decogases. The profile of the last 180m will affects your stops too. If 150 out of the 180m is at 9m, you will have a long stop of 15minutes at 9m. But you will swim and not stop moving. If the cave is here 10m, then you swim at 10m. If the cave is 8m you have to decide to wait (costs gas), or swim at 8m as deco is no absolute science (and maybe you will have a computer that shows 'missed decostop', so buy a computer that calculates further and not give you the famous 505). And maybe you decide to take a non-DIR gas to swim the last 180m: ean80. There are more options, and it depends on how long a stop is and what is the rest of profile and is there good point in the cave to hold the stop, etc.
For this dive you need to have enough gas for deco, enough backgas, and reserves in case of a lost decogas or something. Etc. Then you have to think where you can drop your cylinders. You don’t take all gases with you like with a wreckdive. If you use a 100% and a 50% for deco you try to drop the 100% at 6m depth (MOD of the gas). And the 50% at 21m depth. As this is a dropoff, most likely your 50% will be dropped at 23m depth (so maybe think about another gas that can be used at 23m too to optimize deco-swimmingrate-divetime). On the way back you pickup the gases again. During the dive check if you are at 180m at the expected time, at 430m at the expected time, etc. And check if you have enough gas as you have calculated. This gives you possibilities for inwater updates.
If the cave has a restriction at 6m depth, then do the last stop at 7m and go up to surface slowly (as always adviced). Holding a stop in a restriction as there are other possiblities is really irritating if others want to pass, so only do it if no other options are there. Same with dropping cylinders. Choose a good position.
Then a cave. Complicated deco in caves is not part of all full cave courses. A full cave course is not a substitute for a decocourse. But some important points have to be told in this courses by every instructor, so when your experience grows you know what factors influences a diveplan in a cave, and how to make a good diveplan. The best caves for a course are shallow as it allows you a lot of bottomtime. A cave is dark, and overhead, so at 2m depth it looks the same as at 80m depth. But follow a course is a really good idea if you haven't done it yet.
I will explain some things:
Rule 1 is: if you can make the dive within the old famous NDL with a nitrox, take a nitrox instead of air. Make a cave dive never more complex than needed. Gasswitches are always more complicated than just stay on backgas with no obligatory stops needed. Obligatory stops on backgas are more complicated than no obligatory stops needed, so choose the right gas. (I don’t start a discussion about deco on backgas here).
Then: Know the profile of the cave (we don’t talk about exploration of unknown caves). A cave is a natural formed ‘thing’, so gives almost never an ideal profile. From most caves you can find maps in books or internet.
And: start with some easier dives in the cave. If possible make some shorter dives to know what you can expect. If not possible then be really conservative.
When not so experienced in doing dives in caves, be carefull with inflowing caves. The way out will always take more time then the way in. Start here with dives within NDL and extra gasreserves.
Next rule: Know your swimmingspeed. Flows can make your speed faster or slower. Easiest to calculate are caves with no flow or outflowing (then the way out is always faster than in, make a plan by using the speed you can get in, then the way out will give you more conservatism). Major restrictions a greater depths will increase your ‘bottomtime’ at depth. This can make you will reach your turnpressure/point earlier than expected. Don’t swim further, but turn. A next dive the cave is still there (and next year and next years), so don’t risk things. The swimmingspeed is needed to know how much time it will take to reach point ‘X’ in a cave.
I will give you some example now of a dive, it is never a substitute for a course. And doing more complex dives in a cave must grow with experience.
So if the cave has this profile, no flow: from entrance to length of 180m max depth 10m, then drops to 23m with length of 250m, then drops to 46m for 100m. You can now calculate the time needed to swim the length of 180+250+100m, to your turnpoint.
BUT you need to calculate the way back too. So without stops it is 2 times the 180+250+100m. If you swim with 10m/minute the divetime is shorter than you swim with 14m/minute. Most divers think they swim faster than they really swim. You must calculate your turnpressure of backgas, and if it is possible to reach the turnpoint within the turnpressurelimits, so calculate if you have enough gas for the dive. If you dive with 10m/minute it will take 53 minutes to reach your turnpoint at 530m from entrance.
Based on the maximum depth you can take a trimix, let’s say a standardgas 21/35. This profile will give you some obligatory decostops, so you must calculate the amount of gas needed to reach the first decostop. Let’s say that is 180+250+100 m for the way in and an extra 100+250m for the way out. The last 180m are on decogases. The profile of the last 180m will affects your stops too. If 150 out of the 180m is at 9m, you will have a long stop of 15minutes at 9m. But you will swim and not stop moving. If the cave is here 10m, then you swim at 10m. If the cave is 8m you have to decide to wait (costs gas), or swim at 8m as deco is no absolute science (and maybe you will have a computer that shows 'missed decostop', so buy a computer that calculates further and not give you the famous 505). And maybe you decide to take a non-DIR gas to swim the last 180m: ean80. There are more options, and it depends on how long a stop is and what is the rest of profile and is there good point in the cave to hold the stop, etc.
For this dive you need to have enough gas for deco, enough backgas, and reserves in case of a lost decogas or something. Etc. Then you have to think where you can drop your cylinders. You don’t take all gases with you like with a wreckdive. If you use a 100% and a 50% for deco you try to drop the 100% at 6m depth (MOD of the gas). And the 50% at 21m depth. As this is a dropoff, most likely your 50% will be dropped at 23m depth (so maybe think about another gas that can be used at 23m too to optimize deco-swimmingrate-divetime). On the way back you pickup the gases again. During the dive check if you are at 180m at the expected time, at 430m at the expected time, etc. And check if you have enough gas as you have calculated. This gives you possibilities for inwater updates.
If the cave has a restriction at 6m depth, then do the last stop at 7m and go up to surface slowly (as always adviced). Holding a stop in a restriction as there are other possiblities is really irritating if others want to pass, so only do it if no other options are there. Same with dropping cylinders. Choose a good position.
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. The divetime of a 530 m distance is 53minutes with 10m/minute and with 14m/minute it is about 38 minutes. 
