Modern research/thoughts on Ascent Rates

[TrimixToo]

As a practical matter for ocean technical diving, ascent rate coming off the bottom and moving up to your first deco stop is likely to be limited by how fast you can wind up the SMB spool. With thick gloves and cold hands, you don't want to risk fumbling it by trying to go too fast.

Assuming you're running an SMB off the bottom. Around here running an SMB off the bottom is sort of a rare thing unless you're in trouble. We mostly go up and down the line the boat is tied into. I think this difference is likely explained by the difference in our diving environments.

I drop as fast as I can, too. Why waste gas on the descent? In significant currents, of course, I go a lot slower in both directions. Falling off the line without a remarkably good reason so the boat has to come get you is sort of, um, frowned upon.

 

[Nick_Radov]

Assuming you're running an SMB off the bottom. Around here running an SMB off the bottom is sort of a rare thing unless you're in trouble. We mostly go up and down the line the boat is tied into. I think this difference is likely explained by the difference in our diving environments.

Sure it depends on the environment. We often dive in strong currents so the boat doesn't anchor or tie into anything. It wouldn't be safe or practical to go up a line in those conditions.

 

[boriss]

As a practical matter for ocean technical diving, ascent rate coming off the bottom and moving up to your first deco stop is likely to be limited by how fast you can wind up the SMB spool. With thick gloves and cold hands, you don't want to risk fumbling it by trying to go too fast.

As a practical matter, if you're launching a DSMB you're already at a depth where this discussion is null and void. Carrying a big reel isn't a problem for these types of dives.

 

[Nick_Radov]

As a practical matter, if you're launching a DSMB you're already at a depth where this discussion is null and void. Carrying a big reel isn't a problem for these types of dives.

Well bringing a reel isn't a huge problem, but since it's not actually needed I'd rather leave it behind.

 

[Wibble]

Sure but then you have to carry the large reel through the entire dive, so it's usually not worth the hassle. Plus when you deploy the SMB, large reels can occasionally bind up due to sand or something getting between the moving parts. So it can work but usually it's better to only use a reel if you're towing a surface float through the entire dive and use a simple spool for launching an SMB from depth.

Of course "it depends" on several things.

Around here — English Channel — it is very rare to "must return to shot line" unless it is foggy so all ascents are on a one per diver SMB. Rebreathers are very common especially when diving with trimix, so there’s not a surplus of gas available to fill the SMB, thus self-inflating SMBs are very common, either of the crack-bottle or one use CO2 cartridge.

For a reel, you must launch the SMB from the wreck so the skipper can count the divers off the wreck and follow the field of blobs downstream (currents can run up to 3kts) as everyone decompresses. This means that 100m/330ft reels are needed if diving to 60+m/200+ft. Finally, we tend to use man-sized Kent Tooling or Custom Divers reels as they’re strong and reliable.

The SMB is bungeed to the reel and that is clipped to the bottom of the rebreather and rests on top of the RH bailout cylinder, out of the way. If there’s only one bailout then it hangs beside my waist belt, so neat and not a snag risk.

My backup Halcyon SMB is on a 60m/200ft Apeks spool as it compact and lives in my drysuit pocket. Also carry a small yellow SMB for emergency alerting the surface.

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[Rich1280]

And slightly further down the coast in Portland (Dorset, not Oregon, 100 or so miles) we can use one DSMB per team, and get them launched between 30-21m as we ascend from the wreck at a decent rate. I've never had complaints about the Halcyon 6ft Slim, launched off a spool. Even if the skipper wants a bag per diver, we just launch one bag, then each clip a small 3ft bag to the same line to send it up. Reduces the risk of cats cradle, and everyone happy. This is for CCR diving down to 60m or so.

Rich

 

[JonG1]

And slightly further down the coast in Portland (Dorset, not Oregon, 100 or so miles) we can use one DSMB per team, and get them launched between 30-21m as we ascend from the wreck at a decent rate. I've never had complaints about the Halcyon 6ft Slim, launched off a spool. Even if the skipper wants a bag per diver, we just launch one bag, then each clip a small 3ft bag to the same line to send it up. Reduces the risk of cats cradle, and everyone happy. This is for CCR diving down to 60m or so.

Rich

Genuinely interested Rich, can you hit/maintain a 10m a minute ascent to the smb launch depth?

We generally ascend on the shot/lazy shot/trapeze and it can be quite a challenge even with the line to hit the 10m/min rate.

 

[Wibble]

And slightly further down the coast in Portland (Dorset, not Oregon, 100 or so miles) we can use one DSMB per team, and get them launched between 30-21m as we ascend from the wreck at a decent rate. I've never had complaints about the Halcyon 6ft Slim, launched off a spool. Even if the skipper wants a bag per diver, we just launch one bag, then each clip a small 3ft bag to the same line to send it up. Reduces the risk of cats cradle, and everyone happy. This is for CCR diving down to 60m or so.

Rich

Curious how you inflate the SMB when diving CCR -- suit inflate or bailout tails?

Main reason I moved to a big reel and self-inflating SMB was to take away a load of the hassle of launching a SMB as the ascent on a CCR is so busy, anything for an easy life is good. The heavier reel also smooths out the bumps from waves on the surface. The other dirty secret is the heavier reel can help if you have a little buoyancy hiccup - the weight of the reel can be used to pull yourself down rather than dumping gas or finning down.

 

[inquis]

The other dirty secret is the heavier reel can help if you have a little buoyancy hiccup - the weight of the reel can be used to pull yourself down

Since buoyancy already includes the effect of the reel, this doesn't make any sense to me.

 

[Wibble]

Since buoyancy already includes the effect of the reel, this doesn't make any sense to me.

You don't hang on to the reel as it's bouncing up and down to the beat of the waves above. You either let it bounce a couple of metres / few feet in front of you or let a bit of string out and let the reel bounce below you and let the string go up and down between your forefinger and thumb (I sometimes use a double ender so it doesn't saw into my drygloves). Thus you're not holding the SMB nor reel.

If you have a buoyancy fart, you grip the line and either use the weight of the reel to pull you slightly down, or the buoyancy of the SMB to pull you up a bit until it's stabilised.

OK, some people hang on to their SMBs and are a bit negative. Not keen on that myself, but it's a free world so they can fill their boots. It's a bit naff if there's waves above.