Planning an unplanned dive

[Foxfish]

Most of the dives I do are from a charter boat. Our dive plan is to jump in and explore the reef structures then get to the surface with 50 b in the tank and back on the boat within an hour. I'm interested to hear some of the gas planning and navigation techniques people use for this kind of diving.

We dive about 20 km off shore in an area of about 100 km2. There are hundreds of different places you could drop the anchor and dive so we're often diving different locations. Depths range down to 30 m but around 20 m is more common. The boat is 30 m long and we have up to 40 divers at a time. The dives are unguided. People buddy up, jump in and go where they want.

We have a dive briefing a few minutes before jumping in the water and never plan a route for the dive. This is a given and will not change. You cannot pre-plan the route you will take on a dive except maybe agree on some vague directions you will head at the start. We get given vague directions to the best locations on the site and the depth range. Apart from a bit of surface current at times there is no problem surfacing anywhere you choose. The skipper is careful to avoid locations where there are boating hazards or strong currents. If a diver ends up too far away they can be picked up by an inflatable but I've never seen that happen.

I've dived like this off the boat for a number of years and some of the old time regulars have clocked dives numbering in the thousands. I've never seen an incident worse than someone being sea sick.

 

[mala]

sounds like the plan you are using is the right one.

 

[dumpsterDiver]

How lost can you get with 40 people swarming over the reef?

 

[Akimbo]

Recreational dive plans are very different than a commercial or technical dive plan. Meandering dive profiles that culminate by running low on gas or approaching NDL are the most fun and least stressful, unless you have a particular objective for the dive.

 

[Eric Sedletzky]

Sounds exactly like the diving we do off charter boats in Southern California.
It's the free-est charter boat diving I've ever done. Basically, they pull up to a spot, tell you a little about what you might encounter terrain wise in each direction, then open the gates and the pool's open. You can solo dive, buddy dive, looky loo dive, hunt, take pictures, whatever you want.

 

[Donnah]

How lost can you get with 40 people swarming over the reef?

Once in Belize ten of us got lost together. No one had any idea where the boat was. The sun had gone behind a bank of cloud and it had gotten darker. My husband went up, saw the boat, took a heading, came back down. We had all been going in the wrong direction. Then, we were saved. We saw a DM with a diver holding a slate and compass (navigation course). We followed them. When it got so shallow we could almost stand up, we realized we were almost to the shore. The captain couldn't figure out why all the bubbles had passed the boat and kept going. There were some words said when we got back to the boat. We had all been doodling along, looking at fish, paying no attention to where we were going. No one was low on air or in any trouble. We had a good laugh, and that night toasted the gal taking the navigation course -- she was lost and the instructor was letting her discover it on her own.

 

[MXGratefulDiver]

Sounds exactly like the diving we do off charter boats in Southern California.
It's the free-est charter boat diving I've ever done. Basically, they pull up to a spot, tell you a little about what you might encounter terrain wise in each direction, then open the gates and the pool's open. You can solo dive, buddy dive, looky loo dive, hunt, take pictures, whatever you want.

I've done a bit of that style of diving down there ... off the Peace. But we normally bring along scooters. I remember one dive where we didn't ... almost everyone on board ended up having to get collected by the inflatable and brought back to the main boat, due in part to currents that were taking us farther and farther away from the boat. This was up around San Miguel, in the northern Channel Islands.

... Bob (Grateful Diver)

 

[D_B]

I take into account of depth of dive to calculate the reserve gas that is rquired to get a buddy and I to the surface , point in planned direction and set the reverse bearing on compass to the boat for return , and take into account any bottom contours (mentioned in briefing) for direction planning ... take gas reading when assembled on bottom, subtract reserve gas and use approximately half of that going out before turning back .. most times with plenty of gas for just tooling around under the boat

This is what I use for planning, a rule of thumb from Lamont's Rock Bottom For Recreational Divers .. Remember, it's only a rule of thumb for calculating the reserve gas needed to get you and a buddy to the surface, but it works for me for recreational depths
Depth in PSI+ 0 + 300psi = reserve pressure (example: 80ft + 0 = 800psi + 300 psi = 1100psi to start ascent

 

[RJP]

Our dive plan is to jump in and explore the reef structures then get to the surface with 50 b in the tank and back on the boat within an hour.

While that may be "a plan" of sorts - and a great many people do nothing more than that - the idea of "jump in, swim around, come back" isn'tmuch more of a plan than saying "the plan is to not die.

At a minimum I'd like to include specifics around depth, gas needs/management, turn pressure/time, and something more than "explore the reef structure" as part of the plan. Doesn't need to be much, but something like "We'll drop down to 50ft, see if there's current, if not we'll head left along the bottom of the reef. (if current, we'll head into it) for 20min or when one of us hits half a tank. At that point we'll come up to the top of the reef at 40ft, reverse directions and head back to the upline. When we get to the upline, we'lll check gas and burn until 75bar, 50min, or NDL and then head up so we're back on the boat with 50bar and withing 60min"

Not complex, and can be discussed with buddy while putting fins on and jumping in, but makes sure everyone has the same understanding of what "the plan" is.

 

[Steve_C]

I prefer to not have a long surface swim or wait on the surface or to pop to the surface in more than 10 meters. With no specific target I tend to run a figure 8 where I go out, find the anchor, then go out in another direction, find the anchor and then spend the last bit of the dive in the general anchor area.