Techniques for boat diving without surface support

[tylerdives]

I'm aware of the thread "Boat Diving With Nobody at Surface;" however, I'm interested in hearing how those that do boat dive without surface support mitigate the risk (and frankly, I'm just trying to get to the minimum thread count to post gear for sale on the classifieds).

Personally, I dive off of a 16ft Zodiac and limit myself to only very good conditions (wind, waves, and current). I also carry a PLB as well as visual and audible signaling devices (giant SMB and whistle).

Most often, I am wreck diving somewhere that has a mooring (usually only one mooring per wreck around here). I tie in from a bow cleat and then also attach a (large) spool of 5/32 Dyneema to the bow eye (dampened with bungee), which I spool out on the way down, being careful to inspect the quality of the mooring line as well. Somewhere above the wreck, I attach a small weight to the Dyneema line and let the line out so the weight is directly underneath the boat (down wind/current). Then I tie the spool off to the wreck. On the way up, I just do everything in reverse, spooling up as I go. As I see it, the benefits are: - redundancy over the single mooring line, and drawbacks are: - potential entanglement hazard for other boats with lines between my boat and the wreck (which is very unlikely, and still the case with the single mooring line), and also potential for the spool to wrap around the mooring line in light/variable wind/current (I can always unwrap it as I ascend).

Less often, I am diving a medium distance from shore over rocky bottom. I drop an oversized anchor with a minimum of 7:1 scope, dive the anchor, and reposition as needed to secure it. Usually this means wedging it under a rock, between boulders, or tying the chain on to something.

My least frequently used and least favorite anchoring method is in sand. I am only over sand when I am very close to shore. I just put out a ton of scope.

Are any of my mitigation techniques liabilities than I haven't realized? What do you do?

 

[MaxBottomtime]

I watch the swell models for a few days before diving, knowing that they are often wrong. We have several live beach cameras that I check before going out. We have all chain for our anchor and always anchor next to the reef/wreck so we can find the anchor before each ascent. We don't go out if the swells are over three feet or close together, and we don't dive in current or on windy days.

We would not go out today.

 

[Tom_Ivan]

I frequently dive without leaving someone on the boat. My personal rules are;
Only in very calm waters
Only dive within swimming distance of the shore.
Always set the anchor at the start of the dive
Use a guideline tied off to the anchor to guarantee that you navigate back the boat.

 

[fullytek]

Extremely bad idea

 

[Still Kicking]

Personally, I dive off of a 16ft Zodiac and limit myself to only very good conditions (wind, waves, and current). I also carry a PLB as well as visual and audible signaling devices (giant SMB and whistle).

How much chain do you use? Chain is as important -- if not more important -- than the size of the anchor for holding power. The weight of the chain keeps the anchor shank parallel to the bottom and allows the flukes to properly bite. A claw or plough style anchor is best if you anchor in a variety of seabeds IMO.

Having said that, a 16' inflatable won't exert much force on the anchor so you can get away with somewhat lighter ground tackle than boats with a higher profile. I used to use a 5kg Bruce and about 15 feet of 1/4 or 5/16 inch chain with 200' of anchor line.

I would not intentionally wedge or trap the anchor -- if you get back to the boat and can't dive down to the anchor for any reason you have created another problem for yourself. I just go down the anchor line at the start of the dive and verify the hook is holding but can be picked up easily at the end of the div

As for other protocols, it sounds as though you are on the right track. Pick your day and be prepared to scrub any dive if you are not 100 percent comfortable.

A scooter is a nice option to help you get back to boat but they are never 100 percent reliable so I keep my plans conservative in all regards (no current, no deco, inshore etc).

 

[Tim Clark Diving]

Anchor issues are the most common issue I have seen with leaving the boat. Still Kicking gave great advice, but you also need to dog down the shackles. Use a piece of stainless steel wire to secure the pin to the shank of the shackle. Otherwise, the shackle can work its way out during your dive and your whole anchor system can come apart.

 

[Waterwulf]

We dove from my boat with no one left aboard regularly when I was a teen but we took precautions. The anchor lines were checked over every time. We used two anchors and both were checked when we dove down. We always filed a flight plan and the boat had all of the right gear. We used a dive flag and maybe the most important thing of all, a drag line with buoys on it. A hundred yard line with buoys along it tailed out in the current over the stern of the boat gives you some room in case you miss the boat on surfacing.

 

[MB NZ]

There's a nice video on YouTube of how to use two anchors. The first is deployed on a fixed length rope, the other end of which is firmly secured to the chain of your regular anchor. Once connected, the second (regular) anchor is deployed in the usual manner. I haven't tried it yet, but it seems to be a common technique used by yachtsmen.

 

[Still Kicking]

I only use a second anchor on overnight stays. I set a stern anchor if i am worried about the wind shifting and the boat swinging in a tight anchorage during the night.

Only use a stern anchor if all the other boats in the anchorage have them also -- if every other boat swings on a wind shift and one doesn't, you can end up with a collision in the night.

 

[tylerdives]

How much chain do you use?

I believe that on my Zodiac I have >= 10ft of 5/16"... more would be nice, but the anchor locker is not large. Due to the very limited conditions in which I will anchor without surface support, I never see the chain lift from the bottom. If I was really concerned, I might put a weight further up the the anchor line to act as a snubber and to increase the incident angle of the rode, but I likely wouldn't be diving in such conditions anyhow.

I would not intentionally wedge or trap the anchor -- if you get back to the boat and can't dive down to the anchor for any reason you have created another problem for yourself.

I've debated this with myself once or twice and value your advice. In the scenario where I don't ascend from the anchor and surface without enough gas to dive the anchor (neither of which has ever happened), I'd rather just drop the anchor line than have the boat float away. For what it's worth, I do try to consider the anchor's ability to release when pulled vertical.