Mailing List Archive Mailing List Archive
In-Reply-To: <950721212320_38038931@ao*.co*> Decompressing whilst drifting with the tide is common in the UK, since the sea is tidal with only 20-60 minutes of slack water, depending on location and neap or spring tides. The following describes a method often used for wreck diving. Just before slack water starts, the boat drops a 'shot line' into the wreck, with a grappnel or heavy weight on the bottom and a main buoy and a trailer buoy on the surface. Having checked with the echo sounder that the shot is on the wreck, the trailer buoy is used to gauge the tide strength. When the tide is slack enough, the first pair of divers descend, and (assuming the shot is in the wreck), tie the bottom of the shot line to a firm point on the wreck with a sacrificial line, then release a marker float which surfaces to indicate all is ready for the other divers to descend. The second pair in take with them a 'deco station', which is a buoy with suitably long (depends on circumstances) rope with a weight on the bottom, and a cross line teeing off it (say 5-10m long) with a quick-release clip on the end. The diver holds the quick-release clip in his hand and clips it to a loop at (whatever depth suits the dive), say 6-30m, then continues on down for his/her dive. Stage cylinders can be attached to the deco station. Additional deco stations can be taken in by further divers and clipped to the last one as needed. All divers aim to return to the shot line. Reeling off with a distance line, clipping strobes to the bottom of the shot, etc can be used, good underwater navigation skills are useful. On a reasonably intact wreck, with the shot in an easily recognisable position (say right on the bows, or on the boilers or engines), and reasonable visibility, finding the shot is not difficult. The divers ascend the shot line at the end of their dive, doing stops as needed until reaching the clip attaching the deco station(s) to the shot line, then move across onto the/a/'their' deco station. A tag system is a good idea, say moving clothes pegs from a 'down' position to an 'up' position. Divers mark themselves 'down' as they descend the shot and 'up' as they ascend, as they pass the quick release clip. The last pair of divers up, seeing all others marked as 'up', release the deco stations to drift with the tide. When the boat sees the deco station buoys move away from the shot line buoys, the boat pulls up the shot line and drifts/ follows the deco station buoy(s). The deco station down ropes can have loops or rings spliced in to assist clipping-on stage cylinders etc. Once drifting, divers can either hold onto the deco station down rope(s) or float alongside it, as they prefer. If a diver(s) fails to come up the shot line for any reason, he/she/they deploys a decompression bag (delayed surface marker buoy) or lifting bag on a line, from the first stop. The boat then has to follow that as well as the deco station buoy(s), and they can drift apart a long way, so become unpopular with the boat skipper. If preplanned, the boat can drop a buoy with a spare/standby deco cylinder to anyone who sends up a deco bag. When not all divers have ascended the shot line and marked themselves as 'up', at some point the deco station has to be released anyway, normally when the tide comes strong enough to be uncomfortable. It is preferred to carry as much of your deco gases as possible with you. Note that the vast majority of UK wreck diving is done on air only, using twin cylinders, but depths *CAN* be up to 50m or more. The use of a small pony of oxygen for the last two deco stops is rapidly increasing in popularity, especially on the deeper dives, but often sticking to air tables (the Alladin Pro/Monitor 2 computers are commonly used). Dave Wilkins dwilkins@ci*.co*.co*.uk*
Navigate by Author:
[Previous]
[Next]
[Author Search Index]
Navigate by Subject:
[Previous]
[Next]
[Subject Search Index]
[Send Reply] [Send Message with New Topic]
[Search Selection] [Mailing List Home] [Home]