Finding and marking a good dive site is an important skill to have. If your site is now then prepare yourself for an exiting exploratory adventure.
Use the GPS
Most wrecks have a Lat/Long reference, some of the older references may be in degrees, minutes and seconds (04O.12'. 30"), whilst the same position in more modern references (degrees, minutes and hundredth of a minute) might look like this 040.12'. 50"
Whilst most GP's use similar operational principles to become skilled, you need to study the manual and practice.
Use the echo sounder
Read the manual available for basic operation but experience counts. Get used to display and what to look for on good sites. Biggest thing to understand is effect of different seabed depths. For example, if scanning 40m deep, even small lumps in trace may be interesting. If only 6m deep, even big lumps can be small boring rocks.
When pinpoint accuracy is required, remember that the reading you see is from the transducer, which is normally located at the rear of hull, so your RIB has already passed over whatever is displayed on the screen. If you're putting down a shot line, you may need to do several passes to get the best possible position.
Don't forget that big images on the screen could be divers or even bubbles.
Find interesting seabed
It is far better to get local knowledge of good places to dive; the Internet, magazines and books are a good place to start. Otherwise look for a variable seabed depth, the more varied the better. As you cross a potential spot keep an eye on the digital depth as this can give a better indication than the trace. Drop off's are usually interesting, as a rule of thumb, these usually follow the contours of the land, so heading towards land or away from it should give you some interesting readings. Normally, steeper walls are better than gently sloping drop-off's, so try to find the most sudden changes in depth. When dropping divers in, make sure they know whether they are on the high part or low part, and which direction to head to get to wall.
Find a wreck
There are masses of information on wrecks; examples include books, Internet, magazines, charts etc. These will provide details of GPS bearings, transits, depths and slack water timings.
Once you are in right area, set up a search pattern, crisscrossing the area. You can use a temporary shot line or lobster pot as datum or use the GPS plot mode to see where RIB has been. Watch the echo sounder all the time, as soon as you see a large mass, turn and crisscross the wreck and identify the centre of the wreck or the best place for the shot line.
Once located and you are sure that no divers are down on the wreck, drop the shot. Lobster pots buoys can sometimes indicate where the location of a wreck and some large wrecks can be identified by a different and distinct area of water as the current runs over the wreck. Remember to look up current from this area.
Transits can also be used, if your eyesight isn't too bad and the wrecks are close to the shore.
Another technique for is the 'drag n snag', Get your shot line ready with a grappling hook at the bottom, drop the hook overboard so it is at the right depth and move forward slowly with the current. When it snags, let go and hopefully it will be on the wreck. The first divers down should make the shot secure so it doesn't pull of wreck.
Deploy a shot line
This needs excellent timing, a lot of patience and a fast shot. Whilst tracking over the wreck, get someone ready to release the shot. As soon as the wreck appears on the sonar and you are sure there are no divers below, get them to drop it, feeding the line quickly and making sure the buoy(s) don't snag as the whole line plays out.
If there is too much slack line, gently motor the RIB up current, gently reeling in spare shot line, then reposition buoy so the line is as vertical as possible without pulling shot off wreck.
This is also useful if the current is running too fast too, as on release the buoy will be pulled under water but will reappear when the current slackens off.
Secure the shot line to wreck
In calm conditions with experienced divers, there is no need to do this. If there is a risk of a current building up or of divers pulling the shot off wreck, it is best to secure it.
The first pair down should descend without pulling on the line. At the bottom, tie off the shot with a waster. If the shot weight is an anchor/grapple, it is better still to loop the anchor back up and secure it to shot line by flukes so there is no risk of snagging when waster breaks.
It's a good idea too, if the first pair take a small signal float down attached to the shot line and release it when shot is secure so the other divers know when its OK to descend.
If you don't have a waster, have the first pair wedge the shot into the wreck, then the last pair can release it so it will pull out cleanly.
Retrieve a shot line
The last dive pair to come up, can free the shot completely from the wreck and ascend up the line. Divers then drift with the shot buoy and the RIB tracks the buoy as it would an SMB. It is vital that there is no risk of other divers being left on the wreck before doing this. One method to ensure this, is to make sure the second wave of divers comprises of only one pair.
If the shot is stuck fast, try motoring the RIB at different angles and at same time pulling hard then release totally. If this proves unsuccessful, your next option might be to send a pair of divers down to release it, clearly this depends on depth, available divers and tissue codes etc.
If other divers are in the vicinity or diving the same wreck you could ask them to release it, failing that you could return to the shot with fresh divers.
The last resort is to break the line and leave the shot. If a weaker line was used to tie the shot to the line, the break should be at that point, thus saving the line.
If the shot comes free OK, you can save a great deal of effort by power lifting it using the RIB. Have a large buoy with wide diameter steel ring underneath. Feed the shot line through this and leave the buoy free in the water. Pull the loose end of shot line until it is taught. Then attach it to the RIB and motor off. Water drag will keep big buoy from moving fast and the RIB will pull the shot line through ring resulting in the shot weight coming to the surface. When the weight hits the buoy, just maintain tension and pull the weight plus the buoy to the RIB.
Track divers underwater
As a general rule always use an SMB unless there are very good reasons for not doing so. On a drift dive it is mandatory, tracking bubbles is dangerous even in the flat calm.
SMB's can still give problems especially is they go in different directions or when there is no diver attached, which sometimes happens with delayed SMB's and reel jams. If they do become widely separated it may be possible to loose sight on one of them. The best solution to this is prevention i.e., tell the divers which direction to go in.
If they do separate widely, to an extent, you can manage this by shuttling between, using the GPS to track positions. As soon as this gets too difficult, you must recall at least one pair of divers. It is far too risky just to hope you will be able to find the second pair after the first pair have surfaced and boarded the RIB. Remember safety first; short dives are far better than lost divers.
Recall divers in an emergency
If there are several divers down and divers surface in trouble, you may need to get the remaining divers up in a hurry. If they are using SMB's, approach them very carefully and give three strong pulls on their SMB, leave the immediate area and give them sufficient time to surface, if they don't repeat the signal.
Alternatively you could get close and rev the engine three times and repeat every minute or two until they surface, or use Thunder flash signals.
Book a hard boat
Good hard boats often booked up during the high season, perhaps a year or more in advance, so book early.
Information regarding good boats and skippers can be found in the following areas:
- Internet (see Skippers Web Site ) and scuba based newsgroups. Many skippers now have their own web sites.
- Talking to other divers, clubs, regional coaches and local dive shops.
- Books, magazines and guides.
- Tourist offices.
Next, make contact with the skipper or the business, check dates are available and get an impression of the company or skipper. Make sure you check the following:
- Recommendation for dive sites.
- The price.
- Is the skipper a diver? (if not beware).
- Facilities on board.
- GPS, Radio and Sonar
- Life rafts
- Compressor (check if air included in price or extra)
- Hot drinks and/or packed lunches
- Exit ladder (some are very difficult with twin sets etc.)
- Size of the boat and more importantly the deck space.
- Weather shelter.
- Recommended local bed and breakfast places.
- Number of dives available (some limit to 2).
- Deposit required.
- Booking/cancellation policy.
- Bad weather policy i.e., refunds, safe sites etc. Make it clear that BSAC state that it not safe to dive in over force 4, so agree that if the forecast is five or higher, the trip will be cancelled without penalty.
Typically boats will charge something like £250 per day. This need to divided equally between the divers. If divers cancel, it may become more or too expensive for others. Make sure that the deposit required from the divers covers this amount.
Once you agree on the deal the skipper may send you a booking form and expect the agreed deposit. Read the small print carefully. About a month or so before the trip, ring the skipper and confirm the details.