Wreck fishing
In theory, fishing over the wrecks should be rewarding from a sailing catamaran. No problem getting to the wrecks less frequently visited by the charter boats full of anglers and commercial line fisherman who all need to factor their travel time and fuel costs into a day's fishing over one of the further offshore wrecks.
The method most commonly used by motorised boats to fish wrecks in the UK is to drift over the wreck with the wind and tide. Fishermen drop their lures close to the bottom upstream of the wreck, drift over the wreck and once past the wreck, wind their lures up and motor back to the start of the drift. Drifting like this, it is possible to cover all the ground near a wreck, and repeat drifts that have proved successful. However, quite a lot of tackle is lost on the wreck. Many wrecks have nets tangled on them, and hooks are easily caught in the nets usually resulting in lost tackle. A lot of time is spent also motoring back upstream, and raising and lowering lures. These problems are exacerbated when the tides are running more strongly.
Naturally, a sailing boat can't drift like a motor boat. There'd be too much work getting back upstream. So, I have tried anchoring over the wrecks. This seemed a promising solution - so long as you can anchor accurately just upstream of a wreck so that you can lower the lures close to it, a great deal of time can be saved in not having to wind lures up and down in order to motor upstream. Fish are often very close to a wreck, especially when the tide is running. If you can get your lures where the fish are shoaling, you'll do well. A few metres away, and you don't get much at all. So anchoring accurately is crucial. Fairly close is fairly useless.
With accurate anchoring over wrecks in mind, I wrote some software that queries a database full of wreck details and draws nearby wrecks on a chart. Zooming in to a wreck and displaying the track of the boat, it is easier to place the anchor in the best place. Accuracy is dependant mostly on the accuracy of the GPS (10 metres) and the accuracy of the data in the database (also often within 10 metres). Notice that with just these two error sources, it is quite possible to be 20 metres away from the chosen anchoring position without being aware of the error.
Of course, the position of the wreck can be confirmed by sailing over it and watching the fish finder display. Then the anchoring position needs calculating. Normally, boats anchor using chain as long as 3-5 times the depth of the water. Using this much chain isn't feasible in 50 metres or more of water. However, anchoring over wrecks in deep water is done only in light winds, and the anchor dragging isn't as catastrophic as it might be when anchoring close inshore. So I have anchored using rope and just a short length of chain close to the anchor. In very light winds, 70 metres of scope might be enough in 50 metres of water, but I have used up to 150 metres in stronger winds and tidal streams. If the anchor drags, it is likely to snag the wreck, so the anchor chain is attached to the front of the anchor. The end of the shank is attached to the chain with some strong cord. This is strong enough to hold the boat, but if the anchor snags it is possible to keep on winching the anchor rope until the cord snaps, and the chain pulls the anchor out backwards. This has happened several times, and I haven't lost an anchor yet.
Unfortunately, I haven't caught many fish yet using this method. This is partly due to visiting wrecks fairly close by - within 20 miles of Brixham, just to try the method out. So there were sometimes not too many fish there (other boats fishing the same wrecks weren't getting many either). We experienced some difficulties getting close to the wrecks.
Anchoring in 50 metres of water using 100 metres of line.
Where the lure ends up is of course dependent on the weight attached, but it is very easy to anchor too far upstream or downstream to reach the wreck. Being too far one side or the other doesn't cause as much difficulty, as the boat can be manoeuvred across the stream by adjusting the angle of the rudders, or repositioning the anchor line from the middle of the boat towards one bow or the other to change the angle of attack of the tidal stream.
Anchoring in the wrong place creates a lot of work - it can take 30-40 minutes of hard work to winch up the anchor from such a depth (we don't have an electric windlass, as this is expensive, and would also require us to have a generator). Anchoring at the wrong time is also not good - if the tidal stream is beginning to change direction, you'll soon be in the wrong place.
There are still possibilities with this method - where the water is less than 60 metres or so, and where the fish finder has shown that there are large numbers of fish on the wreck, and if the wind is light and if the tidal stream will stay steady in direction for 2-3 hours at least.
We won't find one method that works in all situations. Anchoring over wrecks is just one method that at times will be useful. Experimenting with drop-lines and something like longlines while anchored at wrecks has proved fruitful. See longlining.