Trolling..
Trolling lures or bait behind the boat is where the catamaran could excel. The width of the boat ('pod' is 6 metres wide) allows for using several lines, without necessarily using poles from the sides of the boat. Poles could be used optionally, as the mast makes it easy to support them. No fuel used, no noise.
..for tuna
Albacore tuna can be found along the edge of the continental shelf from July - late October right through the Biscay and north towards Ireland. A report compiled by Seafish in 2005 on the feasibility of trolling for tuna is available here.
It's 300 miles or so from Newlyn to the fishing grounds. The technique consists of sailing at around 6 knots, towing lures behind the boat. A sailing boat can do this almost as well as an engined boat.
A limitation of the catamaran is the load capacity. It will take 2-3 days to sail back to Newlyn with the catch. The ice has to last until we reach port, so we'd need to set off back with a maximum load of 600 kg of tuna to allow for 400 kg of ice. With 6 days sailing time getting to the grounds and back, and say 3 days fishing. There'd have to be at least two people on board to keep a 24 hour watch. Will the price we get for the tuna pay for nine days (minimum) work by two people? At current prices, probably not. However, if we were to be offered an improved price taking into consideration the zero-carbon price of the effort, and the fact that the fish will have been on ice for between 3-6 days (larger boats stay out for up to 14 days), we'd like to give it a try.
..for other fish
Trolling for tuna involves towing lures at or just below the surface at 6 knots. Trolling for cod, pollack, ling and bass requires a speed of around 2 knots. But the lures need to be close to the bottom.
The way to get a lure down deep while trolling is to use a downrigger:
When a fish takes the lure, the fishing line is released from the downrigger.
Downriggers are commonly used in the USA, in the Pacific NW for salmon, on lakes and around Florida and the SE coast of the USA. Downrigger cable is usually stainless steel and is kept on a reel on deck. It is raised and lowered manually (hard work) or electrically (expensive). When a fish is caught, the downrigger needs to be raised at the same time as the fish is reeled in to avoid tangles. Downriggers need to be raised and lowered as the water depth changes.
I have adapted these ideas for trolling under sail, and plan to experiment with it in 2010. My plan is to enable fishing with several downriggers at once, to avoid raising and lowering the downriggers and avoid having to raise the downrigger when a fish is caught. Further, raising a 3-5 kg fish from a depth of 50 metres as it is being dragged behind a boat at 2 knots is a lot of work. Raising 100's of kilos that way isn't feasible manually and is expensive to implement electrically. I have a plan to do it with basic home-made equipment...
First, the downrigger weights. Typically a lead ball is used. What we ideally need is maximum weight for a minimum drag. A ball shape doesn't do that. A fish shape does. Or a submarine shape. Or the shape of a sash window weight if it is held horizontally.
Cast iron cylindrical sash weights with rounded ends of varying weights are available in any quantity from my local recycling centre. They can be used suspended horizontally in the water, and kept pointing in the direction of travel by the addition of a fibreglass tail:
Next, the detail of the release system:
The downrigger line is threaded through a hollow fishing float. An elastic band is attached to the top of the float, and the fishing line with a small lead weight attached to the top of the float. When a fish strikes, the elastic band is broken leaving the small weight on the fishing line. The float rises up the downrigger line to the surface where it can be retrieved and reset with the fishing line once the fish has been unhooked.
And further, a sail-powered fish retrieval system!
If the boat is trolling a 2 knots or so, the fishing line is released from the downrigger when a fish strike causes the elastic band to break (there are commercial release mechanisms available if elastic bands prove too basic).
A block on a rope is attached to the fishing line, and above that, a drogue. The drogue is thrown into the water, and the drag on the drogue as the boat sails through the water pulls the fish up. The rope is needed so that the fish is pulled up to the surface some way behind the boat, clear of the downrigger. Once the fish is close to the surface, the fish is pulled in the last few metres with the rope, and the drogue is retrieved with a floating line attached to the back end of the drogue (not shown in diagram to keep it simple). The drogue will collapse pulled in backwards, and the drag will be slight.
Note that if the fish is pulled up only slowly, it is straight-forward to send another fishing line down the downrigger with the block that is lifted to the surface by the float once the fishing line has become detached. This ensures a new lure is in place as soon as possible.
A simple method to get rid of the requirement to raise and lower the downriggers as the depth varies is to keep the depth constant - that is, sail around depth contours. This is easier than it sounds. The catamaran has an Autohelm self-steering device, which can take its course instructions from my navigation software on the laptop. Setting a course along a depth contour is just a matter of creating a route in the navigation program by clicking a series of waypoints on the chart, saving the series as a route, and making the Autohelm follow the route. It sounds complicated explained like that, but it really only take a minute to set up.
Software for trolling
A program I wrote myself for displaying the positions and details of wrecks, I have just adapted to record fish catches. When we are fishing, we can use the laptop in the bridgedeck via a wireless keyboard. The fishing program has details of numbers of lines being trolled, and what lures are used:
When a fish is caught, just 1, 2 or 3 is typed on the keyboard, then the fish is hauled in and the line reset. Pressing one of these keys pops up a panel like this:
The position is read by the computer from the GPS input, and the time, date and which lure was being used is logged automatically. As we have time, between dealing with the fish, it is quick to use the selects on the form to add the fish species and weight. Hitting the Save button enters all the information into a database and gets rid of the form. Several forms can be triggered if we catch a lot of fish at once, to be filled in later when we weigh the fish and put them on ice. There is space for filling in the details for more than one fish because often a line might have several lures or baits attached.
Hitting another button displays the fish caught on a chart. The fish displayed can be just the fish caught in the last hour, the last 4 hours, all the fish this trip, or all fish ever caught on this boat. This way we can sail again over productive areas, we build up maps of every single fish we catch, and as we return to port we know exactly what fish we have to sell. We may use this information to sell the fish directly to restaurants and shops before we even get back to port, so that fish can be delivered directly from the boat to the customer as soon as dock. This neat trick can wait though, till the numbers of fish we catch warrant the extra effort. Till then, we'll continue to sell our fish on Brixham market.