Using a Downrigger & Fish Finder
Downriggers are great tools when fishing from a boat in large water bodies. They are designed to help fishermen get their lure/bait deeper in the water than they can when using a standard outfit on its own. Downriggers allow the line to be attached to a large lead weight (usually called a “bomb”) that can be lowered deep in the water column. The line will detach from the weight if a fish bites or the line becomes snagged.
Downriggers are mainly used when trolling, but can be used to catch fish while drifting. Most people use downriggers to troll lures. It is also possible to use live or frozen baits, such as small bait fish or yabbies, where this is permitted (for example fishing with live finned fish is illegal in notified trout waters).
Downriggers generally have a depth counter so you know how far you have dropped the lure.
Downriggers do make fishing more dangerous as it is possible to get your system caught in submerged objects or around the propeller. Downriggers have caused serious injuries and death to users in cases where they have been used incorrectly.
Fish finders (sometimes known as depth sounders or sonar) are a great tool to use in conjunction with a downrigger. They cost as little as $100 and give the user information such as the water depth, water temperature and show how far down any fish located under the boat are holding.
If you have a good sounder and read the product manual you should be able to determine what structures and material are on the bottom (such as weeds, mud, sand, rock or trees), how big and what general shape the fish displayed are (you may be able to differentiate between the size and type of fish) and zoom in on a particular water depth for a more accurate picture of the fish at that depth.
I like to setup my sounder so it shows the downrigger bomb on the screen.
Here are a few websites with info on using fish finders
If you have a fish finder pay close attention to the screen to ensure you keep the bomb of your downrigger at least 3m clear of the bottom at all times. If you do not have a fish finder, stick to deep water and do not troll with the downrigger bomb closer than 8m to the bottom.
Most fish (both native and trout) are caught with the bomb set to a depth of about 15 feet. Rainbow trout are a very common catch at this depth. It is unknown why so many fish are taken at this depth, but it is certainly a good spot to fish in most fresh water lakes in New South Wales.
Fishing along old creek lines and steep drop offs with a downrigger also works very well. Bigger brown trout and murray cod tend to hold close to the bottom. These fish also like structure so look for holes or hills on the bottom. Avoid trees as they are very bad news when using a down rigger.
When downrigging you can use any lure you would normally fish, but you must consider how deep each lure dives when you set your depth.
Ask your local tack shop for advice on using downriggers and fish finders before you buy one as they need to be suitable for the places you fish and the type of boat you have.
There are also may books on the subject of trolling that have a great deal of valuable information.