first of all this advice is for saltwater salmon fishing only....
now i have the feeling ive made an ass of myself on this website before.... but this is something i have learned while trying to catch fish in the sound to make ends meet and keep my jeep from being reposesed.... this is what i have learned.... professionally.
alright so im going to give away some advice that is mind bending, totally contradictive to alot of thought, and to be honnest, it has saved me several 1000$ in equpment and hours of time..... this is professional advice from comercial fishermen that i have collected over the years. save yourself the stress of buying an expensive fish finder, and learn how to do things the simple, most lethal, cost effictive way....
all a fish finder does is shows you the depth and where POSSIBLE fish are.... here in the puget sound... a 35lbs king salmon has the same ping as a 10lbs jellyfish....
after gillnetting for countless months in the sound and using a "fish finder", the monster "fish" or "bait ball" shows up on the fish finder exactly the same as a huge hoard of jellyfish...
YES JELLYFISH.... they will F up your fish finder readings unlike any other.... and having to haul a gill net in up to 10 times a day, you will find that the "line" on your sounder that appears to be a HUUUUGE bait ball.... can be nothing more than a hoard of white jellys......
even on 8000$ top of the line commercial units, a "fish" can range from anything from a monster king to a submerged log.
there is no such thing as a "fish finder" that will tell you "king salmon 300 feet ahead 90 feet down", all a fish finder does is say there is SOMETHING roughly 90 feet down.
what i have learned:
when fishing downriggers, ALL YOU NEED TO KNOW is the angle of your downrigger wire in relation to your down rigger ball. there is a book about this. i forget the title, but it basically states that with a 15lbs ball, if your downrigger line is at a 45deg angle, you are at the the most efficiant fishing speed.
SPEED..... many downrigger fisherman worry about the speed of thier lure (not the boat, but the action of thier gear).... the simple fact is.... if you can find the chart that relates ball weight to depth to angle of downrigger wire it equals optimum speed. screw gps speed, screw nautical tachs. angle of wireXball weight/depth= speed
SECCOND
ALL FISH HATE LIGHT.
what that means.....
many of you have noticed, certain colors work better in early hours many use pinks, reds, yellows, light greens in the early hours and dark greens, glows, purples, whites in the mid day to late evening hours, and repeat early morning colors to late evening-sundown.... well, go read up about the color spectrum..... the simple fact is salmon hate light.
every color will disperse to almost invisibility status at its appropriate depth
you have to adjust the color of your gear according to the depth that the salmon swim to provides comfort to thier eyes....
the fish dive to the changing light conditions of the day. when its darkest they are on the surface.... when the sun is at high noon, the fish hide in the deep dark.
light hurts the fishes eyes..... so they go deep.
remember ROYGBIV the same applies to what depth the colors fade from the fishes eyes. for exapmle at high noon, a red hoochie will be invisable to a fish at 50 feet. where as a purple will be good to almost 100 feet.
read up in what colors fade at what depth. once you figure that out, you can start to figure out what colors fade at roughly about what time of day depending on light conditions.
fish finders are a joke. the most important thing you need to know is what gps topographical line to follow....
all a fish finder does is provide you the depth under the boat, but a gps will show you the ledges and ridges the fish will hide behind/under.....
using the downrigger angle/ball weight formula and following the contures of a gps line combined with the time of day and at what depth colors fade from the spectrum............... that is derby winning, money making, fish slaying facts.......
thats why i claim to god my 85$ eagle cuda 168 fish finder that i bought at WALMART will out fish any other fish finder out there.... it tells me the depth and thats all i need a unit to do........
this is my

but ill be damned if somebody comes up with a more effictive cost eccificant way of fishing on the salt
time of dayX at what depth lure colors fade X angle of downrigger cable DIVIDED by downrigger weight.....
find the official formula.... and you guys will learn 1000% more than even comercial fisherman
its as simple as that