Adjusting Fishfinder

[sunfish]

I spearfish from a kayak and use a Garmin 340c sounder. (dual frequency and dual beam). The fish alarm recognizes three sizes of fish and I have it set only to beep on the largest. This means if it beeps for a fish signal the fish will be over 2lbs. Can anyone tell me a way to adjust it upwards so it only beeps on fish around 4lbs and up?
Will turning down the "gain" affect this?

[dave]

I am very dubious about the "fishfinding" abilities of sounders. I find it is better to turn the fish id off (as it removes the clutter of little fish shapes from the screen) and learn to interpret the arches.
A sounder is primarily for finding structure ,and telling you there are fish of some sort around it. The only way to find out if big individual fish are about is to go and look
cheers
dave
Spearguns by Spearo uk ltd finest supplier of speargun, monofins, speargun and freediving equipment

[sunfish]

This is what I've rapidly found out. I bought the fishfinder to look for structure rather than fish anyway, and it's great at this. It also lets me drop anchor on a shallower bit of reef, so if the anchor's stuck after a long tiring session, it's less of rave to get it loose.
It is useful still to know when a few fish are present, but in my experience, a shoal of medium fish may well mean a bigger one is hanging around somewhere. A shoal of small fish almost never has a big one around. I guess you're right about the arches and this is my best way to go with this.

[foxfish]

Dave is right, I have a raymarine digital fish finder that is meant to be as good as they get, even to the extent of detecting flatfish buried in the sand! Well after looking at the many thousands of fictitious fish it keeps showing I also turned off the fish id!

[miles]

Hiya

As all above has already indicated, switch off your fish ID. Most of my cheaper inshore echo's, Garmins, Eagle, Hummingbird, Lowrance and Navman units wouldn't read fish very well. Not a problem, as, like yourselves, i merely bought them for reading structure on the bottom.

On my commercial boats, Koden and Furuna worked BRILLIANTLY!! On my Furuno, i can tell you what species is showing on the echo. It'll show a single 50kg yellowfin or a single 1kg reef fish on the bottom. Unfortunately, such units normally costs more than what my recreational boat would cost!! So, they're only used for commercial purposes, where one can warrant the expense!! To put it into perspective, a Furuno Colour echo costs about 10 times more than a entry level monochrome garmin/navman/etc/etc.

There are a few reasons why echo sounders read incorrectly. PLACEMENT of the transducer is CRUCIAL!! Often, the unit will pick up the thermocline and show it as fish, especially if your fish ID is "on". Kelp and weeds also thwarts the echo quite regularly. Baitfish also play havoc with your fishfinder!! Small schools of bait spread out sparsely, dense schools of bait, etc, etc will all show up differently. Play around with your "gain", might make things a bit better on your unit.

Another value-able tool is the bottom zoom function. MOST echo's have it and it gives you a much better picture of the bottom. Once again, play around with your unit, you'll be surprised at how fine tuned you can get it!!

Regards
miles

[foxfish]

Hey miles you mention the placement of the transducer, it would appear most guys have mounted their transducers "inside the hull" Where do you consider the best placement?

[miles]

Hiya

You get two types of transducers. A Thru-hull and a Transom Mount.

Thru-hull. Its exactly what its name says, it shoots its beam, THROUGH the hull. As mentioned above, its very easy to install, just put a BIG blob of silicone on it, making sure there are no air bubbles in the silicone and then press onto the hull of the boat. Not so easy to do on most boats, as this would neccesatate cutting a hole in your deck, to get to the bottom of your hull. Placement is very important. You have to put it in a place thats very stable and which is covered by water all the time. On my boats, i like mine place right at the back, maybe half a meter away from the transom. This part is always in the water and even if the boat rocks in swells, it will not get any air between the hull and the water. On my current boat, my Furuno FCV 585 (temporary unit, i was awaiting Furuno's Navnet 3D's release), will read bottom up to speeds of 34knts. After that, it still reads the bottom, but with gaps, which is when air finally gets under the boat, between the hull and the water.

Transom mounts are easy too. The instructions will tell you EXACTLY where to place it on the transom. Once again, you don't want air to come between the transducer and the water, as this will give you a blank reading on the screen. Usually, it'll be mounted very close to the bottom on a v-hulled boat, with less than 1cm protruding on the bottom. Merely playing around with the placement of the tranducer will make a BIG difference in its performance.

Don't know whether i've explained that well enough....

Regards
miles

[foxfish]

Thanks Miles but the trend, it would seem, is to silicone the standard external (transom mount) transducer on the inside of the hull!
I am still a little dubious about this but there are plenty of people doing just that!

[sunfish]

Originally Posted by foxfish

Thanks Miles but the trend, it would seem, is to silicone the standard external (transom mount) transducer on the inside of the hull!
I am still a little dubious about this but there are plenty of people doing just that!

I did just that Mart and it works perfectly well. I made a ring of plasticene and shot a whole tube of silicon into it, then pressed the transducer in and weighted it down with a 2 kilo dive weight. If I was doing it again I'd use less silicon as it took almost a fortnight to set.
At least I know there's no gap in the firing window.
Since the hull is polythene and I use it in water less than a hundred feet deep I use it with the gain turned down to around 50%.

[miles]

The downside to this is that you lose the water temp. probe and speed probe. Most of todays transom mounts come with both speed and temp. probes.

I prefer the thru-hull, becuase my boats are moored. If you have a transom mount, you can't paint anti-fouling on it and if you don't use your boat often, it'll get covered with growth.

Through hull is also safer, if you run your boat up onto the beach often. Offers better protection for your transducer.