What is a float tube
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Big Fish from Tubes
Safety in Small Craft
Float Tube Sonar
Making Fishing Maps
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Float Tube Fishing in Ireland

Having a really great time fishing from the world's best floating fishing platform

Adding sonar to your float tube
I use sonar in my tube. I have had sonar in it for years. On the very very rare occasion  I go out for a few minutes without it, I feel blinded and ineffective as if I am fishing with a broken rod, or with a hook with no bait on it.
Get ready to join the float tube navy with underwater eyes. You will be amazed at what it will do for your overall understanding of what lies down there ... and your enjoyment of the sport will be greatly enhanced.
Having an electronic sonar unit on board will help you improve your fishing techniques by giving you more information and guiding your presentations. You might not see fish, (sometimes you will) but seeing the bottom where you are fishing allows you to fish better. Very often you will be fishing a certain depth and catch fish. If you have spot that the fish are taking in a limited depth range, use the sonar to stay in the best water.
Fishfinder or Sonar?
The thing about sonar on a float tube is that when you are fly fishing and spinning, you are casting away from the tube, you do not expect to see the fish that you catch. In shallow water not many fish will stay underneath. So we are not fishfinding, we are looking at the bottom.
What we actually want is:
  • a way to learn the deeps, the shallows, and where the dropoffs are located. When you know the location intimately, you fish those spots casting from a little distance away, and catch fish on them.
  • something to look at while the fish are not taking!
  • a reading of depth, and the ability to then fish there, counting the line down until contact is made with the bottom. The advantage? You now know precisely how deep you are fishing for a given number of seconds countdown with that fly, that length leader, and that fly line/backing combination. So if you plan to fish at 18' in 20' of water, after testing, you can do exactly that.
  • identification of bottom hardness in various places.
  • identification of rough and smooth lakebed.
  • while over deeper water - see visible fish underneath, in front, to the side, and behind (but still within the beam cone).
In short, you figure out a new water in 1/50th of the time with a float tube sonar. Whether you continue to use it later is optional.
There are vertical fishing techniques for fish under the boat or tube, and visible on a sonar unit. The main ones are
drop minnow, jig fishing, and drop shot fishing. A quality sonar will let you watch the take below, a cheap one will not.
Which are the essential sonar features?
Each manufacturer has a range of units, each unit has similarities and differences to the others. There are however certain features that you absolutely need. After you have these essentials, you can if you wish, add money to get more features that are nice but optional.
The sonar unit should be:
Compact and convenient to fit on the tube but not get in the way of fishing.  Have a  low-ish power consumption such that a small light battery can run it for as long as a fishing session lasts. Have a clear display screen on which depth and structure are visible with adequate detail. Temperature of water included.
Optional desirable upgrades: Colour if possible. GPS if possible. Side scan if possible.  The upgrades are add-ons that increase the price! If they push the cost too high so you delay buying a sonar, you are hurting your own catches. better to remove a few add-ons off your "features wanted list" and get the unit sooner. It has to be affordable, so you buy it instead of thinking about buying it!

he options tend to take your attention away from the necessaries. The essential features your sonar unit should have are: depth display ( figures), visual bottom chart display with detail of texture, and water surface temperature (figures).  Look for a compact unit with these features. 
If you pirk, fish dropshot style, or vertically fish leadhead jigs for fish directly beneath, a higher definition screen (more pixels) that shows individual fish will be advantageous. To get the detail of seeing your lure beneath the boat, and the location of fish relative to it, increase the power over 1000 watts to about 2000 watts, and make sure the transducer is 20 degrees minimum width so the cone is wide enough so the lure fishes in it and gets displayed for you to see on screen.
Remember however that while fishing shallow water, you cast away from the tube to cover undisturbed fish with a retrieved bait/fly/lure, you are fishing for fish that will never appear on screen due to not being underneath the transducer. Be honest: while lake fishing, how often do you hook fish in deeper than 20 feet of water? Vertical fishing is not really practical in under 25' much of the time, so seeing fish is not realistic, but seeing baitfish shoals well that is another thing and worth a little extra spending cash.
Most of the time while fishing from your float tube, you will be fishing in water less than 20 feet deep. Rarely you may venture out into the 30 - 50 feet range. This means that a sonar unit does not need the same power requirement for instance as an ocean fishing boat. As a result you do not need the most powerful sonar unit for tubing, and this allows you to choose from inexpensive units with a power rating between 600 and 2500 watts peak-to-peak. Staying between 600 and 1500 watts reduces the battery size required to power it up and makes the tube easier to carry ready for launching. That 600 watts figure is more a depth gauge however and won't show detail. The 1500 watts will show rocks and smooth, differentiate between weeds and fish, and begin to let you know bottom hardness. A 2000 watts unit penetrates weeds far better.

Some brands with good reputation for reliability are Lowrance, Humminbird, Eagle, Northstar, Interphase. Their complexity, power and cost vary.  Eagle are like a Lowrance without the unit-to-unit information sharing features. Eagle have a lower power rating than their comparable Lowrance version.  You will get longer out of a battery on Eagle, than a Lowrance, but the Lowrance with it's greater power will show tinier details on screen if that is what you want. Humminbird used to be less reliable than Eagle or Lowrance but in recent years and newer units HB seem to have beaten that problem.  For size guidelines: a screen with a diagonal measurement of 3 1/2" to 5" seems right on a tube. Humminbird and Lowrance are the side looking makes, if you want that feature. Lowrance Eagle and Northstar are the best and clearest downlooking display at the moment, which is the fundamental feature.

Cheap units are just that, cheap! They will disappoint you with their performance. Don't fall for the marketing propaganda that says "costs half as much - just as good as xxxx". The Smartcast is an example of a sonar that just about works, but does not have good enough quality to tell you anything about the bottom, just that it is there. A simple weighted plumb line is more effective than these (it allows you to feel the bottom hardness) and costs nothing. The Smartcast is a useful bottom depth device if you don't plumb, and I notice that shore based bank anglers like them. But by now you will realise that serious anglers, afloat on the water, expect much more information than just the depth from a sonar unit. So recognise that there is a quality threshold in these items, and don't "cut-price-yourself" into getting something unsuitable.

Quick Guide to Choosing the Right Float Tube Sonar

Power of Unit:
If all you want is to see the bottom and know the depth 600watts to 800watts will do fine.
If you want to see the bottom and fish in mid-water, but weeds and fish will get confused sometimes, get an 800 watt to 1000 watt sonar unit.
If you want to see the bottom, what sort of bottom (hardness), fish mid-water, fish near the bottom, and most of the time tell the difference between weeds and fish 1500 watts and up does this. A 1500 watt unit has sufficient power for all float tubing depths.

Screen Size:
A 3" screen only shows minimal information.
A 4" screen shows medium detail
A 5" screen gives you all you will ever need from a tube
The cost of units is more related to the screen size than the power, but that figures in the cost too.

Battery Size:
A sonar that uses AA or AAA size batteries is too weak and toylike for meaningful service. Look at the battery page for portable power source suggestions.

Look at exactly what you need, be honest with yourself in acknowledging what you need it to do, and save up for the lowest that does it properly. That way you won't have to trade up and buy twice.

Most anglers look at their sonar fishfinder and all they see is the depth.
But it tells much more if you can understand the way little things are displayed by these units.
So it's a good idea to learn how to interpret what appears on screen.

Here are three excellent tutorials for you to read:

Lowrance Sonar Online Tutorial

Deciphering Sonar Charts by Luke Morris

Understanding, Using and Interpreting Depth Finders

Is colour worth a bit extra?
Does colour give you advantages over black and white while fishing? The answer is - it depends on how you fish.
The more you fish for species that swim in mid-water, like roach, surface feeding trout, rudd ... the less colour is necessary. Any big return in mid-water is a fish.
The more you fish for fish that live on the bottom, like bigger trout, bream, pike, perch ... the more difficult it becomes to tell what is bottom and weed, and fish. They get mixed up. Lots of practise is needed to figure out a black and white bottom sonar chart, but you can figure it out (with a good unit) because they are different shades of grey.  A colour chart plots softer items in one colour (weeds) more solid items in another colour (fish) and the rocky bottom in another different colour. You don't have shades of grey, you have different colours helping your eyes to separate images apart from each other and recognise them.
Black and white monochromatic screens do have two unique advantages over colour.
They cost less. They are easier to see when intense sunlight is shining directly on the screen (in this situation) colour screens seem to go a bit "gray" and the colour appears to fade.
Let your mode of use, and your budget decide.
Beam Width
If you are planning to tube in under 15' of water then due to the relative shallowness of the water your sonar footprint will be small, unless you get a wide angle transducer. The shallower, the less you will see.
It is a cone shape, so the shallower you are floating in, the smaller the cone, the deeper you go the larger the cone.

For example:
In 10 feet with a 20 degree transducer your sonar beam "illuminates" a circle of 3 1/2 feet diameter.
In 15 feet, you are scanning a circle of 5 1/2' diameter.
In 20 feet, you are scanning a circle of 7' diameter.

Say a 5' circle under you is disturbed by your presence, but you are looking at an outer circle of lake bottom which goes 1' farther each side of that 5' circle below.
The wider beam also takes in more "stuff" which increases clutter. Note that the wider beam spots a structure feature at a greater distance ahead while you are moving.

Seeing fine detail of fish, separate fish, separate weeds, and structure with clarity is easier with a narrower angle xducer.
The narrower beam spots new items at a nearer distance to under you while moving.

How wide is enough? It varies according to your taste.
From my tube. My preference is about 20 degrees.  Shallow water anglers should maybe think in terms of 40 degrees.

While tubing, much useful information is coming from the sonar and a fishing map. Your eyes and the fish (nibbles, takes) supply the rest of the information that goes into making good decisions. But if you never take your eyes off the sonar display you will miss out on a lot.

Here are some handy "estimates" of the coverage footprint of the commonly available sonar cone angles for the depths we mostly fish in:

Beam Angle  :  Cone diameter

10 degrees = 1/6 x the depth
20 degrees = 1/3 x the depth
30 degrees = 1/2 x the depth
45 degrees = 3/4 x the depth
60 degrees = same as the depth
90 degrees = 2 x the depth


GPS-Sonar Combo units
It can be near impossible to locate a spot 3 metres wide when you're 600 metres out from the shore on a featureless surface of water. The GPS sonar combo units solve these difficulties and bring some amazing fishing techniques to your fishing toolbox. Marine GPS units are different from handhelds, they have more compatibility with computers and other units to exchange information. A handheld GPS - while it gives location - might not have all the features you need, unless it can "talk" with the sonar. These are covered under "Making fishing maps"
Sidefinders & sidescans vs conventional sonar
A "side finding" sonar can help locate fish holding off the bottom near a shoreline. This is useful if you are casting towards the shoreline from a position out in the lake. This would be a major help for fishing for rudd in particular. They are also good for spotting trout patrolling along the shallows looking for a meal. their bottom display is of lower quality than other types.

The Humminbird-Bottomline Fishing Buddy will provide this sort of information.  You can be finning along, "see" a couple of fish 30 or 40 feet to the side of the tube, turn and cast a fly out the approximate distance, and get a quick take resulting in a hooked trout. With no sidefinder, unless they make a rise (were you looking at the water or the sonar?) would you know the fish was there? The Fishing Buddy units are liable to also show other "stuff" that is not fish at the same time, especially when looking into the shallows. So a little study at interpretation helps.

For a flyfisher in shallow water, vertical view and seeing fish beneath the tube isn't so useful apart from knowing the depth and water temperature. Flyfishing with floating line is lateral not vertical so the features of side looking sonar units are attractive to fly fishing float tubers.   You will naturally have a greater interest in side view sonars when you cast and retrieve whether it's spinners, plastics, or flies that you tie on the line.
This make the side scan structure view from Lowrance HDS and Humminbird side imaging units more interesting to consider, but heed this expense warning - side view works best on a big screen, and large screen units cost a bundle!

Remember your own style of fishing when reading up on the sonar units and coming to a decision. The extra features are nice but the essentials are dictated by your own mode of use.

The transducer mount
Your transducer (xducer) must be facing downwards, and held steady if the sonar is to show the bottom correctly.
Try to get the handiest type of transducer when purchasing your sonar unit. There are xducers designed to be glued inside a boat hull, sending their signal through the hull, they look shoe-shape rather like a mini travel clothes iron. Others types are designed to stick on the outside of a boat like a limpet mine. They are vulnerable to being knocked by rocks and damaged.
A third type of xducer is designed to bolt onto the transom (rear) of a boat in front of the outboard motor - and this is the handiest type to get for a float tube. The L-shaped transom mounting bracket included is ideal for bolting onto a home made float tube mount. 

The Lowrance "Skimmer" transducer is of this type and is very handy for mounting sonar on a tube. It comes with mounting brackets that allow you to secure it to an aluminium strip or tube, wood dowel, PVC, golf club handle or old landing net handle or a section of broken fishing rod. Next position it so as to have the sonar beam pointing vertically down.  Bungee cord is great for doing this, low cost and easily available. Take a look at the xducer (right) on my float tube. Once the tube is afloat I simply push it into a vertical position ready for use.

Batteries & Chargers - Powering it up
Normally we are looking for a source of 12 volts onboard our tube. The standard answer is a sealed lead acid (SLA) 7 amp 12 volt battery. It has plenty of juice to run a sonar continuously, without worrying about running the battery down.

here is an improved version called Gel Cell batteries. these look the same as the lead acid, but the chemicals inside are in a gel form and cannot spill and ruin your equipment.
These batteries like to be recharged as soon as possible after use. So don't leave them for long in a discharged (empty) state, because it shortens their life substantially. Recharge with the correct trickle charger as soon as you return home. A trickle charge for this size of battery is 700mAh (3/4 amps), and takes 10 hours from empty.

Hobby shops and camping shops sell them.

There is an alternative option to the SLA. This is the smaller, more compact, lighter and faster charging modellers RC battery. Not the kind you get in an electric car with 6 or 7 individual cells in the pack. You need to get a 10 cell pack which will have the desired 12 volt rating. Easier to carry, can be recharged in 1/2 hour, smaller to fit in your tube pockets. What is the catch? It will cost you more than the standard SLA.

For a full description of the use of batteries in float tubes go here: Power Afloat - Float Tube Batteries, and Battery Alternatives