Kingfisher111's Live Bait Tank Edit
The purpose of this project was to design and build a live bait tank for my Hobie Outfitter Fish (tandem) Kayak as cheaply as possible. This would involve using as much material from around the house as possible, minimising the need to purchase specialty parts.
Originally I had considered using just a simple aerator in a bucket as a live bait tank, but that would not keep the bait in the required condition over several hours of fishing. In order to keep live bait as lively as possible over several hours, there are three things which are necessary:
1. Keeping the water aerated,
2. Keeping the water temperature relatively constant, and
3. Preventing a toxic build-up of ammonia and nitrate.
The first can be achieved simply with the use of a bucket and aerator; however, this setup will not achieve the last two points. The second and particularly the third are best achieved by regularly replacing the live bait tank water with fresh water. With this information in mind, and after researching live bait tank design for larger fishing vessels, I decided on building a tank that would circulate the tank water while replacing old water with fresh water from the ocean, lake or river. The only practical way to do this in a kayak is with the aid of a water pump.
Finding a suitable container
The first decision you will need to make is what is the appropriate size for your live bait tank? In relation to preserving the quality of the live bait, the bigger the better, but the tank must be small enough to be practical onboard a kayak. I have seen other kayakers using 9 litre buckets or 10 litre boxes, but in my opinion the minimum size for a bait tank should be 20 litres unless there is no possible way a tank of that size will fit on your yak. Look for containers with substantial height as this will allow you to minimise the footprint of the tank while maximising its volume.
I took the measurements of the area on my yak where the new tank was to sit and began to look around the house to see if I could find a suitable container. I ended up liberating a 30 litre clear plastic box that was comfortably within the size limits of my yak. You can opt for a coloured container if that is all that is available however I recommend clear as it enables you to quickly check the condition of the live bait at a glance. If you must choose a coloured container, try to go with light colours, as darker colours will tend to absorb sunlight and consequently heat the tank water (white 20 litre drums are popular choices for live bait tanks).
Choosing a suitable water pump
Now that the container has been selected, a pump must be sourced. Purpose designed bait tank pumps are available from tackle stores at a cost of around $70 and come with all the fittings required to give the project that professional look. As I was not prepared to pay $70 for the purpose built pump, I bought a $17 Johnson bilge pump from my local boat store.
When looking for a bilge pump to use for a bait tank, go for the cheapest model available with the lowest flow capacity. The reason I say this is that the $17 model I bought had the lowest flow available for a bilge pump that I had seen and it is more than enough. The cheap bilge pumps will pump 350-400 gallons per hour which works out at approx 30 litres per minute. Working with a 30 litre bait tank, that means the tank water is completely replaced every 60 seconds, which is far from being too slow - in fact, I recommend slowing the rate of flow further (see the section on wiring below).
Miscellaneous hardware required
Now that you have your container and your pump chosen, you will need to connect the two of them together. I used clear tubing as it was the cheapest available in the boat shop where I bought the bilge pump ($2.50 per meter). You can also select some custom elbow connections (as I did) which, although not required, add to the functionality of the tank.
The bilge pump must be submersed in water to work and is best attached to a hose and hung overboard. It is a matter of preference but I fashioned a spray bar to diffuse the incoming water flow into the tank and assist in water aeration. To make a spray bar simply drill several holes down a piece of tubing cut to the length of your tank height and plug the end.
Now that you have your water intake installed, you will need to consider where you want your waterline (consider leaving room for movement onboard your kayak). One important thing to remember is to put the tank’s water inlet (ie. the outlet from the hose connected to the pump) above your desired waterline. If the inlet is below the waterline, you will unintentionally begin to siphon water out of the tank when you turn the pump off.
Now that your waterline is decided, you will need to create an overflow outlet to allow the water above your desired waterline to escape. Although a simple hole (or series of holes) is sufficient, I attached a hose and an elbow to allow me to direct the overflow towards the scuppers.
Another consideration is how you plan on accessing your live bait. As I often use poddy mullet (which have a propensity to jump out of tanks), I needed to be able to grab a bait without giving the other baits a chance to escape. In other words, I needed access to the tank without removing the entire lid. In order to do this, I cut a hole in the tank lid and inserted a cheap Tupperware container with its bottom cut out.
The bilge pump is designed to work from a 12 volt marine battery, and if you have one in your yak already to power your sounder then you may wish to simply wire the bilge pump straight to it. I run a 7ah 12v battery on my yak, and my sounder can easily drain 5ah during a normal fishing session so I like to use a separate power supply for the pump (my sounder is a power hog – rated at 4000 watts peak to peak). A bilge pump will draw around 2ah so you will need to consider whether your battery can supply your sounder and the pump or whether you need an additional power supply.
If you are looking at a separate power supply, I recommend a 6v battery (as opposed to 12v) as this will slow the rate of flow of the pump to a more acceptable level.
Keeping with the project objective of keeping costs low, I located 2 old battery packs from a radio control car. They are 7.2v packs rated at 1400mah (but due to their age are only now storing 1000mah and 600mah respectively). Together they will give me less than 2ah which is just under 1 hour of pump operation. Although this sounds insufficient, I have never had to resort to the second battery in testing. The reason for this is that the pump does not need to be left on constantly. Recalling the fact that the pump is capable of replacing the entire 30 litres of tank water in one minute, the pump only needs to be run for a minute or two every 15-20 minutes in order to keep the fish healthy.
Basic wiring option
Wiring the bilge pump is extremely simple – attach the wires to a battery and the pump starts pumping. I had a basic on/off switch lying around in my toolbox so I connected the battery to it and installed it in a spare Tupperware container that I found in the kitchen (provides a waterproof housing for the batteries). The switch enables me to simply flick the unit on every 20 minutes or so and flick it off after 2 minutes.
Advanced wiring option
This advanced wiring option is not required for basic operation; however, as I had the electronic components already in my toolbox I thought I would add a handy delay timer to the switch (the cost to build this delay would be around $15 with parts sourced from Tandy/Radio Shack or Dick Smith).
With the basic wiring above, the user is required to switch on the pump and then remember to switch off the pump after the pump has replaced enough tank water. The advanced wiring option allows the user to simply press a button and the pump will automatically switch on and then switch itself off after a user-definable delay period (the delay can be adjusted with the turn of a knob).
The parts required for the advanced wiring option are:
1. 1 x miniature relay with 9v coil and single changeover contacts
2. 1 x PNP (positive negative positive) transistor - 558
3. 2 x silicon diodes – 1N914
4. 1 x power diode – 1N4002 or 1N4004
5. 1 x integrated circuit timer – 555
6. 2 x capacitor polyester (green cap) - .01uF
7. 2 x capacitor 6.3v tantalum electrolytics (orange cap) - 47uF
8. 1 x resistor - 10k ohms (brown, black, orange bands)
9. 1 x resistor – 6.8k ohms (blue, grey, red bands)
10. 1 x resistor - 47k ohms (yellow, violet, orange bands)
11. 1 x variable resistor (potentiometer) – 1m ohms
12. 1 x momentary action push button switch
13. 1 x single pole/single throw switch
Other pre-packaged, ready to solder timer delay kits are available from model train stores and electronic stores such as www.hobbyengineering.com
Prior to testing in the field, I recommend testing the unit at home with the use of a bucket. Here you can see the spray bar operating as intended.
Using the live bait tank during a fishing session on a warm summer’s day (around 25 degrees), I was able to keep poddy mullet alive (and healthy enough to release at the end of the session) after seven hours of captivity. I switched the pump on once every 15-20 minutes for around 2-4 minutes, and I was not required to connect my spare backup battery pack.