The boat that inspired me to start this thread has a live bait tank with a glass window built into the transom, which is nice, and has some advantages, namely being able to reach the fish to use them. When your live bait tank is in the hull of the boat way down low, and the water level is quite far below the deck level, it's hard work extracting fish from the tank. On the other hand, if the tank is up high, it is riskier and more difficult trying to put fish INTO the tank, which is sometimes a high speed task (bonito handlining for eg). Another aspect of having the tank up high is that a pump is required to keep the water circulating. With a hull tank and smart use of scoops, it's self feeding, even at anchor. Some further points:
- The above-deck bait tank in that boat had a recessed toe area below it, nice idea!
- Square cornered tanks, square tanks in general promote fish damage as they crash into the walls
- If using scoops to feed the tank, angling them at about 45 degrees allows the swing of the boat to circulate water
- If using scoops, while going fast the supply of water can exceed drainage out and increase the level
- If drainage out is from the rear (the obvious choice) most of it should be near the high tide mark so that if drainage exceeds supply, level doesn't fall
- A single drain RIGHT on the floor of the tank is very useful to fully evacuate it at speed after blocking the feeds
- The bottom of the tank must be made of thick abrasion resistant material (eg an inch thick of solid fibreglass)
Having both an above-deck and below-deck/in-hull tank would be great. You could literally have the best of both worlds. The below tank would be self-maintaining and the above tank would be only used when required/desired. If unused, it could be used for storage instead. The space it would take up would not be very useful anyway. If having an above deck tank, it would make sense to place it centrally.