Caution: the use of water knifes requires extensive testing. You may need top customize the knifes so they work well with your boat. Water knifes that are not properly shaped and positioned can hinder turning.
These are water knifes (turn fins) for RC Boat, which are supposed to control the turn and make the turn more manageable.
They come with a mount, and the knife angle is not adjustable.
100% fill definitely recommended.
When there are existing screw holes available at the back of the hull, by all means use them to secure the water knifes. If not, using a combination of super glue, A/B glue and hot glue may still do the job (of course not as secure as being tightened with screws).
Water knife for RC Boat (smaller, for boat < 45cm long): upgradeparts-rcboat-waterknife-small
Water knife for RC Boat (smaller and shorter, for boat < 45cm long): upgradeparts-rcboat-waterknife-small-shorter
Water knife for RC Boat (larger, for boat > 45cm long): upgradeparts-rcboat-waterknife-big
Water knife for RC Boat (larger but shorter, for boat > 45cm long): upgradeparts-rcboat-waterknife-big-shorter
This is a very small one for shallow water: