You can enable custom depth rendering to render boad to a custom depth\stencil buffer. Enable it for your boat and set stencil value to 1 for example. In water material you have to set water alpha to 0 on any pixel which has stencil == 1
You can enable custom depth rendering to render boad to a custom depth\stencil buffer. Enable it for your boat and set stencil value to 1 for example. In water material you have to set water alpha to 0 on any pixel which has stencil == 1