Improvised fluvial drifting mine - the fishnet orange float is used for floatation and masking the device as a regular fishing device - the attached mortar bomb detonates the device when encounteering the hull of a boat - the riverine patrol boats had a fiberglass hull, and the LCMs hull was not much stronger.
The vietcong in 1968 used quite a variery of mprovised device for teh mining of the Cua Viet river. A report speaks of "C-rations, boxes, tree limbs, plastic spheres and fish floats, a bright blue swim fin and otehr flotsam or jetsam of no partculiar distinction - all might conceal or buoy a drifting mine. Recovered devices include some that were manufactured in part from scrap Styrofoam, cloth, string, wicker baskets and inner tubes...."