Bulb shape is at least as vital as everything else under the water. Various trick shapes have been tried, but the winners all gravitate to an elongated teardrop/torpedo shape. To maximise the righting moment, the CoG of the weight needs to be as low as possible so some have tried a flat bottomed triangular cross-section, but at the same time drag has to be minimised, so the circular section prevails. Full size yachts have a crew, who do their level best to ensure that their boat stays as upright as possible, so strangely shaped ballast weights that benefit a boat sitting vertically in the water work for them. Most model yachts don't, either because of class rules or because the gains are outweighed by the losses,.