Use a scribe and a sheetrock knife to carve a piece of cardboard so it fits the curve. Then carve another piece of cardboard that fits into the curve of the first. Now you can use that to carve and scribe into a chunk of wood too big in all dimensions. Once you have the inside curve right power plane what remains into curvy triangle that fits onto the front of the boat. You might make that stem blank by laminating several bits of one by.
Cardboard is a pattern makers good friend.