>>Got to ask, what type of plywood did you use and how did you store it?
It was a regular (not waterproof) plywood, coated with 2 layers of epoxy. The boat was stored inside, hanging with the bow pointed down (that's how moisture was getting in)

>> If one rotted away that quick there has to be a reason.
My theory is that the bow is always working, especially in the waves. This, in time, creates tiny cracks between layers of plywood. Once the cracks developed, the rot followed quickly. I suspect that a solid wood coated in epoxy might last longer.

>>I have a couple much older than yours and in fine shape.
How often are they used? Mine was a few times per week, for about a year. Also, you may think the plywood is OK. I thought so as well, until the bow almost fell apart. The rot must have existed long before, but it was not so noticeable. There is no way of knowing how the wood is doing all the way up in the bow until you cut the fabric open.