Good idea. Here's another item that I'm sure you've already considered. With the multi bolt hubs compression and clamping force really may not be that much of a problem. The single bolt hubs have more of a clamping force problem if they don't have an additional anti rotation pin in the hub.

I've been thinking that the dis-similar metals between the prop hubs and the prop bolts may be what's causing things to loosen up. I don't believe that a correctly torqued prop bolt is compressing the wood more as it's used, but the difference between steel and aluminum may be playing a big part. Perhaps stainless steel screws may be better suited to the task with aluminum hubs.

I didn't know you made bows, Pe. Now that's craftsmanship!!